Page 7.58 (11,104)
Return to WhittSflying
Return to IFR Contents
In the Beginning; ILS Charts in the Making; IFR Approach Basics; Prevention Plan for ILS Mistakes; Need to Know ILS Things; Use All Your Navaids; At the Marker; ILS Specifics; About the ILS; Flying the ILS; Downwind ILS Approach; Personal IFR Limits; DME; DME Arc; Bracketing; Centered Method:; 10 Degree Method:; ...DME ITEMS;... DME Arc Another Way; ...DME Requires a Different Kind of Anticipation; ...ILS Approach; ILS Method; ILS Another Way; Single Pilot ILS; ...Taking Charge; ...Pre-Approach ILS Set-up Order of Importance; ...Eight Stages of the ILS; Fly the ILS with Rudder; ILS Partial Panel; ...Partial Panel Is an Emergency; ...Instructional Exercise; A Better ILS; ...ILS Dot Measure; ...ILS Accidents; ...ILS Safe Space; Downwind ILS;...Category I ILS; ILS Failure; Catching ILS Malfunctions; Emergency; ILS and TERPs; PTS for ILS; ILS Test:; ...ILS-IFR-PTS; Rule of Thumb Compass Turns; ...ILS Glide Slope; The Glidepath Is Not a Glide Slope...The ILS from 200 Feet; ILS Basics; ...ILS Winds ILS Back Course; Timing the ILS; ...Hands-off ILS; .. ILS Parameters; ...False Glide Slopes; ...Monterey Plate; ...
For many years the search was on for a zero-zero system. This has only in the recent past become possible. Once a 200-foot minimum was accepted as the best available things began to improve.
In 1918 the first marker beacon was demonstrated. In the early twenties the first four-course radio range was demonstrated. This could get you from point to point but not on the ground.
In 1928 the concept of an ILS with the heavy equipment on the ground and the indicators in the airplane was accepted. A cooperative effort by the Guggenheim Foundation used Jimmy Doolittle to contact the Sperry Gyroscope Company to get them to develop two needed instruments. Sperry created an artificial horizon (Now called an attitude indicator) and a gyrocompass (Now called a heading indicator) which gives precise and easily determined information. Doolittle used a localizer beam to guide him to the airport and a fan-marker as a means for determining distance from touchdown. The last remaining necessary instrument came from the Kollsman Instrument Company. In August of 1929 Kollsman perfected a barometric adjustable altimeter that gave vertical information within 20 feet. At the end of September Doolittle flew a localizer approach to touchdown
At the same time a high frequency glide slope beam was being developed at College Park, Maryland which by 1931 was blended into a three element landing system consisting of a localizer, marker beacons and glide slope. Marshal S. Boggs made a blind landing on a runway whereas Doolittle had landed on a large field. Boggs' localizer was accurate to 20' at the threshold. The glide slope was accurate to five feet when 30' above the ground. Boggs made over 100 such landings but always with a safety pilot. Jim Kinney took over for Boggs who was killed while on vacation. Kinney completed the first IFR flight from takeoff to landing by flying in clouds from College Park to Newark. Lindbergh made two ILS approaches using a safety pilot. The project was killed in 1933 by the withdrawal of federal funds due to the depression.
When the federal government dropped the ball the airlines were interested but an ILS system cost over sixteen thousand dollars and $600 more to equip an airplane. Then when the expensive airmail contracts were canceled, the U.S. Army began flying the mail. In five months there were 66 accidents. Then the government became interested in a landing system, not the ILS, but an NDB system with markers. Using this system Lt. Al Hegenberger made the first solo blind landing ever at McCook Field Ohio. Because of Hegenberger this system became the government's favored system and it was so primitive that it could be federally financed because it was not an airport improvement. The airlines were unhappy, knowing that the ILS was waiting in the wings.
TWA developed and tested a high frequency ILS system in Germany but again it was not precise enough for the airlines. In 1935 some scientists who had left the previous government ILS started their own company and developed a portable ILS that could be moved from runway to runway. This system was supported by and adopted by the Navy for land use.
In 1934, United Airlines acquired the original Newark ILS
equipment and moved it to Oakland, CA. This was installed as
a permanent ILS as modified in 1936. In March of 1936 R.T. Freng
in a Boeing 247 flew an autopilot coupled ILS approach. Over
3000 such approaches were flown over the next two years. Other
airlines, and the military services were involved.
When five airline crashes occurred in December the government initiated a well financed airport modernization program. In 1938 the first passenger-carrying airline landed at Pittsburg, PA using the ILS in actual conditions. The first United-Bendix ILS systems were installed at Burbank, Oakland, Kansas city, Chicago, Cleveland and Newark. In June of 1938 the 1926 restriction was erased from the books. However, before WWII began only one government installed ILS existed. During the war eight civil airports and 29 army fields got ILS installed. During the war the military favored the Ground Controlled Approach system which was radar controlled from the ground. This system is expensive and manpower intensive. The ILS finally won out but only as a low approach landing system. I have read of one instance where the portable version of the ILS saved a C-46 on one engine in a Himalayas airport of northern India during WWII.
Charts in the Making
Charts are made following the rules of FAR 97 which requires that a text presentation of the chart be made as a proposal or a proposed rule making based upon the U.S. Standard for Terminal Instrument Procedures or TERPS. +Safe flight is the primary basis of chart design.
1. Obstacle clearance slope is folded in with the need for a smooth descent.
2. TERPs standards are followed as much as possible.
3. Non-TERPs standards must be fully documented.
4. User and other agencies have time to make comments.
1. Initial approach made of DME arc, radial, course, heading vector or a combination as the initial approach fix (IAF) as a beginning point. This segment has 1000 feet of altitude above an obstacle and narrows from 4 nm to each side of center at 13.5 miles from the threshold down to1/2 m at the inner marker. A secondary area gives 500' obstacle clearance beginning at the 4-mile primary area to 6 nm and narrows to the same 1/2 mile at the inner marker as the primary area.
2. Intermediate approach begins at the end of the initial approach segments where you configure the aircraft and adjust the speed while setting up on the positive approach course.
3. Final approach begins at the FAF and ends at the runway of missed approach point.
4. (Optional) The circling approach has a region adjusted to the speed of the aircraft. The maneuvering area allows the aircraft to remain with the airport in view while it flies to arrive in alignment with the runway before initiation of the descent.
5. The missed approach is a point from which the aircraft rejects landing as a possibility and climbs to depart the procedure.
Flying the ILS requires the pilot to process four times the information a surgeon doing a major operation. Outcome is result of three basic factors:
1. Pilots knowledge of aircraft
2. Pilots ability to fly smoothly and competently
This is region of greatest weakness. Pilot must have feel for what the airplane is doing. You must learn to slow the aircraft to approach speed at a time and place commensurate with your altitude and the required airspeed configuration.
3. Situational awareness.
You must know exactly where you are in relation to the airport and final approach fix. When you are in strange territory and have unfamiliar approaches and departures, the wisest thing to do is to ask for help from the locals. You can expect that every departure will be somewhat different due to local procedures that often bypass those published. Expect to get an amended departure in the run-up area that differs from everything you have planned. Expect that with the advent of GPS that even your enroute plans will be augmented by GPS-direct to an intersection that bypasses a busy corridor.
The criteria of IFR proficiency is based upon your ability to adapt to the unexpected. An instrument departure is given in your clearance as a road map. Before flying any part of the departure, en route, arrival, or approach you MUST review not only what you expect but what you may get. Major problems can result if any part is totally different from what you planned. As to what causes these differences it may be due to weather, aircraft performance, human limitations, or even ATC restrictions. Getting or requesting radar vectors is often a valid option.
In the planning of IFR flight you must pick off as much in the way of names, courses, distances, frequencies, and change-over points, and minimum altitudes from the plates and charts as seem to follow your route. Expect ATC to be as helpful as they can be in giving you requested altitudes, deviations, or special considerations. Let them know if you have a problem and keep them advised of any significant changes. You want to know your chart information so well that any search only takes the recommended three seconds off your flying scan.
In the flying of IFR scan is your first priority. If a clearance
disturbs your scan tell ATC to give you a heading long enough
for you to get the rest of the clearance. Single pilot IFR is
ten times more difficult than two pilot IFR. Even with autopilot,
single pilot IFR requires more practice and proficiency that
is required when two pilots divide the work load.
The student who chases the localizer and glideslope needles by jockeying the power and elevator is going to be in ILS trouble when the funnel narrows.
--Cover up the AI.
--Have student concentrate on the DG, VSI, and airspeed.
--Set power to get the desired approach speed and descent rate.
--Crosswind components usually decrease with altitude.
Prevention Plan for ILS Mistakes
Just as an accident is preceded by a series of judgment mistakes, so is a defective ILS approach preceded by a series of planning errors. Well away from the airport get the ATIS; Check the FSS for recent NOTAMS. Review the plates. Confirm the basics of the Missed. Listen to what is happening to aircraft ahead of you. Check to make sure that you get what you expect in descent and headings. Set up your GPS as a situational awareness guide. Expect to execute the missed. Review your pitch and power setting for every stage of the approach. Remember: Wind will never be what they say it is.
to Know ILS Things:
1. Know the dimensions of the localizer course.
2. Intercept and descend on localizer before reaching the marker.
3. Set power and trim for stabilized approach airspeed.
4. Keep track of where you are and what to expect.
5. Have the needed numbers before you need them.
--Set the radios
--What you hear...not what you expect
--Familiarity with region
--Know point to point distances and times
--Organized copy sequence
All Your Navaids
1. ADF needle on frequency and pointed to marker.
2. Set and verify frequencies
3. Check for flags
4. Move with the marker to find primary heading.
5. Write and use your pitch and power transition settings.
1. Be prepared before you get there.
2. Write, know and set the numbers. Verify.
3. Inside the marker you just listen to ATC.
4. Maintain orientation and situational awareness
Middle marker (amber)
A point on the ILS glide slope Final altimeter check. MM should be part of briefing. The middle marker is 1/2 (3500 feet) mile from runway at decision height which is typically 200' AGL above TDZ. MM inoperative does not change minimums as of 1993. Check the marker crossing altitude as an altimeter check. The middle marker is not a required component for full ILS minimums nor the localizer
1. One mile out one degree is 100' or one dot. 200' equals 200'.
2. ATP standards are one dot deflection calls for a missed approach.
3. If you have not stabilized your descent you will lose the localizer as well.
4. Pitch to an airspeed and power for descent rate.
5. Inside the marker pitch to glide slope and rudder for localizer.
6. Know the pitch-airspeed-trim setting for the glide slope.
7. Localizer sensitivity is 2.5 degrees from center to side.
8. If localizer needle waves, change propeller rpm.
The ILS has two fixed beams , the localizer provides left/right orientation and the glide slope provides vertical slope. However there are several glide slopes, only one of which is correct and verified at the final approach fix by the altimeter check. The false glide slopes provide a very steep approach which may be difficult for slick aircraft to follow. By the time you recognize the problem the missed is the only option. By keeping the localizer and glide slope indicators centered you will be flown right to the end of the runway. This can be done by the pilot or by the flight director. The ILS problem is that only one aircraft can use the ILS at a time or about 20 per hour.
Cat 1 ILS at DH requires:
1. See runway environment
2. Continuously able to make normal descent to landing
3. Required flight visibility.
Until the GPS WAAS system is perfected, nothing gets you closer to the runway than the ILS. The lateral and vertical guidance will fly you into a blackboard-sized space called the decision height or (DH). The DH is the missed approach point. You either see the runway or you go missed.
The components of the ILS are a localizer, markers and glide slope. The localizer is an antenna that sends a beam along the runway centerline out some 18 miles and up to 4500 feet. It also sends a signal out backwards called the back course. Depending on your equipment you will always fly to the needle to center it. The difficulty of a back course is that you will not have a glide slope and may need to fly away from the needle to keep it centered. This reverse sensing is also true if flying outbound on the localizer. The localizer's full deflection is 350' to each side of the center line at the runway threshold this full deflection is only 2.5 degrees wide to each side. The OBS has no effect as it does with a VOR. The pilot is well advised to set the OBS to the runway direction the approach. On the missed immediately set the OBS to the VOR intercept that is usually a part of the missed. Be ready to change the frequency. Having a heading bug to set in the course or possibly the wind direction will give an added assist.
The glide slope is offset from the runway and sends a signal that is fifty-feet above the runway initially and slopes up on the true glide path to 1400' AGL near the outer marker. At ten miles out a full-deflected glide slope is 1500 feet off the center. At the threshold the full deflection will be close to five-feet. At the middle marker it is 200'. The glide slope is 1.4 degrees to full- high or full-low deflection.
Marker beacons are disappearing to be replaced by radar or intersection fixes. The middle marker is no longer required. Still remaining are the false glide slopes waiting for aircraft to be vectored into harms way. Only the outer marker remains to show the pilot the point on which to measure his altimeter setting accuracy.
Part 4 the Middle marker (amber)
A point on the ILS glide slope Final altimeter check. MM should be part of briefing. The middle marker is 1/2 (3500 feet) mile from runway at decision height which is typically 200' AGL above TDZ. MM inoperative does not change minimums as of 1993. Check the marker crossing altitude as an altimeter check.
A localizer has a four-letter code beginning with I to verify the localizer frequency. Failure to identify the code is a checkride bust waiting to happen. The Category I ILS has 200 -foot minimums while requiring 1/2 mile visibility. Larger airports with RVR reading and runway lights have different visibility minimums.
Flying the ILS requires gentleness and accuracy of control movement. One technique I advocate is the use of yoke for altitude and decent control and rudder for heading changes. Airspeed is set with power. Airspeed can be set best by the use of pre-determined power settings.
The basic skill required of all instrument approaches is that of fly headings and altitudes. If this basic skill has a deficiency then the pilot will be overwhelmed by the additional details required of by the approach. Because of the funnel like increase in required flying precision of the ILS, the pilot must sense the changing sensitivity control requirements as the approach proceeds. The winds of change are a part of flying the ILS. My particular hometown LDA approach has more unusual wind directions and velocities than anyone would normally expect. Just two days ago I has occasion to have a student track the localizer with 90-degree 40-knot winds directly from the right up until we reached the outer marker. The wind changed from the right at only 20 knots inside the marker and at the runway gusts were 20 knots right down the runway. Keeping the needle even close was a composite of luck and skill.
Speaking of winds, a tailwind, decreasing headwind, light and variable wind, or no wind at some point on the approach will play havoc with your ability to time the approach, providing you remembers to start the timer. The vertical speed required to fly the approach is based upon ground speed. Your ground speed can be/will be just as variable as the wind. Accuracy is a crapshoot. Use the projected rate of descent given on the ILS chart for the ground speed you hope to maintain. A DME is a BIG help in adjusting your ground speed. My suggestion is that for a localizer type approach you select a vertical descent that will get you to the MDA about one minute before the projected time to the MDA runs out. MDA's time runs out at the runway threshold and makes the required normal landing unlikely. By moving it up a minute on the approach it at least gives you a shot at normalcy. The vanishing Visual Descent Point used to do this.
A major instructional problem is accomplishing desirable instructional ends without undue exposure to hazards. IFR actual with turbulence is such a problem. The peril of such a situation is loss of control with a resulting high speed and ultimate destruction of the aircraft. The same conditions could result in loss of control due to low speed. What needs to be taught in IFR turbulence is the maintenance of control because once lost, the control is exceptionally difficult to recover. Successful flight in IFR turbulence is a matter of personal discipline and attention to holding attitude and heading rather than altitude.
It is vital that the instrument student learn the judgmental decisions that make an approach possible. The student must be exposed to the lethal elements of any approach, distraction, below visual minimums and runway requirements. The training program should demonstrate the thought processes required to make both the 'make the approach' decision, and the 'make the missed' decision. A training program that makes every approach successful is not preparing the student for the real world of IFR flying.
I have found that the way you hold the yoke makes a significant difference as to how successfully you will fly through turbulence. A tight grip with abrupt yoke responses to turbulence seems to accentuate the problem. I have found that rudder is the best way to raise a dropped wing and correct heading changes. Yoke is best for maintaining altitude. Don't sweat the altitude changes. Get a block altitude if you can, declare an emergency if you must.
---Hold your headings, ignore distractions and stay ahead
of the approach plate.
---For ILS corrections less is more
---Keep your bank corrections at less than five degrees.
---Use a count system for time of bank correction.
---Use the 12-o'lock needle on the attitude indicator to keep wings level.
---Use horizontal bar of AI to set descent/climb rate
---Trim off all control pressures
---Learn to hold headings and constant altitude changes.
---Eliminate distractions and use mental reserve to flying the approach
---Set up everything for the approach before the marker.
---Approach Checklist Completed is last item on checklist
---Don't try to confirm checklist completed, it's too late.
---Use this system in VFR until you can do it IFR.
ILS PRM (Precision Runway Monitor)
---Parallel runways with simultaneous IFR approach
---NTA (No transgression zone between runways
---Faster, better real-time radar in place.
---Monitoring frequency on plate below tower frequencies, one for each runway.
---All breakout instructions must be hand-flown.
An ILS downwind approach with a DME assist in adjusting the ground speed means that you need not arrive at the DH with excess air/ground speed as would be the case without a means for determining your ground speed. The slope of the ILS is predicated on ground speed and any excess ground speed means you will overfly the slope and have difficulty getting down. A 10-knot ground speed will double your distance over the fence to touchdown and double your ground roll. Any approach or landing of more than ten knots has little chance of success.
With a wet runway your chance of hydroplaning is quite high in a downwind situation. Nine times the square root of your tire pressure is the hydroplaning speed of your aircraft. With a 36 pound tire pressure you have a hydroplaning speed of 6 x 9 =54. Any touchdown speed over 54 means you are sliding as on ice. Not a good option in a downwind landing.
Ceilings of 1500 and 3-5 mile visibility enroute. Emergency airport accessibility. Every engine failure at night has ended in a crash with few survivors. Judgment would suggest that you have a backup vacuum and battery GPS and transceiver. A single engine aircraft requires situational awareness very mile of every trip.
---Where does your skill limit meet the FAR limit?
---Aircraft complexity as a factor
---Will you be able to cope with an unexpected situation or emergency?
---Can you return to your departure airport?
---Think of VFR instead of IFR when down low.
---Donít cross cold fronts down low
---Approaches are always how low to take a look?
---The missed begins when the approach is falling apart
---Know the DH/MDA and put in a VFR factor
---Reject any vector that puts you high and fast to final
---Donít do an final approach that is not VFR
---Night or circling requires VFR minimums
---Legal minimums are not enough.
You cant do the right thing if you dont know what the right thing is.
Dont leave IFR without knowing where nearest VFR lies.
A DME equipment or accuracy check is not required for IFR or any other use but such checks are available at many airports. The installed accuracy requirement is 1/2 mile or 3% of the distance. Such things as terrain reflections or dirty antenna can affect the both operation and accuracy. The DME distance is a slant range and is not as accurate as GPS distance. At 5000 above a VORTAC your DME will read one mile. The closer you are and the higher you are the greater will be the DME actual error. At 13,000 you will never get less than 2-1/2 mile DME reading. The PTS requires tracking the arc within 1 mile of the published distance.
--DME accuracy should be within 3% or 1/2 mile which ever is greater. Code every 37.5 seconds
--DME is slant range so will be different from GPS
--Code is at an unpleasant high pitch.
--DME and transponder frequencies can conflict. Check with transponder on standby.
--Ground speed and time to station are based on rate of change and vary in accuracy.
In the last six months of WWII I was working with a radar nav/bombardment APQ-23 set. This had the first airborne DME which was used to measure the slant range to a target. The bomb release point could be tracked by radar much as a bomb sight tracks visually. The distance read-out was like an odometer. It took 40 years to get the same ability into G.A. planes.
Arc distances vary from 7 to 30 miles. At 100 kts lead turn from radial to arc by 1/2 mile and 90 degrees change (tangent heading). You should know that the obstacle clearance on a DME arc is the same as an airway. Four nautical miles to each side at the specified altitude. Minimum vertical obstacle clearance is 1000' or 2000' if mountainous. For straight final DME segments the obstacle clearance is 2 to five miles wide and 250'. If final is an arc, it is 8 miles and 500'. DME arcs are usually initial segments but can be intermediate, final or missed approach. Since you need to refer to the DME chart often, be sure of your competency to make rapid visual checks of the charts without losing aircraft control. Regardless of the method the lead radial is where you should change over to the ILS frequency. DME arcs are usually NoPT.
DME arc practice can consist of flying semi-circle arcs and varying distances. Flying the arc can become easy by flying tangent headings while comparing the OBS setting and HI. this corrects for wind as well. The radio magnetic indicator (RMI) is a must for flying DME arcs except for the most proficient.
A DME arc procedure flown by your own navigation must begin at a IAF. ATC actually has the option of ignoring the arc and vectoring you into the initial or intermediate segment of the approach. Training can be augmented by departing via an airway to intercept the arc from the inside. Makes student identify and turn correct way. DME arc can only be intercepted at IAF unless otherwise authorized by ATC.
Know the 90 degree heading required when intercepting the arc from a radial. If the DME reading increases, turn into it by 10 degrees. If the DME reading decreases, turn away by 10 degrees. This bracketing method does not provide position guidance and can be difficult in strong winds. It is the low workload method.
--Turn 90 degrees from the interception radial to the arc.
--Turn the OBS to keep the needle constantly centered
--Keep your heading 90 degrees to the OBS radial setting.
--Any changes in DME readings must be corrected as in method #1.
--Turn 90 degrees from the interception radial to the arc.
--Set OBS 5 degrees ahead.
--It is better to initially set 1/2 needle deflection.
--Fly until 1/2 needle deflection to the other side.
--This gives better control over the 10 degrees than with full deflection to one side
--Turn the OBS ahead another 10 degrees.
--Bracket the DME readings as in method #1.
--Only DME distance is required for flying the arc.
--DME is no longer required above 24,000' if you have an IFR certified GPS.
--DME location must be in IFR certified GPS database to be legal in flying the arc..
--Charted arc radii vary from seven to 30 miles.
--Entry from the outside requires that you make an 80 degree heading change just prior to the arc at the IAF.
--Lead the turn to the chordline by dividing one percent of the ground speed by two to get the lead-in distance.
--A 90 knot ground speed would be .9 divided by 2 to give 4.5 nm lead-in required for standard rate turn.
--The DME will count down and then up and then just before you reach the arc, take another 10-degree cut.
--You will remain always slightly inside the arc where corrections are easier to make than when outside.
--Once you are unintentionally outside the arc be aggressive with up to a 30-degree cut for a chord line.
--DME arc airspace is protected four nautical miles up to 500 feet each side of the arc.
--The IFR flight test allows only one nautical mile each side of the arc.
--Should you get two miles inside on your chord line turn 5 or 10 degrees out.
--The 10-degree chord lines only work in no-wind conditions.
--Wind direction and velocity changes will require changes in you chord lines.
--An IFR certified GPS can be used to fly an arc.
--An airspace you wish to avoid can be arced around using a center located VOR or ARP as reference.
--Tune appropriate navaid and OBS for final approach course.
--Intercept turns off the arc should begin ten degrees early.
--VOR needles are alive at the ten-degree point. Localizers twitch at 2.5 degrees so begin early.
--DME arcs can be eliminated by accepting vectors to the final approach course.
--A convex DME arc exists. They can only be entered at an IAF
--DME arcs are well on their way to obsolescence.
---Simplified DME Arc
Use chart to make first intercept turn which may vary in degrees. Identifying lead-in radial is critical and one other along the way. Otherwise, just vary arc to keep distance.
--Technique for 90-degree Turn to Radial
--Lead the turn to the chord line by dividing one percent of the ground speed by two to get the lead-in distance or Ground speed divided by 200 does the same thing but not mentally
--Square the Mach number, ignore the decimal. mile distance to initiate turn
--180kts = 3 mpm or .3 Mach. .3 x .3 = .09 use as 9-tenths of a mile. Round to one-mile for lead-time to turn.
Ė-120kts = 2 mpm or .2 Mach. .2 x .2 =.04 use as 4-tenths of a mile. Round to half mile for lead-time to turn.
DME Requires a
Different Kind of Anticipation
--More DME approaches are requiring a 90-degree intercept to the approach corridor.
--The lead-time for a turn to intercept at approach speed of 90-knots is about Ĺ mile.
--It is better to fly to the inside of the arc since your headings will always be taking you to intercept arc.
--ATC Radar vectors call for a 20-degree angle of intercept if 2-miles from the gate.
--Beyond 2-miles procedures call for a 30-degree intercept. (most common)
--Once cleared for approach pilot is free to fly his own estimate of intercept.
--Occasionally vectors may take you across and back to approach corridor for spacing. You will be advised.
--Approach clearances are given if you are on a published route or an approach segment.
First, set the heading indicator to the compass.
Second, slow up.
Third, get down.
Fourth, set in the missed procedure.
Sensitivity of localizer and glide slope and dual needles make smoothness an essential for success. Fly a heading and a rate of descent. Dont chase ILS needles because you will always tend to over react. If you find yourself doing this, once you have over-reacted immediately take out at least half of the initial reaction. Tendency is to over correct to get needles to stop. The smaller the heading changes on the localizer the more easy it is to keep the needle close to centered. You are dealing with two headings on the localizer. There is one heading that stops the needle and another that brings the needle in. Watch for the heading that stops the needle. Work to the sides of that heading using headings to bring the needle in. When you get close use only the rudder.
Winds change as you descend not only in direction but in velocity. The GPS can be helpful in determining wind correction angle. Always use heading bug to set in the heading you are going to fly. Again, saying the heading aloud is a good way to avoid a too rapid scan. Locking the elbow and arm aloud just prior to reaching for the radio stack is a good way to prevent the inherent turn likely to occur. Limit any time devoted to the changing of radios to three seconds between scanning the flight instruments.
Ideally once you have established the baseline descent between 500 and 600 fpm and the heading required make only minor corrections of power (50-100 rpm) and rudder. to overcome the needle dance concentrate on accurate airspeed, rate of descent and heading. It is helpful to say aloud the heading, airspeed, and descent rate, and heading as it is covered in your scan. The act of saying it slows down the scan rate but will imprint it on the mind. Heading comes first always.
Always have the plane trimmed for an airspeed hands off. Any change in power (descent rate) will require trim change. Dont trim immediately on making a power change. As with other ILS corrections you will tend to overreact with power as well. When you initially change power, be prepared to immediately counter by taking off half of the initial change. Power has a delayed reaction that takes considerable experience to make the initial correct change amount. You can practice getting better at this skill by limiting changes to 100 rpm on the ILS.
Do not look for the surface on an ILS approach until you are within 100 of your personal minimums. Lock your arm and elbow before looking or you will probably need to make a heading adjustment on coming back to the instruments. At 100 above minimums, dont look too long or you will bust minimums. This is a no-no. Missed approach procedures must be commenced no later than the proper point and altitude.
You must have the correct chart when the ILS has both regular and converging approaches. the big difference will by the missed procedure and landing minimums. At present an approach can have only ONE missed procedure.
To fly the ILS you have a choice of taking the full procedure or vectors.
Either way you want to get your airspeed and configuration set before you make the localizer intercept. You use your fastest scan for the ILS final. control input is logarithmically decreased the closer you get to the airport. Heading changes outside the outer marker are at 5-degrees and 2-degrees outside the middle marker. Glide slope adjustments are made with yoke to the slightest degree. Larger adjustments by power. Full deflection of the needles call for the missed.
The ILS approach gives accurate lateral and vertical information to good runways. You get distance and altitude information that keeps you set up direct to the touchdown point. It is accuracy that permits zero-zero landings. The ILS has a variable two axis glide path that uses the localizer for lateral alignment and the glide slope for the vertical axis.
The descent is determined by a sequence of fixes and markers that advise you of distance and height. The outer marker is an altimeter setting device, distance and communications advisory point. At 200 feet you are at the middle marker and usually decision height for landing or not landing. The inner marker is being decommissioned except where lower minimums exist. One-dot on the localizer equals 500 and 50 off the glide slope at the outer marker. One-dot at the middle marker is 150 for the localizer and less than 10 off the glide slope.
Rule of thumb for ILS is to divide your ground speed by half and add a zero. It is logical to assume that any circling approach to the non-ILS runway means you will have a tailwind on the ILS and a higher ground speed than your ias.
--Fly a heading
--Initial heading changes to find the reference heading should be 5 degrees. (10 degrees only if 1/2 deflection.)
--Make all turns by reference to heading indicator.
--Stabilize your heading and airspeed based on the wind.
--Interception angle of 10 degrees maximum to the ILS.
--Set power for glide slope descent -- correct glide slope with yoke (slight changes).
--1/2 scale glide slope errors require power changes to avoid airspeed excursions.
--Power is used since yoke corrections would cause excessive airspeed changes.
--ILS Descent rule of thumb: Ground speed times five add fifty.
Flying the localizer/glide slope gets more difficult below 500' of threshold crossing height (TCH) because of increased sensitivity and visual search. If another pilot is aboard let him do the looking while you fly.
The instructor can observe how well the student is holding the airspeed and rate of descent. Changes in the rate of descent must be accomplished with no change in airspeed. Learn the skill of keeping the sound constant. As the rate of descent is less than or more than 500 fpm practice making rate changes without airspeed changes. Time the descents as well. The essence of this skill development is to control attitude and power while making small heading and vertical speed changes. This is good preparation for flying a PAR (Precision Approach Radar) approach at a military field.
An additional practice with the glide slope/localizer needles can be flown by intercepting one of the upper ghost slopes. The reason there is an intercept altitude for an ILS is that it is possible to get the needles of the ILS to function on other signals that provide a much steeper slope. Fly to an ILS runway at a high constant altitude and watch the needles. You don't usually find this in the textbook literature.
It is a good practice to initiate the descent 1/4 dot distance early. An illustrative practice of the ILS descent skill can be flown in VFR with the needles covered. At ILS intercept and initiation of the descent cover the needles and fly the descent based on the projected ground speed. Once the descent is stabilized, occasionally uncover (15 seconds) to make checks for needed corrections. A variation of this would be to establish a stabilized descent on one of the ghost slopes and fly the rate of descent with covered needles and occasional 15 second checks for performance. Once you set your known power setting for the known airspeed and known descent rate for the approach, you can control your glide slope with pitch and trim. You may find this technique much smoother and easier as a way to stay in the doughnut.
The sought for result of these training exercises is for the student to recognize that flying the ILS means stabilizing the attitude that gives the desired rate of descent and heading. When you maintain a correct approach attitude for the ILS, your airspeed and rate of descent have solved the glide slope part of the ILS equation. Scan only the AI, altimeter and needles. With a constant attitude, changes in the needles will be due to wind. If the needles move from center, first make the change required to stop the change and them make the correction. At DH take a look make your choice.
If ILS is not monitored no alternate minimums will be published. If tower is part time alternate minimums do not apply during time tower is closed. To be an alternate the procedure must be monitored and weather reporting must be available. If terminal forecast is not there use area forecast. Where nonstandard alternate minimums are published for an airport they must be used instead of the standard minimums.
ILS another way
You can fly an ILS without chasing the magnetic compass. Fly into the localizer needle when it moves; when it stops you stop turning. The VSI and CDI needle can be used as primary instrument for an ILS approach to minimums. Only fingertip pressure at all times to check the pressure of the trim setting...trim is the name of the game. Dance with your eyes over the instruments. The lower you get, the more erratic the needles and the smaller any corrections. Never go below minimums
Single Pilot ILS
When you are flying in a familiar area you become familiar with the local procedures. You know what to expect. This familiarity can become a trap.
A new controller may have a different way to do things and you may have difficulty both in hearing a clearance and in making the proper read back. Most likely you will read back what you expected to hear. You are leaving yourself open for a, "Failure to follow an ATC clearance." If you have a niggling doubt about a clearance, go for a confirmation. Your questioning a clearance takes but a moment. A sense of uncertainty can be removed by your confidence in being willing to expose yourself as being vulnerable to not being certain. Do it.
It is the ambiguities of communications that cause the problems. If you are in doubt as to the intent as well as meaning of an ATC statement, take the conservative approach and ask for clarification, a restatement or what it takes to get it straightened out. If you are asked to perform a maneuver that exceeds aircraft capability or your sense of safety, say so, and request something different. An unclear ATC clearance or directive should be considered a challenge to be accepted and corrected.
The pilot who chases the localizer and glide slope needles by jockeying the power and elevator is going to be in ILS trouble when the funnel narrows.
Cover up the AI. Have pilot concentrate on the DG, VSI, and airspeed. Set power to get the desired approach speed and descent rate. Crosswind components usually decrease with altitude.
--If you know the intercept heading is off...make your own correction.
--Dont call the airport in sight on a visual unless it is.
--You are off altitude when ATC makes a query. Fix it and then respond.
--Dont put anything on tape you dont want ATC to hear.
--Avoid shortcuts on the ground. Get help sooner rather than later.
--Take any fix short-cut offered by ATC if you can bring it up.
--If the ATC system dies, cancel IFR.
--Use everything on the panel only if you have sufficient time.
--To use everything you must think ahead and have the required time.
--When ATC gives you a heading it means that they will take care of the navigation and its time for you to the set up.:
Pre-approach Setup Order of Importance:
On an ILS set both the one and two to the ILS.
--Two needles are better than one. There is time on the missed to reset the #2.
Eight Stages of the ILS
Divide the ILS approach into eight stages, arranges priorities of when, where, and how to perform each stage.
--On downwind vector do prelanding of
--ATIS to determine minimums, runway, wind, localizer minimums.
--Altimeter setting and altitude to cross check Marker altitude
--Airspeed slowed to approach speed
--Avionics set all radios (4 to 7 depending)
--Vector to intercept. Set localizer ident.
--Set gear and flaps for glide slope descent on intercept.
--Turn--not required on ILS
--Time--only if localizer approach possible
--Twist--Set up missed approach
--Throttle--Throttle as required
--Talk--Call Marker inbound and check altimeter
--Track--Needle in doughnut and on heading
--DH + thousand feet
--Circling minimums or localizer approach option
--DH + 100 feet (Personal minimums)
--DH, have runway, have clearance, declare missed.
Fly the ILS with Rudder
Without rudder input holding headings and making heading corrections of less than 10 digress is nearly impossible. Use the rudder to hold headings and make corrections of less than 10 degrees. It's quicker, more accurate, and less likely to induce a correction back in the other direction. Sure, it's a skid, just hold the wings level and kick the rudder as required.
Fly "bugs"; "gates" and 5 degrees. Fly the localizer 5 degrees at a time by making "gate" corrections. A "gate" is the five degree space between the tics on the heading indicator. You can think of making a correctional turn on the localizer as being one or two "gates".
ILS Partial panel
With partial panel a pilot is switching views of instrument information from knowing what caused a particular event into a view of what has already happened. On Partial panel you never have the luxury of staring at a single instrument.
Flight without vacuum instruments:
--Understand flight instrument operation, characteristics and limitations
--Situational awareness by using instrument interpretation.
--Flight control using a light touch and small precise movements.
Partial Panel Is an Emergency
A pilot is expected to advise ATC of instrument and equipment failures in actual conditions. You will not receive a similar notice from your aircraft. The actual failure will be less traumatic if you, the pilot, know where you are. Situational awareness is a significant reducer of stress.
It is possible to simulate the stress of not being situationally aware by doing the following.
--Give a series of unusual attitude maneuvers with recoveries.
--During one of these when the student cannot see the panel turn the HI at least 120 degrees
--Tune in a VOR or localizer that is unfamiliar.
--Expect the student to have great difficulty both in orienting and tracking.
--Try same exercise again without the heading indicator.
--Try the same exercise again without the heading indicator on a back course localizer.
It is important that a pilot practice tracking radials and localizers using only the compass. What can happen will happen. Spatial disorientation accidents can be avoided through partial panel practice.
--Tune and center OBS needle T)--IDENT
--Bracket course. Turn to needle at first movement
--Cut time of bracket by half each time
--Use rudder input instead of yoke
--Ignore 'nervous needles'
--Practice will make process better
Losing the AI is a good partial panel exercise. The turns or lack of turns then rely on the turn coordinator or needle. Try controlling this with the rudder only. Wings level = no turn. The plane can be flown in climb, level, descent and turns without use of the yoke. It takes a lot of confidence and judicious use of throttle trim and rudder. It would be wise to know if your auto-pilot remains coupled during gyro failure so you should uncouple "George" in the event of gyro failure. The turn coordinator is the instrument of choice for recovery from unusual attitudes under partial panel.
A Better ILS
Problems related to the ILS reside mostly in faulty techniques in using the aircraft controls and lack of system understanding. We can arrive on the ILS not knowing where we are. Instead of trying to do everything at once get on the localizer established and configured before reaching the marker. Decide the DH, and MDA/Time for localizer approach as well as the missed approach procedure and initial heading. Remember, the FAF is at the intersection of the initial approach altitude and the glide slope. Set power and pitch configuration to fly the localizer descent.
--The final approach can be a hands-off affair stabilized approach if you have done the preliminaries correctly and know your airplane.
--On the localizer limit initial heading changes to five degrees. I usually put in the five and then take off half of it shortly afterwards since the tendency is to overreact.
--Make your adjustments according to your rates of descent and the heading indicator.
--Once stabilized, make glide slope adjustments by elevator and headings with rudder.
--Do not overreact to apparent large changes in the needles when close in. A large change close in is actually a small
--Remember allow zero tolerance below the glide slope. You will be high over the threshold but still have plenty of time to land.
--The ILS (Instrument Landing System) is every IFR pilot's favorite. It consists essentially of two indicators, one for "go right/go left" and another for "go up/go down".
ILS Dot Measure
Timing an ILS might well be considered a waste since before you execute the ILS missed you will be well below the Localizer MDA and any circling altitude. You have a more reliable data source than timing by using the GPS. GPS does have geometry caused errors but does not have the angular errors caused by VOR or ILS distance.
At a half-mile from the threshold, each dot is only eight feet of course error. On the ILS at the middle marker you are eight feet off the glide slope for each dot of glideslope deflection. The closer you get to the runway the less tolerance you will have from obstacles. An intercept that arrives at the marker a thousand feet high will require descents of 1500 fpm to correct a full fly down needle. Anything less may take you past the runway. A full course defection inside the marker cannot be saved unless you are visual.
ILS approaches usually are in daylight but over twice as many ILS accidents occur at night. The higher your flight time the more likely you are to fly below the glide slope. This is most likely to occur after the first approach.
ILS Safe Space
The ILS gate is one mile outside the outer marker. Protected space is 3900 to either side of the center line with 570 margin above the highest obstacle at full deflection. At one mile from the runway you have 1300 protected space to each side of the center line and 170 of obstacle clearance at full deflection of the needles.
A tailwind will have the effect of increasing your ground speed over your indicated air speed. You must adjust power or drag (Try full flaps to keep engine warm) to obtain a more steep approach than normal. You must change your numbers. The rate of descent will exceed 500 fpm. Time must be shortened. DH remains the same but a VDP should be moved away from the threshold. If there is water on the runway get slow early so as not to waste runway.
Category 1 ILS
Cat 1 operations allow a decision height down to 200' and 1/2-mile visibility and runway visual range of 2400'. 1800' RVR is allowed with touchdown and centerline lights. Even lower minimums can be allowed by using Automatic Flight Control Guidance Systems (AFCGS) Three elements are required: (1) An approved autopilot coupler; (2) AFCGS, HUD or FD must be used by pilot; and (3) Pilot must have demonstrated proficiency.
In WWII use of the term buster meant as fast as possible. Some approaches due to terrain or airspace restrictions require the 400fpm maximum TERPS descent. The downwind ILS personifies these problems. The pilot problem is remaining slow while getting down. A GPS approach with a GPS fix can solve the problem.
Be aware that ILS needles can show "perfect" approach when electrically shorted and unable to show "OFF" flags. Wise to get back-up information when things are "perfect".
Catching ILS Malfunctions
--Check approach plate for date, name, and critical data.
--Audio ident LOC during approach
--Call critical altitudes on approach
--Call marker crossing altitude and compare altimeter
--Set GPS as backup
--Monitor rate of descent to plate.
--Standard descent rate is ground speed divided by 2 plus a zero.
--Glide Slope Failure
ATC can clear a pilot for the ILS with inoperative components. ATC will tell the pilot if the glide slope is out of service. It is up to the pilot to determine if a non precision approach can be flown. If other ILS components are inoperative the ILS may need to be flown at higher minimums.
When on an ILS approach you have doubts as to your instrument indications, execute a missed approach. get a safe altitude from ATC and sort out the problem.
Was on an ILS approach where ATC had held us over a thousand feet high. Autopilot locked on to false glide slope. I was safety pilot and could see point of outer marker. There was no way the autopilot was going to make the intercept at the proper altitude. Interestingly, the instruments gave no such indication. Only a study of the plate and use of DME could have revealed the problem. At his point pilot was happy with the way the glide slope and localizer were tracking. I should not have jumped on the problem. It would have been a much better lesson to have the outer marker crossed a thousand or more feet high. If that ever happens to you, execute the missed but dont turn until the time runs out.
--Commit to memory as much as possible.
--One bar will give minimum sink flaps up.
--Use of flaps will increase vertical sink
Most ILS accidents (20-30 per year) seem to occur within a mile or less of the runway but 1/3 crash on the runway. Over half of the accidents occur at night when only 1/4 of the ILS approaches are made. Transitioning to the visual is the most demanding and dangerous part of an ILS but even more so at night. There is no margin for error in an ILS.
Runway accidents seems to be related to contact on slick runways and higher than normal speed. 1/6 of ILS accidents occur while making second or third approaches. An ATC warning of course or altitude is sufficient notice to begin the missed. Flights on the ILS to an airport known to be below minimums should be flown to DH for practice only with a planned missed. Don't fly a no-approach light ILS at night.
ILS and TERPs
ILS chart is really to approaches usually with two final approach fixes and two missed approach points. The ILS approach has a glide slope that begins when the slope is intercepted with the intermediate altitude and ends when the slope meets the true altitude of the decision height/ altitude. The Localizer approach exists when the glide slope is out. The FAF is the Maltese Cross fix and the missed approach point is usually the runway threshold. The missed approaches for both will have a mile and a half straight-ahead climbs before any turns. No turns are ever allowed before 400 feet AGL.
If DME is in the title there will be no timing table. Timing tables for the LOC approach is for the distance from the FAF to the MAP. Timing cannot be used as reason for failure when making an ILS approach during the flight test. If you should lose the ILS glide slope it is best to execute the missed rather than change to the LOC. Make the missed and shoot the LOC as planned from the beginning after confirming that the minimums will give you a good shot.
PTS for ILS
--Uses checklist and configures aircraft for conditions.
--Altitude + 100 + 10, + 10 knots
--Makes required chart adjustments to minimums and category
--Maximum 3/4 scale deflection of LOC and slope.
--Not below DH except to land
--Immediate missed at DH when no visual references.
Fly last 200' of descent on an ILS with all instruments covered except for the AI.
Best IFR aviation acronym I know is DFWTP. It's used for setting up for an ILS; configure the airplane, capture the glideslope, and then...
Dont F*** With The Power.
Failure to time an ILS is not cause for failure of test and ILS procedure.
Applies to aircraft on an ILS approach. It says that pilots are expected to remain at or above the glide slope as indicated by either the ILS or the VASI.
Rule of Thumb Compass Turns:
--Compass turns can be made by time with a standard rate of 3 degrees per second.
--When turning Northerly, undershoot the heading by the latitude in degrees plus half of the bank angle.
--When turning Southerly, overshoot the heading by the latitude minus half the bank angle.
--When turning East or West from the South roll out 5 degrees early.
--When turning East or West from the North roll out 10 degrees early.
ILS Glide Slope
Jepp gives the required descent rates for every ground speed. You can calculate the required three-degree descent rate for any ground speed by cutting the ground speed in half and add a zero. There are or can be multiple false-glide slope every 3-degrees above the plated glide slope. You can practice intercepting a false glide slope by remaining above the charted intercept altitude but on the localizer. The most positive check that you have for being on the correct glide slope is to make the recommended altitude check at the localizer outer marker. It is unlikely that you will ever intercept a false glide slope if you fly the altitudes published on the chart.
I have only once unintentionally intercepted and flown a false glide slope. This occurred when my student and I were vectored and held a thousand feet above the published intercept altitude. We were cleared for the approach while still a thousand feet high and outside the marker. My student failed to descend soon enough and we intercepted the false slope. He tried to fly the slope but in a slick aircraft the required rate of descent for the false angle was too steep so not only did we fail the get on the false slope we never had any chance of getting on the correct slope by the outer marker. We broke out of the clouds high enough for me to show the student the problem. Student has persisted in trying to fly the steep slope using his autopilot. On the missed the student was unable to make a smooth transition into hand flying.
After the flight I briefed the student that we would hand fly a larger part of each flight so as to improve his competence. It was obvious that had he performed a proper approach briefing, he would have picked up the problem sooner. The nonstandard vector completely fooled him and took me a while to notice.
The Glidepath Is Not a Glide slope
--A glide slope provides vertical guidance such as the VASI, PAPI. ILS, MLS and PAR
--A glidepath depicts the vertical descent profile of an approach.
The ILS from 200 Feet
The most hazardous phase of the ILS is the transition from the instruments to the visual approach. A major part of the hazard is related to the pilots instinctive need to descend in reaction to an illusion of pitching up. This illusion is compounded by darkness, fog, Poor visual cues at breakout can cause dangerous altitude deviations. Illusions become more likely the worse the visibility. Determining ground speed is also affected by visibility.
The angle of the ILS slope gives the pilot a projected impact point. Any change in speed or approach angle will affect this aiming point which is a hands breadth above the base of the windshield. You can use this point on the windshield as the glide slope index. the use of this point at breakout leads to illusion of a nose high attitude. At 200 feet we are dealing with the last thirty-seconds of flight.
Within 200 feet of the ground any correction for a crosswind from the left will cause the lighting give the illusion of being too high on the approach. Conversely, seeing the lights from the left will make the pilot have the sensation of being too low. All lateral flight corrections should be corrected and needle deflection contained within 1/4-scale deflection. An aircraft on a stabilized approach minimizes the effects of illusions. It is necessary that the runway approach zone be in view for several minutes for visual references be established correctly.
Approach lights give no vertical reference. Flashing lights can disorient. Any loss of reference that results in instability of the approach can be disasterous. Loss of visual reference is most likely to cause instinctive reaction to pitch forward and down. the vest security lies in having and using a VASI.
--ILS at present time is most precise lateral and vertical guide to decision height.
--Direction indications are by using localizer and glide slope needle indications.
--ILS is VHF at 150 Hz (blue sector) and 90 Hz (Yellow sector).
--Localizer antenna is 1000 feet from departure end and gives wider course than does the back course.
--Glide slope is UHF
--Antenna is at approach end of runway.
--Set OBS to inbound course prior to intercept.
--Off course on localizer shown by left/right needle deflection.
--Of altitude on glide slope shown by up/down needle deflection.
--Glide slope best flown by stabilized descent rate using pitch and power.
--Course width is 300 feet at outer marker and 100 feet at middle marker.
--Decision height at 200 feet one-half mile out.
--Use heading bug for any intercept heading front or back course
--HSI and autopilot require special procedures and knowledge..
--Getting the winds on any approach is important but vital for flying an accurate ILS
--Rule of thumb glide slope descent is five times ground speed.
--Winds tell you if a circling approach is going to be required.
--Surface winds will be weaker than winds aloft.
--Winds can determine how you make your initial intercept and initial heading.
--Proportional larger changes in power and attitudes are required when ILS is flown at low speeds.
--Opinion: Pitch for touchdown zone with 10-percent speed change only, otherwise use power.
The ILS Back Course
--Back course is mirror of front course with reverse needle sensing.
--ILS localizer has four times VOR sensitivity.
--Backcourse approximates 8 times VOR sensitivity and twice that of the front course.
--Reason for sensitivity because of antenna in front of threshold.
--The closer you get to the runway the more narrow the course becomes.
--Back course width is half of front course at the outer and middle markers. (150' and 100')
--Back course requires smaller frequent corrections.
--Important that you ignore any glide slope information on back course.
--Some ILS heads have BC or REV button to eliminate reverse sensing of needles.
--HSI may be set for or automatically eliminate reverse sensing.
--California has four back course approaches. Most are in Great Lakes region
--You will have a long runway
--GPS VNAV often exists.
--Course altitudes based on waypoints
--Usually no procedure turns
--Most require use of DME but no DME Arcs use localizer DME.
--HSI may require front setting to allow fly to needle procedure
--IFR GPS may be used but database most often does not include localizer.
Timing the ILS
--Do it only if you have the time and skill to do so.
--Any timing is done at the localizer approach FAF or marker. This is usually different than the ILS FAF
--The localizer approach FAF is an altimeter check for the ILS. The time check is for the localizer approach.
--The time is not a requirement for the ILS DA(H)
--The timing puts you over the threshold and probably unable to make a normal landing.
--Radar tracking your ILS glide slope track can warn you with MSAW when you are below the slope.
--A perfectly flown ILS will have the same indication as an ILS system failure and an aircraft system failure.
--Losing the glide slope below the MDA of the localizer requires you to go miss if it occurs before DA.
Last week I had a former student go ecstatic on me. For the first time the student was able to fly an ILS hands-off.
--Noted that when the power and trim are properly set, none of the needles move.
--When power changes, trim changes, airspeed changes, the VSI changes
If you're only off a half a dot on the glide slope indicator, you're doing well enough to pass an ATP checkride; don't mess with success. Once you get fairly close in, it will become more and more difficult to make the extremely small corrections needed to track the GS exactly. As long as you're a half dot high (as opposed to half dot low), I wouldn't do anything yet.
If you work the math (GS full scale is about 0.7 degrees above or below), it works out that each dot is about 5% too high or low. At a typical DH of 200 feet, each dot represents 10 feet of extra altitude. If you extend a 20:1 glide path from that point to the runway, that'll work out to landing 200 feet beyond the touchdown markers. Even if you crossed the theoretical MAP (i.e. about a half mile from the threshold) with a full-scale fly-down indication, you'd be only 50 feet too high, which would correspond to landing 1000 feet past the landing zone (i.e. 2000 feet from the threshold). On any runway big enough to have an ILS, landing a light plane 2000 feet beyond the threshold should pose no problems getting stopped in time. Looking at it another way, even at full-scale fly-down deflection at DH, you're still lower than you would be on a typical visual approach!
Now, clearly going full-scale fly-down on the GS at DH is NOT what you should be aiming to do, and in anything bigger than a light twin would be madness, but what I'm trying to point out is that a little bit high well within the FAF just isn't a major disaster (a little low, on the other hand, is cause for alarm).
False Glide Slopes
We know false high glide slopes are endemic to all ILS approaches. Did you know that false glide slopes have been reported below as well. All the more reason to check altimeter at intercept and marker.
ILS 28 and LOC 10 use a 'flipping of the antennae with changes of Morse code between the two approaches. Failure to identify proper code for each approach could be critical error. ATC may have failed to switch the antenna to the proper approach in use.
Return to WhittSflying
Return to IFR Contents
Continued on 7.62 All Other Approaches