I believe most pilots go through their entire flying careers never really being taught how to land an airplane. The normal teaching method is little better than the pithy old saying, "The art of landing is throwing yourself at the earth and just barely missing." Hardly helpful. The way most pilots treat landings, it is an art. They get themselves over the runway, somehow, pull back the power and yoke, at some point, and judge when their wheels are just over pavement, magic.
I believe nothing in aviation has to be reduced to, art, magic, or all things unexplainable. It is a science. You wouldn't load up your airplane with the amount of fuel that "feels right" prior to a ten hour flight, would you? So let's analyze the landing with a little science. I believe this will make your landings not only safer, but more pleasing to the paying customers in back.
Photo: E-4B landing at Offutt AFB, USAF photo.
All of the illustrations about glide path on this page, except this one, are exaggerated. To understand why, consider this drawing of a Gulfstream on final approach at 1 nautical mile on a 3-degree glide path:
Photo: A view at 1 nm drawn to the correct perspective
(Notice how small the airplane is and how shallow a 3° glide path really is)
If you look very hard, you will see an airplane on the top left of the diagram. But the more important concept here is what exactly constitutes a 3° glide path. Please keep that in mind for the discussion to follow.
The airplane lands best when, moments before touchdown, it was on a three degree glide path, lined up the runway, and on a stabilized approach. The sooner you get the airplane in that slot, the easier things will be. If you consistently arrive 50 feet above the runway, 1,000 feet from the touchdown point, with a sink rate from a three degree glide path, and on speed neither accelerating or decelerating, the landing flare will be the same every time. And that is a good thing. But how do you do that?
Your vertical slot is defined on most runways to be a 3° glide path until it is time to flare:
Figure: 3° Glide Path, from Eddie's notes.
Vertically, the slot is defined by a three degree angle from the target touchdown point.
The angle equates to about 300 feet per nautical mile:
Height at One Mile = 6076 feet x tan(3°) = 318 feet
About 300 feet per nautical mile. Note there are times to be mathematically pure and times to be a pilot. Can you read 318 fpm on your altimeter? Probably not. But twenty miles out shooting for 6,000 feet when you should be at 6,360 feet might be significant. In general, however, 300 feet per nautical mile works.
So your objective is to place the airplane at 300'/1 mile, 600'/2 miles, 900'/3 miles, and so on. The sooner you are on that path, the better. While some aircraft have flight path angle indicators, most do not. You can come up with a vertical velocity equivalent.
In a G450 you might have an approach ground speed of 140 knots, which comes to:
At this speed you would travel a nautical mile in:
Your vertical velocity would be:
Like this kind of math? Check out: 60 to 1. Don't like it? Try to remember:
Descent rate on final approach is about half the ground speed times ten.
So in the G450, with a 140 knot V
You now know what you are looking for vertically. How do you judge your progress? You have several methods available to you:
ILS or LPV Glide Path — the best choices because the glide path information actually gets more precise as you continue the descent; the angle shown on your instruments are really angles and the closer to the glide slope transmitter you are the tighter the tolerances are. In the GV, for example, full scale deviation at one mile equates to about 150 feet. By the time you get to the end of the runway this same deviation narrows to 18 feet.
Figure: VNAV full scale deflection, from Eddie's notes.
VNAV (RNAV/GPS Approach) — If VNAV minimums are published and the VNAV glide path starts at the runway, this method is adequate but not as precise as an ILS, LPV, or HUD/EVS because of constant glide path deviation. In the GV, for example, full scale deflection represents 300 feet regardless of distance to the runway.
VNAV (Visual Approach) — A 300' per nautical mile target can be inserted into the FMS to provide a VNAV glide path, but this method is subject to the same constant full scale deflection problem noted earlier.
Using the 60 to 1 concept, you know that a three degree glide path should keep you 300 feet in the air for every nautical mile from the runway. At 2 nm you should be at 600', 3 nm at 900', and so on. If there is a VOR near the runway, you can figure the DME at the touchdown zone and subtract that. In the example drawing, for example, the VOR is a mile from the end of the runway.
Your FMS should also have the runway end programmed, giving you another excellent countdown of the miles to go. Just multiply the miles to go by 300'.
Figure: HUD 3° line, from Eddie's notes.
The HUD draws a line from the airplane to the ground at whatever angle you command. This angle comes from the airplane to the ground. The line it draws on the ground shows where your airplane will end up if you follow that angle.
In the following example, we are following the correct angle, but we are aimed short of the runway:
Understanding that the line comes from the aircraft and not the ground is vital to using the line to your advantage. In each of the three following examples, the flight path vector is right on the touchdown zone of the runway. So the airplane is headed to the correct spot but the angle is different.
If the line is short of the runway, you need to “walk the line up” by reducing your angle of descent. In the drawing you have raised your pitch to the touchdown zone but your flight path angle is still short of the runway. This means you will indeed land in the touchdown zone, but at too shallow an angle. You should further reduce your angle to "return to glide path."
If the line is beyond the touchdown zone of the runway, you need to “walk the line back” by increasing your angle of descent. In the drawing you have decreased your pitch so that the flight path vector is on the touchdown zone. This means you will land in the touchdown zone, but at too steep an angle. If time permits and you are above Stabilized Approach height, you should further increase your descent angle to "return to glide path."
If the line is on top of the touchdown zone of the runway, that is where you will end up if you don't flare. A proper flare consumes less than 500'.
Figure: Approach lighting system descent cues, from Eddie's notes.
You should generally be at 300' when the sequenced flashers begin and 100' at the last “Roll Bar” on a full set of ALSF-II lights. More about: Approach Lighting System.
Approach speed is often, but not always, based on 1.3 V
Any increase in landing speed has an impact on landing distance squared. Landing ten knots hot, say 130 versus 120, while only an 8 percent increase in speed, ends up increasing landing distance by 17 percent!
The standard wind adjustment is to add half the steady-state headwind and all of the gust increment, up to a certain limit. (In the G450, you always add at least 5 knots but no more than 20 knots.) This is supposed to add a margin of safety in case the wind drops and is theoretically compensated for by the decreased ground speed. It is up to you, however, to lose this extra speed prior to touchdown. More about: Landing Speed
As with the vertical component and glide path, you want to get lined up on the runway's centerline as soon as possible.
Figure: Lateral landing maneuver envelope, from Eddie's notes.
You want to have everything lined up before you get to Stabilized Approach Height and the easiest way to do that is with a good, straight-in instrument approach.
ILS, or LOC - keeping in mind the localizer is typically only accurate to 18 nautical miles, capturing the localizer beam is your best method to ensure you are on an extended centerline.
LPV - An LPV gives you "localizer performance" and in some ways it is better; it is not subject to the effects of a vehicle driving in front of an antenna and giving you full scale deflection when just seconds from touchdown. G450 Note: you should "activate vectors" prior to intercepting the LPV course, otherwise you may fail to get a vertical glide path.
VOR, NDB - these methods may be acceptable, keeping in mind they may not be coincident with the extended runway centerline.
RNAV, GPS - these methods may be acceptable, keeping in mind RNAV and/or GPS accuracy may place the instrument centerline offset or off-angle from the actual extended runway centerline.
But what if you don't have a good instrument approach available?
Photo: DU map display on final flight segment, from Eddie's aircraft.
Depending on your FMS, you might be able to draw an extended centerline from the runway to your visual approach path, making lateral alignment easy.
For more about this technique in a G450: G450 Visual Approach Guidance.
Figure: Imaginary rope, from Eddie's notes.
Getting a T-37 lined up with a small runway was never a big deal. Flying the Boeing 707 into a small runway always was. To help us with that task we came up with a few gimmicks, some just mind games, some mathematical.
Lateral alignment seemed to be problematic for some. You couldn’t turn the big Boeing on a dime and getting the airplane lined up took some practice. The drawing comes from my original notes back in Hawaii.
It seems silly, after all these years, but this is what we taught and I suppose this was supposed to help. But it is all we had to go with.
“Imagine a rope,” I would tell the younger pilot, “hanging from a pole on the far end of the runway. . .”
Sometimes the imagery would help, sometimes not.
Photo: From Eddie's cockpit.
With synthetic vision, the runway is drawn on the display with lead in lines complete with index marks. Lateral alignment is simply a matter of flying the airplane over the line.
In the real world you cannot get a ten mile final beginning at 3,000 feet AGL; you are going to have to maneuver to arrive there closer in. The key point is to know if that maneuvering will leave you in a stable condition at the latest comfortable slot position.
You should have a “no later than” stabilized approach position in mind. Most operators use 1,000 feet AGL when IMC and 500 feet when VMC. Here at Incognito Air, we use 1,000 feet above minimums for any straight-in approach, 500 feet above the runway for a visual pattern or circling approach. Keep in mind that at 500' you will be 1.57 nm from touchdown. More about: Stabilized Approach.
Prior to initiating the flare, the pilot's eyes attempt to keep the runway aim point stationary on the windshield. If the pilot does not flare, his eyes will impact the runway at that point, normally 1,000' down the runway. Because most aircraft make this approach with a positive deck angle, the wheels do not simply touchdown at their actual distance behind the pilot, but at around seven times that distance. This seems counter intuitive, but the math is explained at Deck Angle.
A G450, for example, approaches with a 5° nose high attitude on a 3° glide path. Even though the wheels are only 35 feet behind the pilot's eyes, they will touchdown 275 feet behind the aim point if the pilot does not flare.
But the pilot does flare and the round out should carry the wheels to the aim point. We practice to make this happen. The force of the engines and of gravity are driving the airplane down and forward. When you rotate the nose up for the flare, some of the energy that was used to propel the airplane forward is now used to further arrest the force of gravity. You have less force available for forward motion, your speed necessarily decreases. (I prove this mathematically below, under Flare Energy.)
If you do everything right, your wheels touchdown at your aim point and you bleed off the necessary amount of speed. And you did all of that without chopping the power violently at a height above the flare initiation point.
A view from the HUD from minimums to 50 feet:
The green airplane symbol is called the "Flight Path Vector" (FPV) and represents where the airplane is headed at that moment. The horizontal line going through it is a "Flight Path Angle" (FPA) and shows that we are on a 3° glide path that intersects the runway at that line. Notice that despite the gusty winds I have kept the FPV and FPA on the 1,000 foot fixed distance marker, my aim point. That isn't where the wheels are headed, they are headed about 300 feet short of that, just after the 500 foot fixed distance marker.
Photo: HUD FPA on touchdown zone, KPSM, from Eddie's HUD.
The rotation-to-flare requires energy to arrest downward momentum; the amount of energy required depends on the glide path angle, any differences in aircraft speed from target speed, and any acceleration/deceleration. It will be to your advantage to make the angle and speed differences the same for every landing.
The rotation-to-flare may or may not bleed airspeed, depending on aircraft flight idle and ground effect characteristics. Here are three examples:
The target speed should consider wind, usually adding half the steady state wind and the full gust increment. In the GV the additive is a minimum of five knots and a maximum of twenty knots. The GIV uses a ten knot minimum. In most cases, however, you need to bleed this additive off before touchdown.
The key point here is that if you do not have the required energy prior to flare rotation, you may not have the ability to flare properly at all without adding thrust. If you find yourself in a last minute sink rate, for example, the correct solution may be to land without reducing power until touchdown. Very few aircraft should land with the power cut above the flare. Every aircraft I've flown that was certified to land with the autothrottles providing the retard in the flare lands best doing just that.
Very few manufacturers specify a flare height. Gulfstream, for example, leaves you off at 50 feet and the next thing you know, you are in the touchdown zone. Some Bombardier manuals say, "at or below 50 feet." About the only manufacturer that does print a height is Boeing. In their Boeing 777 Flight Crew Training Manual, they say this: "Initiate the flare when the main gear is approximately 20 to 30 feet above the runway by increasing pitch attitude approximately 2° - 3°. This slows the rate of descent." That pretty much agrees with what we did in the Boeing 747.
The Boeing recommendation has worked for me in every Boeing, Challenger, and Gulfstream I've ever flown. By "work," I mean it gives me enough time to complete the flare and still land in the touchdown zone:
A view from the HUD from 50 feet to 20 feet:
You should, of course, consult your manufacturer's books. If the books are silent on the subject, find a mentor who seems to land consistently in the touchdown zone and see what he or she is using. If you don't have anyone with such a track record, spend some time in the simulator. I am betting the answer will be between 20 and 30 feet.
Once you have your answer, try to be consistent. Now this flare height isn't going to work if you find yourself descending at over 1,000 fpm approaching flare height, obviously. So don't do that. Have a consistent 3° glide path on a steady speed and flare at your chosen height. Every time.
I tend to use the radio altimeter's announcements. At "thirty" I get ready, at "twenty" I flare. But what if you don't have that? In some flight schools you are told to flare when your aim point disappears below the nose, but that is ridiculous since your eyes will impact the runway looking at the aim point if you don't flare. I recommend you start the flare when the point the wheels are pointed at disappears below the nose. How do you find that? To answer that question, let's look at a Boeing 747.
The Boeing 747 flight manual says if you are on a 3 degree glide path with a 5 degree body angle, when your eyes are 52 feet above the runway your wheels are only 10 feet above. In this position your aim point is 1,000 feet down the runway but your wheels will touch nearly 700 feet earlier. The airplane is 225 feet long and the body gear is 114 behind the nose. Clearly the math isn’t simple addition and subtraction.
In a three-point attitude, the pilot’s eyes are 27 feet above and 100 feet ahead of the main landing gear wheels.
Illustration: B-747 in a 3-point attitude, from Eddie's notes (B-747 from Julien Scavini, Creative Commons)
When in an approach attitude, the aircraft angle — what 747 pilots call “deck angle,” is 5 degrees nose high.
Illustration: B-747 in approach attitude, from Eddie's notes (B-747 from Julien Scavini, Creative Commons)
Some Boeing 747 manuals specify that the geometry of the approach at 1,000 feet from touchdown will place the pilot’s eyes 52’ above the runway.
Incredibly, if the pilot doesn’t flare, the wheels will touchdown 992 - 305 = 687' behind the aim point! I've duplicated this math on smaller aircraft and a general rule of thumb appears to work:
The main gear will touchdown behind the pilot’s aim point a distance seven times the distance between the pilot and the main gear, plus flare distance.
So we can surmise that the point at which the wheels are "aiming" is seven times the distance between the pilot and the main gear behind the pilot's aim point. In the case of the Gulfstream G550 in the video above, the main gear are 45 feet behind the pilot's eyes. So we an estimate the main gear "aim point" is 7 x 45 = 315' behind the pilot's aim point. If you look at that video, you can see we arrive at the "twenty" foot radio altimeter call just over 400 feet from our aim point.
I have long taught that if it takes you longer than 4 seconds to flare, you are doing something wrong. Holding the airplane off so that the time from flare initiation to touchdown longer than 4 seconds means you are consuming runway not planned for in your manuals. But does the math support that?
Using a 25' flare height, 125 knots, and the G550's 45' distance from the main gear to pilot's eyes:
Photo: G550 flare distance, assuming 125 knots and rotation begun at 25'
Click photo for a larger image
d = 25 / tan(3°) = 477 feet
f = 7 (45) = 315'
A view from the HUD from 20 feet to touchdown.
So how do we flare in 4 seconds?
Photo: HUD FPA on touchdown zone, KPSM, from Eddie's HUD.
Your aim point up until flare height has been the touchdown zone. As we have seen, if you don't flare the wheels will impact the runway considerably short at an unacceptably high touchdown rate, between 600 and 700 fpm. You want to raise the nose so as to break that descent and place the wheels in the touchdown zone at a reduced rate of 100 fpm. To do that, raise your aimpoint to the end of the runway.
Photo: HUD FPA in flare, KPSM, from Eddie's HUD.
If you made everything else consistent (aiming at the proper point and descending along a 3° glide path, you should be able to consistently time your pull back so that 4 seconds after initiating the flare, the wheels will touch. If you don't have autothrottles with an approved landing flare "retard" function, try pulling the throttles from their approach setting to the idle stops in that same 4 seconds.
Figure: Convective impact on glide path, from Eddie's notes.
Some aircraft heads up displays offer a flare cue that provides hints as to (1) when to begin the flare, (2) at what rate to rotate the pitch, and (3) how to complete the touchdown. It has been my experience that the Gulfstream flare cue does the first two items well. The third item? I think it has you raise the nose too high, resulting in a late touchdown.
Figure: Landing flare cue 100 feet from Eddie's notes.
With the G450 PlaneView system, the flare cue appears at the bottom about 100 feet AGL. In this example, the flight path vector is over the touchdown zone:
Figure: Landing flare cue catches wings, from Eddie's notes.
The pilot should maintain the flight path vector right where it is and wait for the flare cue to move upward and “catch” the wings. At this point the pilot begins the flare rotation:
Figure: Landing flare cue horizon, from Eddie's notes.
Here the manual has you increase the pitch as the flare cue rises, finally to end up with the flight path vector on the virtual horizon, meaning level flight. We've found over the years this tends to be too high and will result in a long landing.
In an ideal world all this works out perfectly. In a less than ideal world, sometimes it works and sometimes it doesn’t. We’ve seen the flare cue level off a foot above the runway to drop the airplane with a thud, or less often flare too late for a bit of a bounce. Even the good landings tend to be a little long. I recommend following the flare cue to about the end of the runway and then maintain that gentle 100 fpm sink rate.
Your approach might be impacted by a crosswind, your flare will be, but not necessarily the way you have been trained. There are three basic methods:
Figure: B-737 touchdown in a sideslip, from Eddie's notes.
This is what most pilots call the "wing low" method and is familiar to many because that is the usual method taught in primary aircraft. It is perfectly acceptable in most Boeings but not so much for many business jets.
Figure: GV wing tip clearance in a 3-point attitude versus 5° nose up, from Eddie's notes.
Looking at your aircraft in a three point attitude may lead you to believe it will take a lot of bank to get the wing tip in a sideslip landing. If you have a swept wing, the look of things can be deceiving. In a GV, for example, the wing tip is actually lowered 17" when the nose is raised to a normal flare attitude.
More about this: Flight Math / Wing Tip Hit Bank Angle on Landing.
Figure: GV bank angle to hit a wing tip in a 3-point attitude, from Eddie's notes.
In a 3-point attitude, if you were able to push the aircraft over on a wheel, the wing would contact the ground at 7° of bank:
Figure: GV bank angle to hit a wing tip in the landing attitude, from Eddie's notes.
Figure: B-737 touchdown in a crab, from Eddie's notes.
This method also works for some Boeings but I don't think it works for any Gulfstream because the side loads on the main landing gear would be too great.
Figure: Decrabbing a B-737, from Eddie's notes.
This method is a combination of the two previous: you approach in a crab and at some point prior to or during the flare, you press downwind rudder to align the nose of the aircraft with the runway and opposite aileron to stop any drift. Manufacturers generally agree this will be done during the flare.
Some Bombardier manuals, for example, say "as the flare is commenced, application of rudder is used to align the fuselage parallel with runway centerline." Some Dassault manuals agree, saying, "during flare, apply rudder to decrease the crab." Gulfstream says, "approaching touchdown, the rudder is applied to align the aircraft fuselage with the runway and simultaneous opposite aileron is applied to achieve zero drift."
For more about crosswind landing techniques, see: Crosswind Landing.
There are two common methods for adjusting approach speeds to deal with wind gusts. The most common is used by Gulfstream:
[G450 Airplane Flight Manual §5.11] If gusty wind conditions are present, add ½ of the steady state wind plus the full gust value to a maximum additive of 20 knots (VREF + 20). VREF will still be the target speed at the threshold.
Another method is used by others, such as Dassault:
[F900EX CODDE2, ] Approach speed (VAPP) is the result of: VREF + wind correction. For wind correction (maximum 20 kt): apply half headwind + full gust increment. COMMENTS: The gust value should be taken into account whatever the wind direction is. For example for RWY 18, wind 120/20G30 given by the ATC: the steady state headwind component is 10 kt (crosswind component is 17 kt) and the full gust is 10 kt so the wind correction should be 15 kt (which is less than 20 kt).
So one method is half the steady wind and all the gust, the other is half the headwind component and all the gust.
There is a willful blindness about this from our manufacturers in that (a) you need a margin over stall speed to flare and that is typically 1.3 but can be as low as 1.23, (b) the landing performance numbers are based on touching down usually at that number but in some of the Boeings I’ve flown was based on that number minus 5 knots, (c) the gust additive is designed to protect your margin above the stall, and (d) everyone says you the pilot are responsible for using the additive and yet touching down on speed.
My philosophy has been to use the additive, carry the additive all the way, and plan on performance numbers landing hot by the additive. If the runway is too short to land VREF+20, then I need to find another runway.
More about this: Gust Additives.
"How" you touchdown is a matter for the manufacturer, but in general, I find the following ideas helpful:
Figure: Touchdown relative wind, from Eddie's notes.
Most aircraft enter the flare with a nose up pitch and positive angle of attack on the wings. The relative wind hits the wing bottom first, having the effect of pushing the nose of the aircraft upward. As the main gear touch, the momentum of the aircraft continues downward and the aircraft tends to pivot around the main gear, throwing the nose gear downward. If the pilot does nothing with the pitch controls, the nose will on its own slam onto the runway. As the relative wind moves from underneath the wing to above it, it adds to the downward force on the nose. Momentum and the relative wind work together to slam the nose earthward. The pilots must exert increasing back pressure after main gear touchdown.
The difficulty of gracefully lowering the nose to the runway varies with aircraft.
You need to understand the forces of nature are against you when it comes to going from a two point attitude to three. You need to anticipate the need for more and more back pressure. If you land with the airplane in proper trim you will need back pressure as the relative wind hits the top of the wing, more back pressure as the nose starts to fall, and, at least with the G450, the yoke will end up near your lap as the nose wheel finally touches.
As the aircraft decelerates you will need to increase aileron inputs to keep the wings level until the aircraft is in a three-point attitude. You need to get the airplane into a three point attitude before you lose rudder effectiveness and the point this happens probably is not VMCG. VMCG is a number required for certification but the published number only works for a set of conditions of the manufacturer's choosing, it could very well be much higher or lower. More about that: VMCG Minimum Control Speed Ground.
You will need to increase rudder inputs to keep tracking runway centerline. On aircraft with rudder pedal to nosewheel steering interfaces, knowing the mechanics will help with understanding when rudder is more important than nosewheel steering, and vice versa. In the G450, for example, there is a one second delay after nosewheel touchdown before steering inputs are started and nosewheel steering inputs are limited to 7 or 8 degrees. More about that: G450 Rudder.
On aircraft with true clam shell reversers, such as the GIII, reverse thrust is aimed forward and is fairly effective from high speed to medium speed ranges. Aircraft with cowl “cascade” reversers, such as the Boeing 747 with C-6 engines, aim the reversed air outward and act as very large speed brakes. This type of reverse is only effective at high speeds and is practically useless at medium and lower speeds. Some aircraft with hybrid systems, such as the Gulfstream V, are mostly effective at high speeds with little impact at medium and lower speeds.
Regardless of reverser type, the best impact is at high speeds and it is to the pilot’s advantage to use as much reverser as possible as soon as possible. The axiom “by the time you know you need them, it’s too late” is true with reverse thrust. For a case study about how not to use reverse thrust, see Southwest Airlines 1248.
Boeing 737 NG Flight Crew Training Manual, Revision 12, June 30, 2013
Dassault Falcon 900EX Crew Operational Documentation for Dassault non EASy (CODDE), Dassault Aviation, March 26, 2010
Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013
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