We all tend to have great landings, good landings, fair landings, and every now and then, not so good landings. Sometimes, after a string of “not so good,” we rediscover the missing element and wonder how we could have forgotten a fundamental concept. Again. Just like hitting the long and straight tee shot on the golf course, a few key “swing thoughts” can help improve your landing consistency. Here are mine, and just like any good Air Force staff officer learns, things go better with three main points:
- The Slot — Vertical, horizontal, energy
- The Flare — Shifting aim point, power and pitch, nibble a descent rate
- The Rollout — Nose gear, aerodynamics, reverse and brakes
Oh, all right, just one more:
- Must Go Point — When you can (and should) safely abort the landing
Photo: E-4B landing at Offutt AFB, USAF photo, from Wikimedia Commons.
Figure: The landing slot, from Eddie's notes.
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 100 feet above the runway, 2,000 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?
The Slot — Vertical
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 VVI needle? Probably not. But twenty miles out shooting for 6,000 feet when you should be at 3,360 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:
Rule of Thumb: 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'.
Reference Flight Path Angle (FPA) Line and flight path vector
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'.
Approach Lighting System
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 and Threshold Speed.
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
The Slot — Horizontal
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?
Extended Runway Centerline
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 vertical 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.
Extended centerline on synthetic vision
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.
Figure: Lateral and vertical landing maneuver envelope, from Eddie's notes.
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. More about: Stabilized Approach.
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:
- B747 — The combination of a very large wing span induced ground effect perfectly compensates for energy needed to arrest the descent. Once the descent has been arrested, the flight idle and ground effect result in no airspeed loss at all under most conditions. The airplane has to be flown into the runway, it will not run out of speed and sit itself down.
- GV — The GV also has a very large wing span and high flight idle engines. The descent can be arrested with very little loss of speed, but the airplane does lose speed gradually if held inches off the runway. But, once again, it should be flown onto the runway to avoid a long landing.
- G450 — The G450 will lose about 5 knots in the rotation to flare, which is precisely the minimum speed increment to VREF. Once the rotation to flare is made, speed decay continues as flight idle and ground effect are not enough to maintain speed. Any exaggerated flare for the sake of touchdown will result in a significant loss of speed. Once again, the airplane should be flown onto the runway.
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. More about: Autothrottle Landing.
The Shifting Aim Point
The old mantra still holds true: “Aim point, airspeed” should be your top thoughts at this point. Your aim point is the point on the windscreen that isn’t moving. With some aircraft a heads up display might have a flight path vector indicator, which is an electronic indication of where the airplane is headed if nothing is changed. In either case, you want the aim point to be the touchdown zone of the runway unless you are flying a long body aircraft. If flying a Boeing 747, for example, your aim point should be further down the runway. That doesn’t mean you are landing further down; just that your aim point is further down. How is this possible?
Rule of Thumb: As a rule of thumb, 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. See the article Deck Angle for an explanation of this seemingly impossible rule.
If you are flying a Boeing 747, your aim point is 700 feet ahead of the actual touchdown zone. In a Gulfstream G450, your aim point is 240 feet ahead of the actual touchdown zone, so aiming for the runway 1,000 fixed distance markers will serve you well.
Photo: G450 HUD display on final approach, from G450 Aircraft Operating Manual §2B-18-10 Figure 2.
You will generally keep your aim point right on the touchdown zone. If your aim point is too far down the runway, you need to “walk it back” by increasing your descent rate slightly until it is properly aligned. If, on the other hand, your aim point is too far ahead of the touchdown zone, you need to “walk it up” by decreasing your descent rate slightly until it is properly aligned.
This is made easier with a HUD where the flight path vector eliminates any guess work on where your aim point actually is.
Photo: HUD FPA on touchdown zone, KPSM, from Eddie's HUD.
With or without the flight path vector, the aim point should be placed on the touchdown zone. On all but calm wind days the FPV will be jumping around, you just need to keep the average of its position on the fixed distance markers.
Photo: HUD FPA in flare, KPSM, from Eddie's HUD.
As the touch down zone begins to disappear, you will have to shift your aim point to the horizon. With most aircraft this typically happens about 20 to 30 feet above the runway. With the G450, putting the FPA on the horizon is usually too high, we shoot for the end of the runway.
Video: KBED - KPSM with HUD.
Power and pitch
Just about every aircraft I’ve ever flown recommended thrust reduction commensurate with pitch increase during the landing flare, so that the power levers reach idle as the wheels touch. Most aircraft also experience a pitching moment as the thrust is reduced, changing the control feel to the pilot. It will serve the pilot well to standardize the power reduction rate to eliminate changes in the feel of the pitch rotation. Auto throttles will do this nicely.
There is a school of thought that the auto throttles should be disengaged at 100' to ensure touchdown at VREF. I don't agree and believe a proper flare will put the airplane at VREF as the throttle retard motion begins at 50 feet. See Autothrottle Landing for the math behind this.
But if you insist on disengaging the auto throttles in a Gulfstream, do so only using the switches forward of the power levers, never use the switches aft of the power levers to disengage. Why? See: GIV G-GMAC.
Getting a feel for the elevator pull needed to achieve the correct pitch change is normally all pilot technique made all the more problematic as changes to aircraft weight, runway slope, ground effect, convection, and winds can invalidate normally successful strategies. Knowing how various factors can change the pitch requirements will give the pilot a leg up on these variations.
- Aircraft Weight. Generally speaking, heavier aircraft seem less prone to floating while lighter aircraft are subject to overshooting the required pitch.
- Runway Slope. If the slope in the touchdown zone is downhill the flare will have to be made to what might be an uncomfortably negative pitch. If the slope is uphill, the flare will have to be exaggerated.
- Ground Effect. On large wing span aircraft, ground effect can have a profound effect on the aircraft’s vertical descent rate while in the flare. Ground effect normally takes effect about one-half the aircraft’s wing span above the ground. A Boeing 747, for example, experiences ground effect over 100 feet in the air. A Gulfstream V, while certainly smaller, still experiences ground effect almost 50 feet in the air which high enough to impact the entire flare. If the runway sits near a cliff, the normal ground effect will be absent until the last minute, when it arrives all at once. This can lead to ballooning flare. If the runway is narrower than the wing span and the edges drop away, the normal ground effect will never materialize at full strength, possibly leading to an abrupt flare. More about: Ground Effect.
- Convection. Sometimes everything looks ideal and at the last moment things go awry for no known reason. Remember your first landing on a hot day to Runway 8L in Honolulu? The warm pineapple fields push the aircraft above glide path, so you pull the throttles back and just as you establish a healthy downward VVI to return to glide path you reach the Pearl Harbor channel where the cool waters rob you of the extra lift and now you are headed down at an alarming rate. Once you've figured that out you are over the hot asphalt of Hickam Air Force Base and the process reverses itself. What to do? Get a shot of the approach path on a terrain chart or Google Earth to anticipate any potential issues. Get on glide path early, carry extra speed if you anticipate flying from warm to cold or on speed if you anticipate cold to warm. When you hit the convection, smoothly increase or reduce power in conjunction with pitch changes. The critical thought: don’t let the convection fly the aircraft.
- Winds. While the approach happens more slowly with a strong headwind, the normal power pull may appear to drop the aircraft abruptly. With a strong tailwind, the obvious tendency is to float. In either case, auto throttles may not provide the best option. Pilots should have an understanding about how much wind the auto throttles can handle before needing to be overridden.
Figure: Convective impact on glide path, from Eddie's notes.
Heads Up Display Flare Cue
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? It is hit and miss.
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 go to the next step . . .
Nibble a descent rate.
Figure: Landing flare perspective, from Eddie's notes.
Most aircraft landing gear will absorb a 100 feet per minute touchdown gracefully and may even seem smoother than one that ends precisely at 0 feet per minute. I’ve found the most consistent landings in every aircraft from the smallest Gulfstream to the largest Boeing occur with a slight descent rate at touchdown.
By focusing on the horizon and watching the relationship of the runway edges, you can determine if the airplane is sinking, climbing, or maintaining level.
As the aircraft descends, the edges of the runway appear to rise, the angle to the horizon decreasing. The rate of the decrease provides the clue about your descent rate.
By shooting for a slight sink, you relieve yourself of the burden of estimating zero feet altitude. You will end up with an acceptable touchdown, on speed, and in the touchdown zone. The alternative method, shooting for zero feet per minute, can yield very nice results but often results in long landings or risks the nose-first miscue.
I call this “Nibble a descent rate” because it is an iterative approach. Rotate the airplane to the flare attitude and examine your descent rate by watching the movement of the lines of the runway edge. Descending too quickly? Pull back slightly and wait. Leveled off or climbing? Ease back pressure slightly and wait. Each adjustment and wait period take less than a second.
Once the main gear are on the runway continue to watch the descent rate. Make sure the main gear remain firmly in contact with the runway by easing back pressure slightly. Ensure the nose doesn’t come crashing down by continuing to fly the aircraft even after main gear touchdown.
In the following video you see the iterative nature of this technique: the pitch is changed several times until touchdown, which occurred with a slight descent rate and was perceived as a “greaser.”
Video: Landing Flare.
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.
- The B-747 has adequate back pressure available to lower the nose gently all the way down to around 100 knots.
- The GV touchdown speed is so low that you will eventually run out of elevator effectiveness and you can anticipate pulling the yoke all the way back.
- The GIII, GIV, and G450 may present the biggest challenge in the Gulfstream world, the speeds are high enough that pulling the yoke back prematurely can balloon the aircraft back into the air. Timing is important and a deliberate effort to get the nose down in a few seconds is needed.
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.
Reverse and Brakes.
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.
The Must Go Point
Every landing must be planned so as to provide adequate distance after touchdown to safely stop the airplane. If winds or pilot technique effectively botches the landing flare to beyond this point, the pilot should go around.
While normal technique calls for going around if the landing cannot be made in the normal touchdown zone, this is unnecessary when dealing with a long runway. Quite often when dealing with wake turbulence on a long runway, a long landing may actually be the desired outcome. These variations may instill in pilots a tolerance for landing long. How then to decide when long is too long?
9 ACCS Must Go Technique.
Figure: PHKO airport diagram, circa 1984, from Eddie's notes.
While flying the Boeing 707 in Hawaii, we had a requirement for touch and go landings but there were not many runways in Hawaii long enough to accommodate us. We did touch and go landings on runways as short as 5,000 feet, where an abort was impossible shortly after touchdown. Before the runway at Kailua-Kona (PHKO) was lengthened, we had only 5,300 feet to land, reset the flaps, spool the engines up, and takeoff. We identified points along the runway where an abort became impossible. These “MUST GO” points became a standard part of the pattern briefing:
“This will be a touch and go to runway 35. Land the aircraft in the first 2,000 feet and stand the throttles up to vertical. I will reset the flaps and trim and ask you to set takeoff thrust and rotate at rotation speed. At any point beyond the first perpendicular taxiway, we must go and the takeoff will not be aborted. Any questions?”
Teterboro G450 Example.
Figure: Teterboro airport diagram, from Jeppesen KTEB page 10-9.
While not many civilian jets are in the business of doing touch and go runways, we do spend a fair amount of time on shorter runways trying to smoothly land and brake to a stop. Teterboro has been host to many long landings and failures to stop within the confines of the runways.
Figure: Teterboro airport information, from Jeppesen KTEB page 10-9A.
The distance available for landing on runways 6 and 19 and significantly less than the total length of these runways because of obstacles on approach. The distance is available on Page 10-9A of the Teterboro Jeppesen Charts:
Figure: Landing data, from Eddie's notes.
The FMS provides the landing distance. In this example, the aircraft needs at least 2,350 feet to stop. Pilots would be well advised to ensure the aircraft is on the ground no later than Taxiway C when landing on Runway 6, if not, they should balk the landing and go around.
Wikimedia Commons, Public Domain Artwork