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The most reliable way to do a forced landing? High Key / Low Key

There is the Noel Kruse and his website , where he offers his (free) books about flying techniques.

In the second book, chapter Glide Circuit, he is describing his funnel procedure how to loose height and approach the landing site in the engine out scenario.

Sounds quite practical.

For comparison, what I was taught.

The underlying principle is angle de plané (AP or alpha), gliding angle, imagined as a cone under the aircraft. You find a reference point on your wing or other part of the aircraft that shows how far the aircraft can glide, which gives the glide angle α. For safety, manoeuvring is done at 2α, with α only used when you’re certain to make the field. I think the concept is the same: practise the techniques and adapt to your height and distance from the field.

PTE (prise de terrain en encadrement) or just encadrement
The ‘normal’ way of landing without power. Cross the (air)field at 2000’, turn left or right for downwind, to be abeam the threshold at 1000’. Cut the corner onto base by 45 degrees, which brings you onto a normal final. This can be calculated using geometry, but try in real life and adjust to your aeroplane. We did a downwind slightly closer than usual, but another version is to have the downwind converging at 30 degrees; I prefer the parallel method.

PTU (prise de terrain en ‘U’)
E.g. for engine failures in the circuit. At the end of downwind, a continuous 30 degree turn onto short final or the threshold. From an American instructor: “never fly patterns so large you have to tell the NTSB why you couldn’t make the field”

PTL (prise de terrain en ‘L’)
Essentially a base join, adapted

PTS (prise de terrain en ‘S’)
A straight-in join, with S-turns to lose height. The instructor said “you can also also slip, but only after the PPL test”

In PPL training most emphasis was on the PTE, with a few PTUs. ‘L’ and ‘S’ are more for low height engine failures, or when you have to change where you’re landing at the last minute.

EGHP-LFQF-KCLW, United Kingdom

Constant aspect and speed management is one way to do it, too high/close go slightly away and fly slightly slow, too far/low go slightly close and fly slightly fast

The result is a “short field power off landing”

The idea is that you want to loose energy = height+speed at touch point, at the end, you are burning energey all time: slowly when flying best glide and rapidly when flying slow or flying faster than best glide, doing it the way I describe avoids ending up high&fast or low&slow for sure

Probably too complicated? fly best glide and manage height (all what PPL syllabus want you to know) but I keep in mind there is the speed option

Best way with wind/gusts?

Calm winds, fly high and use slow speeds to burn energy: you will burn all height flying at VS0 plus few kts and unload wings any time you feel under shooting and aim for “1/4runway” while high

Gusty winds, fly high and use faster than best glide (as much as twice headwind) and slow down anytime you overshoot and aim for “1/2 runway” while fast

Basically, aim high at mid point clocking 100kts in calm days or aim at the numbers flying low at 60kts in windy day, you will do just fine

The good news is that you overestimate glide L/D when flying slow and underestimate it when flying fast, so at the end it just work !

Last Edited by Ibra at 13 Feb 13:03
ESSEX, United Kingdom

Capitaine wrote:

“never fly patterns so large you have to tell the NTSB why you couldn’t make the field

This is the theme I teach. I avoid large circuits, which increase the risk of not making your selected spot. Many pilots I have trained, particularly when landing on snow with skis, or on the water, are overly optimistic about how far their plane will glide. When they stretch the glide in the latter stage of the approach, they give up reserve energy they will really want to have retained when they begin the flare. This is particularly critical when landing a floatplane or taildragger, where touching down with too high a descent rate, or too slow can result in nose over right away. This has happened to a few friends of mine – where the total stopping distance was less than 100 feet, up side down – brutal stop!

I train my students to choose a close spot, and dump excess energy (speed) as you are assured you can surrender it. If your judgement is wrong, the bad thing is going off the end slowly, rather than stalling on, or hitting the hedge too fast. Forced approaches work out best when practiced a lot. My normal flying will have me flying an actual forced approach to a full stop landing once every four or five landings.

While holding short the other day, at an airport which is entirely surrounded by city (Oshawa, Ontario), I was delighted to see several 172’s, one after the other, announcing then flying really nice PFLs, tight, to assure they at least would get inside the airport fence if misjudged, with good slipping turns to bleed off excess speed as they turned final over the fence. It was obvious to me that from their downwind, they could have at least made it into the airport grounds, if not to a runway, so well flown circuits. and PFLs. The one consideration, which the instructors were obviously considering, is that on a cold winter day, closing the throttle suddenly can damage the engine by shock cooling it, so a partial power initial glide, with a sideslip to simulate the feel of no power. Once the engine has gently cooled, then the throttle may be closed, and a full power off landing executed.

Home runway, in central Ontario, Canada

Flying fast and unloading the wings does “stretch the glide” and give excess of speed to plan a change (at least pushing nose down does opens your eyes very early to the fact that you completely get it wrong in terms of expectations on glide ratio, headwind, thermals sink…) what you can’t do is “stretching glide” by slowing down (it is an optical illusion that does not work and if you got it wrong you will only know about it 2s from stall impact)

One will always get it wrong trying to squeeze in a short field with engine off, the real question is you wanna know the truth about reality vs expectation upfront? or at the end? I struggled a lot with doing PFLs in C172 coming from Gliders: first, I was highly optimistic on glide ratio and second, I was asked to fly rigid circuit on constant speed (irrespective of wind, terrain size), but now I am not looking to pass the skill-test, so I just reverted to my old habits: it is one of the techniques that seems to work well for me (even with no clue of aircraft best glide ratio or speed capabilities, also I am sure if it is doable yes or no at early stages on the day condition)

Btw Constant Aspect of the reference point is better measured horizon not aircraft windshield or wing

Last Edited by Ibra at 13 Feb 14:10
ESSEX, United Kingdom

Ibra wrote:

One will always get it wrong trying to squeeze in a short field with engine off,

One might, but for myself, I practice lots, and have no problem. I’ve done four actual forced landings, two of which were definitely in a short space, with bad consequences in an over run, and succeeded. With practice the opportunity to expand one’s technique increases….

Home runway, in central Ontario, Canada

I was referring more to the optical illusion of short fields: flying them on constant aspect has tendency to bring one relatively high at best glide speed (which does not work well as they are short fields), so constant aspect and slightly slower speed on backside of the drag curve may help for these, this can be done anytime to dump lot of energy excess even overhead their hedges/numbers then unload the wings and go for landing, this is how I squeeze in clam days, on windy days flying constant aspect and faster than best glide just work

Something I found useful for PFLs in clean/heavy wings where Vbg = Vs0+40kts (typical for high performance heavy gliders and touring aircraft), I don’t think it does matters for STOLs where Vbg = Vs0+10kts

Last Edited by Ibra at 13 Feb 18:31
ESSEX, United Kingdom

Ibra wrote:

so constant aspect and slightly slower speed on backside of the drag curve may help for these

How would this work power off? What could be the benefit of being slower than the optimum glide speed when the object is a safe power off landing? Yes, the plane will fly and glide at a speed less than the “best glide speed”, but if you get to the point of the flare at that slower speed, you have no reserve of energy (stored as speed, in an airplane) with which to flare. The more steep your approach angle, the more descent you have to arrest.

One of my plane’s flight manuals presents a “best glide speed” of 75 MPH, but a power off landing speed of 80 MPH. This, I have learned and confirmed from practice in the type, as a flare entered power off at 75 MPH will result in a hard landing. The plane can be glided at 60 MPH, but the wreck I bought from Fowlmere is evidence that a too slow glide will result in a destructively hard landing – you pull to flare, and just keeps going down in a mush.

I will fly a faster glide speed, particularly in a draggy plane like an amphibian, and slip off the excess speed when I know I have the touchdown zone made. And, I practice a lot….

Home runway, in central Ontario, Canada

Yes you can fly best glide all the time but my point was:

A) How do you to land safely if you arrive overhead the numbers at 200ft & 100kts with 600ft remaining runway on a 2T aircraft?

B) How do you land safely if you arrive at say 300ft & 60kts under-shooting runway by 6000ft?

Obviously, we are all supposed to be very skilled to avoid ending up in A & B but I don’t think I am really that good? So here are my answers,

For A: fly slow straight near stall for steep decent before unloading the wings and flare for landing, I beleive this burns overshoot energy quickly (maybe I am wrong?)

For B: fly fast near ground (no point pulling stick), I beleive this burns undershoot energy slowly (maybe I am wrong?), if I can’t make it, I have enough speed to move left/right before crashing

The way how one deals with A & B can be extrapolated all the way back to when engine fails (I am assuming one did already tried flaps/s-turns/sideslip/orbiting before getting to A or raise flaps/fly straight/engine restart before getting to B )

Last Edited by Ibra at 13 Feb 20:39
ESSEX, United Kingdom

Ibra wrote:

before unloading the wings and flare for landing

I don’t understand “unloading the wings” associated with a flare. Unloading the wings to me means pushing to achieve less than 1G, which is exactly the opposite to flaring for landing. When flaring, you’re trying to load the wings to create the additional lift required to arrest the rate of descent.

Ibra wrote:

but I don’t think I am really that good?

It’s excellent to be aware of your own limitations. When I’m training a pilot, if they cannot cross the threshold within 20 feet of height, and 5 knots of speed, without fiddling the power to do it, we keep practicing until they can. Period. I don’t sign off the type training until the pilot has mastered that amount of precision. When I’m crossing the trees on shore landing into a lake, I’m happy if I brush leaves. I’m unhappy if I feel (or hear) brushing trees, or think I’m 20 feet above them. Speed may be a little variable based upon winds and weight, but I would want to be within 5 knots of the target speed, that corresponds to the design requirement for GA planes. The FAA thinks I should be able to be that precise, so that’s what I practice.

A pilot’s personal level of skill with respect to forced landing precision is really up to them, and perhaps the person who might be renting them the plane. The flight manual does not provide performance values for forced landings. But if you don’t feel that you can comfortably land power off in the distance specified for the for the “landing distance from 50 feet” for th eplane, perhaps more practice is in order. Many times, I’ll land on my home runway power off from downwind, and tell a passenger: “By the way, had the engine stopped, that’s what it would have been like anyway”, so they can be more confident that engine failures are not an automatic death sentence. The point being that the landing was normal enough that it did not alarm a passenger into thinking something was out of the norm.

If it had actually quit, and I was planning to squeeze it into a tiny spot, yes, I’d sideslip, and it would be more dramatic. But when I’m planning power off from downwind, I should not need to slip it to achieve the approach and touchdown I desire.

Ibra wrote:

one did already tried flaps/s-turns/sideslip/orbiting before getting to A

If a combination of sideslip and flaps will not get you in power off, nothing short of a parachute will (and don’t get me going on parachutes) – pick a different spot. Once I have selected my spot, I will not turn away from it, so no orbiting, just S turns.

Ibra wrote:

or raise flaps

Not once they have been extended, unless you’ve magically added power to go around. Once flaps are extended, they stay extended until touchdown. I have never seen a flight manual which instructs to raise flaps during an approach, unless you’re powering up to go around. Retraction of flaps will have the plane settle so much that any possible reduction in drag is more than offset in lost altitude during the settling. And, had you been flying a slow approach anyway, and retracted the flaps, you just put yourself much closer to the [now increased] stall speed. It is wise to fly the plane as trained and in accordance with the flight manual procedures. Home made procedures are generally much less safe than flying the plane the way the manufacturer recommends…. Which is why I go to the effort to highlight posted information on pilot websites, when I can see that it conflicts with proper technique. It’s simply not fair to allow other reading pilots to think that something written might be authoritative. Fly the plane in accordance with trained procedures, and the flight manual techniques, and practice lots!

Home runway, in central Ontario, Canada
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