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Vfr screen height

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Vfr screen height

Old 19th Feb 2021, 18:57
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Vfr screen height

All,

unfortunately long forgotten and canít find any reference. Is there a screen height requirement for light GA aircraft? Airmanship aside, do I have to cross the departure end of a runway at 50ft? I know according to CS 23.53 manufacturers have to supply take of data to 50 ft but do I actually have to cross the dep runway end at that altitude or do I only have to make sure the ground run falls within the TORA. Any references would be appreciated.

thanks in advance
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Old 19th Feb 2021, 19:43
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Take-off to 50' data is to allow for obstacles. There are many strips where few aircraft are at 50' when they pass the end of the runway. Aircraft manuals usually also give ground run required.
it's the pilots privelege to decide if the runway is suitable.
(I'm much more cautious since I aborted and hit a fence 27 years ago - uphill, long grass, near max AUW, but into wind, with telephone wires in the distance.)
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Old 19th Feb 2021, 19:50
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Thanks for the quick answer!

indeed my initial question was lacking. Performance data supplied is distance for the ground run and distance to clear a 50 ft obstacle. I was having a discussion with someone wether there is a legal requirement to cross the runway end at 50 ft or, as long as your ground run is less than the runway youíre legal(no specific alt over runway end).

again, airmanship aside, just interested in the legality.
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Old 19th Feb 2021, 21:18
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FAA Part 23.2115 requires the OEM to demonstrate and provide take-off performance, ground roll and distance to 50í. Also, in the initial climb configuration demonstrate a 8.3% gradient, no final altitude required.

I donít see any 50í at the TORA requirement, itís very different from Part 25. Still have meet the 35í requirement, if itís an IFR flight for obstacle clearance, it that is a TEEPS or PANS-OPS requirement, not certification.
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Old 19th Feb 2021, 21:39
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Part 23 and below are 15m / 49ft

Part 25 is 10m / 35ft.

They are certification requirements for declared TODR.

They are mandatory minima for public transport planning, they are recommended for non public transport planning. I don't think that changes much as you cross the Atlantic. Legally for a private flight you can use TORR, or frankly press your luck and hope your handling skills are amazing, then explain it to the insurer later.

Europe does add additional safety factors (1.3 for take-off, 1.43 for landing) which are not used in FAAland.

If there's a separate rule for IFR departures I missed it in my EASA and FAA IR courses, but I may have done.

G
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Old 19th Feb 2021, 22:39
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A licenced aerodrome is required to publish data which includes the actual dimensions of runways and the safe areas around it. At the sides of the runway is a sloped area which must be clear of all obstacles. Nothing that protrudes into it is allowed. At each end of the runway there is also a sloped area that extends and must also be clear of all obstacles. The point at which it is guaranteed to be clear of an obstacle at 50 ft (TODA) is also published. The required slope to avoid an obstacle may have to be moved back shortening the actual runway. So the TORA (take off runway available) may be less than the actual runway dimensions because of this. The aircraft must be capable of lifting off within the TORA and be able to climb above the slope to avoid the published obstacle. Conversely the approaching aircraft must be able to descend above the slope and arrive above the threshold at 50 ft (the screen height): this allows for such things as the undercarriage. It may be necessary to displace the threshold to comply with the slope, shortening the landing runway. From the landing threshold to the end of the runway is the landing distance available (LDA).

The same standards are also part of the aeroplane approval. the take off ground run required and the take off distance (the point at which the aircraft can achieve 50 ft height gain. Obviously these will vary according to the aircraft weight, runway surface, slope, air density and wind velocity. The manual must provide the means to calculate this. The aircraft manual will also give the means to calculate the landing distance which is from 50 ft above the threshold to the point that the pilot can reasonably be able to bring the aircraft to a halt with normal braking. This will need to be factored of course as with the take off.

If you want to study this in detail then the reference is: UK CAA CAP 168 'Licensing of Aerodromes'. For the aircraft performance study the manual.

Last edited by Fl1ingfrog; 19th Feb 2021 at 22:53.
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Old 20th Feb 2021, 06:35
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Hi Fl1ngfrog,

thanks. I believe licensed in EASA means runway, hardened, 800mtrs or longer with an instrument procedure(but I may be wrong). Concur with your writing but it does not answer the question(I think). Does a GA aircraft flying VFR under EASA part NCO have to comply with specific performance? The only thing I can find is you have to operate within mass and balance restrictions and the performance has to be adequate for the operation. Nowhere can I find a reference that the airplane has to cross the DER at 50’ on take off.

I always understood it to be as galaxy flyer and genghis said.

Greetings
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Old 20th Feb 2021, 08:36
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I believe licensed in EASA means runway, hardened, 800mtrs or longer with an instrument procedure(but I may be wrong).
No, there are lots of licenced grass runways throughout Europe and many runways below 800 metres. Netherthorpe Airfield (EGNF), Sheffield is a licenced aerodrome. It has two grass runways: 06/24: 553 metres and 18/36: 382 metres.

Nowhere can I find a reference that the airplane has to cross the DER at 50’ on take off.
No such regulation exists. If the aeroplane can perform better than the published minimum safe operation for a particular runway then you should do that and this is expected. How to calculate the minimum take off roll and the total distance to achieve 50 ft, for various conditions, is found within the aircraft's Flight Manual/POH.

Last edited by Fl1ingfrog; 20th Feb 2021 at 12:03.
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Old 20th Feb 2021, 12:39
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Answering this question:

Airmanship aside, do I have to cross the departure end of a runway at 50ft?
as asked:

If it mean that you're asking if you should climb to 50 feet when there is no obstacle to clear, I would reply certainly not, if doing so means an initial climb at a speed slower than Vy. A Vx climb is a safety compromise in EFATO to get you over an obstacle. Do not climb at Vx if you do not need to do so for actual obstacle clearance reasons. Of course good airmanship, and neighbourly piloting is nice, but not at the expense of safety.

A single engined GA plane probably cannot glide back to a safe landing after an engine failure at 50 feet and VX, so why be there needlessly?
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Old 20th Feb 2021, 17:54
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Originally Posted by Pilot DAR View Post
Answering this question:

A single engined GA plane probably cannot glide back to a safe landing after an engine failure at 50 feet and VX, so why be there needlessly?

Seriously ? Glide back after an engine failure ??? At 50 feet ????
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Old 20th Feb 2021, 20:02
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"Seriously ? Glide back after an engine failure ??? At 50 feet ??"
Back to the surface, with enough speed to round out and land
As opposed to damaging stall or nose strike.
Was the Tiger Moth demonstrated as safe to stall in from higher than that, as a sales promo by Geoffrey de Haviland?
The reason not to climb steeply at the start of glider winch launches, especially with the knotted wire we used 60 years ago.
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Old 20th Feb 2021, 22:57
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Making 50 ft a priority when there is no obstacle to overfly is unnecessary I agree. I don't understand the objection though to using a 'best angle' climb (VX). All pilots should have been properly trained to do this safely and at many airfields due to obstacles it is the standard practice.

All that you need to know; runway dimensions and TODA etc is known before you leave the club house plus, of course, the aircraft capability. All this stuff is made available to ensure the take off is predictable and possible without exceptional skill. The best advice, in my view, is never turn back from the climb out following an engine failure.

... is a safety compromise in EFATO to get you over an obstacle.

The 'best angle' climb (VX) gets you to height in the shortest distance. The 'Best rate' climb (VY) gets you to the height in the shortest time. The VY climb provides the better options in the event of a EFATO in my view.
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Old 21st Feb 2021, 01:12
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Some comments, if I may.

The original 50ft screen goes back to some US military demonstrations (Curtiss, as I recall) a very, very long time ago .. The demonstrations were at a military parade ground (I didn't get the specific location in the original tale from an ancient Aeronautics Branch/CAB engineer) but the area was surrounded by trees of around 50ft height. As with a lot of initial civil rules, TLAR ruled much of the decisions in those days.

The heavy 35ft screen will date to the ICAO report on performance in the 50s - I would have to dig it out to locate a specific reference - there was a number of changes introduced around that time to accommodate the piston to jet transition period. 50ft screen, though, continues for the lightie brigade.

So far as compliance with things might be concerned, I presume that most jurisdictions will have a requirement similar to Australia's CAR (1988) 138 which says that a pilot must comply with the flight manual requirements. While I have no legal competence, that probably means at law that, if the flight manual says you require a certain TOD, then you need to operate from strips with not less than that distance on the day. How the pilot actually should manipulate the aircraft may have some guidance in the flight manual but, I suspect, if the pilot chooses to fly over the far fence at a low height (eg in a light twin to get some extra speed for the possibility of a failure) then that might be subject to post mishap discussion both at law and with the insurance company ?

In respect of the OP's question, I doubt that there would ever be any sort of rule which might seek to impose a requirement to cross the end at 50ft - in general, we would be significantly above that level for most runways, depending on what might be built into the flight manual performance data for a particular jurisdiction NAA.

Be wary of quoting TORR/TORA data as that really only is used for heavy aircraft performance work. TODR/TODA is the more relevant metric for lighties.
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Old 21st Feb 2021, 03:22
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Seriously ? Glide back after an engine failure ??? At 50 feet ????
I don't understand the objection though to using a 'best angle' climb (VX). All pilots should have been properly trained to do this safely and at many airfields due to obstacles it is the standard practice.
Sure, the plane is capable of climbing away at Vx, and that is a required pilot skill. But the part of the training which is (and nearly always has been) missing is that a low altitude engine failure at Vx can have you in a situation from which a gliding return to a safe landing is not possible. I've done the certification flight testing for this requirement, and it's terrifying!

So, to practice safely (before you assert that I'm wrong), try the following: Establish a safe hard deck for yourself, a few thousand feet up in the practice area. Do your HASEL check ('cause you're probably going to need it!) Slow the airplane at cruise power to Vx at exactly that altitude. Apply takeoff power, and climb from that altitude while maintaining Vx. At 50 to 100 feet, close the throttle. Now you're going to have to push the nose down fairly promptly to enter a glide, But, because you were actually expecting this, delay one second before you push to make it more realistic. Now establish the POH glide speed, and then, while referring to the altimeter, and leaving the throttle closed, momentarily arrest your descent at your hard deck altitude, just long enough to see the altimeter pointer pause there. If you can pause the altimeter there long enough to see that you did, you succeeded in a simulated flare and landing. If the plane just stalled, and kept on down through your hard deck, you crashed.

When I teach this, nearly every time, my student will descend unarrested through the hard deck altitude, with the stall warning blaring. Understand that generally, Vx is somewhat slower than the glide airspeed you'd like to have when you go to pull to flare. 50 to 100 feet is not enough altitude to push over, accelerate to glide speed, and still have altitude to spare to flare with. In my opinion, it is a serious omission that flight manuals do not contain this warning. Rather, they usually say words like: "lower the nose and accelerate to Vy when the obstacle is cleared". So, if there's no obstacle, don't be flying at Vx in the first place.

The design requirements for many GA planes do not require that a glide landing be possible from Vx. When applicable, the requirements ris that a glide landing be possible from Vx + 5 MPH:

(my bold)

Sec. 23.51

Takeoff.

...................
(2) Upon reaching a height of 50 feet above the takeoff surface level, the airplane must have reached a speed of not less than--
(i) 1.3 ; or
(ii) Any lesser speed, not less than VX plus 5 miles per hour, that is shown to be safe under any condition, including turbulence and complete engine failure;
Any GA planes for which I've looked it up, have a Vx which is noticeably slower than the best glide speed. In a draggy plane, the effect suddenly slowing down with sudden power loss is greater.

If you need to climb at Vx to make it out, certainly do that. If you don't need to be at Vx, Yv, or best glide speed for climb will keep you safer. And remember that the best glide speed is predicated on an engine failure in cruise flight, when you're level, and you slow to that speed, rather than shortly after takeoff, and you have to lower the nose that much more to speed up to that speed, and still have enough altitude with which to glide and flare. This should be practiced by all single engine pilots - at a safe altitude!

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Old 21st Feb 2021, 12:13
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Pilot Dar makes his arguments convincingly but this issue is yet another of those, to which there is no final answer, that satisfies everyone.

85% of aircraft accidents are due to the pilots actions and are not a mechanical failure. Some years ago I was part of a private visit to the AAIB at Farnborough. Serious accident aircraft were laid out in a hangar. The Accident Investigator hosting, stopping at one twisted and mangled assembly, commented: "the tragedy here is not the engine failure itself but the actions of the pilot before and after the failure.

It is a luxury at small airfields to have sufficient runway remaining, during the take-off, to be able to land back on and stop. Obstructions are also often ahead that require a VX climb. At these airfields accidents rarely happen to base operators. Anecdotally, they tell me, and in my personal experiance, that the skills of visitors from much larger airfields are shocking: a poor understanding of short field/soft ground techniques and an inability to climb at VX safely and accurately. Approach speeds are typically uncontrolled and too fast and go around decisions, being mainly a reaction to the looming boundary fence, made too late. All these things are bread and butter for the base operators and provide for safe flying.
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Old 21st Feb 2021, 13:20
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For my experience, in GA planes, at aerodromes where obstacle clearance could be a factor, there is rarely authoritative information about the dimensions. For aerodromes/airports which do publish those numbers, there's usually ample space for GA operations at Vy or faster, obstacle clearance performance/technique is rarely necessary.

Where obstacle clearance technique becomes important is at aerodromes (or other places) where there are obstacles, and the dimensions (takeoff distance available and obstacle height are not stated. The airplane manufacturer has provided performance information to fulfill certification requirements, but it's rare that it's exactly those combinations of dimensions, when you really do need to know. If, at the non published dimension aerodrome, you can acquire measurements, that's great, and I have used Google Earth for this purpose. Often, it's simply a judgement, with a conservative go/no go point along the takeoff run.

When I train this, I train the student to simply clear the obstacle with the greatest airspeed, and a lesser clearing altitude. I'd rather see the extra 5 knots of speed crossing the obstacle, than an extra 100 feet over the obstacle. If the speed was not at least Vy crossing the obstacle, the extra 100 feet really did not help you much if it quit. You'd use it up simply getting back the 5 knots you could have had anyway. For the few runways I have used where very tall trees (100 feet) were a certain obstacle (at the very end of a 1500 foot runway), I have disciplined myself to aim at the 2/3 height point of the trees, and accelerate toward that point as though I'm planning to ram the trees, and then smoothly pull up over them in the last few seconds, momentarily trading speed for altitude only as needed. I practice this in my own home runway, as I go out between 60 foot high trees right at the end of my runway. But my very ind neighbour let me cut down the obstructing ones 30 years ago when I purchased the property. I have a good reference for obstacle clearance technique, with lower risk while practicing.

Obstacle clearance takeoffs are sometimes required in smaller runways, and are commonly required for water takeoffs, as it is very common for a lake to be bounded by trees, and perhaps hills. And your takeoff path on a lake is very much less likely to be accompanied by dimensions (hence preplanning with Google Earth in recent years!)
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Old 21st Feb 2021, 15:30
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Obstacle clearance takeoffs are sometimes required in smaller runways, and are commonly required for water takeoffs, as it is very common for a lake to be bounded by trees, and perhaps hills. And your takeoff path on a lake is very much less likely to be accompanied by dimensions (hence preplanning with Google Earth in recent years!)
In the UK of course there are many fields that fit your description. However, for decades it had been required that ab initio training must be done from a licenced aerodrome. Therefore all the parts of the international airport licence also formed the same for even the smallest of airfields where training took place. These airfields have an ATZ and are required to have a detailed survey. They are also a statutory consultee for planning purposes. Obstruction data was therefore always up to date.

Since EASA training aerodromes are no longer required to be licenced but most have retained their licenses for the benefits and protections it brings.
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Old 21st Feb 2021, 19:10
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Actually, I think nearly 100 previously licensed aerodromes in the UK promptly gave up their licenses as soon as the outbreak of common sense occurred. The UK CAA were glad to be relieved of the burden of having to visit them all and to concentrate on the ones that need licensing, i.e. those with public transport undertakings.
What the legacy of these previously licensed aerodromes provides is an environment that is substantially the same as meets the criteria for flying training as per CAP 793. This is rather different from the microlight training environment, which has never been required to operate from an aerodrome with essentially public transport limitations.. This is great for base operators (as above) but a bit tricky sometimes for visitors.

TOO
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Old 22nd Feb 2021, 13:23
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Well, from a simple question that was correctly answered in post 2 this thread has really gone off the rails.

Originally Posted by Pilot DAR View Post
Understand that generally, Vx is somewhat slower than the glide airspeed you'd like to have when you go to pull to flare. 50 to 100 feet is not enough altitude to push over, accelerate to glide speed, and still have altitude to spare to flare with. In my opinion, it is a serious omission that flight manuals do not contain this warning. Rather, they usually say words like: "lower the nose and accelerate to Vy when the obstacle is cleared". So, if there's no obstacle, don't be flying at Vx in the first place.
Nobody is saying to climb at Vx if you don't need to. But Vx is a safe speed to flare from. There is no need to accelerate to best glide, let alone Vy, for a safe flare. The 50 foot speed in a max performance take-off will be equal or less than Vx and yet it is certified “safe under all reasonably expected conditions including complete engine failure” and “not requiring undue skill”. References below.

Vx is somewhat slower than the glide airspeed you'd like to have when you go to pull to flare
I don't know where you are getting this idea that it is better to flare from best glide speed, whether that be an EFATO or any other forced landing. The best glide speed gives you best glide range. It does not follow that best glide speed = best flare speed. If you have an engine failure at 50' it is hardly likely that you will need to prioritise range over minimum landing distance. Best glide is unnecessarily fast for a flare when you are in danger of running out of space to get the aircraft stopped. The glide speed I "would like to have" is the one recommended for engine failure, so here are some POH figures:

C-172: glide 65kts; landing without engine power 60kts. (Vx = 59)
PA-28: glide 73kts; “when the field can be easily reached slow to 63 knots for the shortest landing”. (Vx = 63)
M20K: glide 90kts; EFATO 75kts flaps down. (Vx = 79)

...high wing, low wing, and high performance, so fairly representative of the pisotn single fleet. Recommended power-off landing speeds less in each case than best glide. All certified and approved by authorities worldwide. NB the following certification requirements and guidance regarding the 50 foot speeds:

shall be an airspeed not less than 1.2 VS1 or VS1 plus 10 knots, whichever is the greater, at which adequate control is available in the event of sudden complete engine failure during the climb following take-off ....Take-off techniques should produce consistent results and not require undue skill or strength on the part of the pilot. [CASA Part 21 FTG]

speed and height sufficient to ensure capability of performing all maneuvers that may become necessary for safe completion of the takeoff and for safe landing if necessitated by power failure. An airspeed margin above stall in conjunction with a height of 50 feet is presumed to assure the desired maneuvering capability.....The procedures used for determining takeoff and landing distances must be executable consistently by pilots of average skill [FAA CFR 23 and AC23-8]

A speed that is shown to be safe under all reasonably expected conditions, including turbulence and complete engine failure [EASA CS23]
A single engined GA plane probably cannot glide back to a safe landing after an engine failure at 50 feet and VX
Based on the recommended speeds and regulations I have referenced here, your opinion is definitely not shared by the company test pilots and certification authorities worldwide.

“The takeoff speed investigation should include a demonstration that controllability and maneuverability following engine failure at any time between lift-off and the 50-foot point are adequate for safe landing.”

...so, evidently, all certified single engine planes have demonstrably achieved what you think probably can't be done. Of course it requires the pilot “without undue skill” to act promptly and get the nose down but that is why we train and licence the pilots too.

So, to practice safely (before you assert that I'm wrong), try the following: Establish a safe hard deck for yourself, a few thousand feet up in the practice area. Do your HASEL check ('cause you're probably going to need it!) Slow the airplane at cruise power to Vx at exactly that altitude. Apply takeoff power, and climb from that altitude while maintaining Vx. At 50 to 100 feet, close the throttle. Now you're going to have to push the nose down fairly promptly to enter a glide, But, because you were actually expecting this, delay one second before you push to make it more realistic. Now establish the POH glide speed, and then, while referring to the altimeter, and leaving the throttle closed, momentarily arrest your descent at your hard deck altitude, just long enough to see the altimeter pointer pause there. If you can pause the altimeter there long enough to see that you did, you succeeded in a simulated flare and landing. If the plane just stalled, and kept on down through your hard deck, you crashed.
You may as well argue you can teach a pilot to land by establishing a glide and then giving them a target altitude to stall at. Your little exercise in aircraft control is seriously unrepresentative of an engine failure at 50', or any round-out for that matter, where you are controlling the plane primarily according to the ground references. If nothing else, you have totally overlooked ground effect. The certification basis for the safety of the take-off performance is to demonstrate an actual landing on an actual runway and does not include trying to accelerate from Vx up to the best glide speed that you seem to have fixated on.
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Old 22nd Feb 2021, 15:00
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I agree that some types have a best glide speed, and a Vx very close to each other, and that sounds happily safe. (Like having Vmca ans stall speed very close in a twin). I also know that pilots with practiced skill, be it unusual skill or not, can be really good at a precise flare from a "slower" power off speed - excellent! I know that ground effect can be favourable factor on a landing, but is not a dependable a way of preventing a hard landing. I also know that When you flare, particularly from a steep approach, (like power off), you're expending energy you've stored in airplane forward speed, to accelerate upward away from your descent path, enough to [hopefully] have your path be parallel to the surface. That acceleration means a very slight increase in G (acceleration), so the stall speed will have a very slight increase. So, stall speed is slightly increasing, while you're pulling to precisely time a flare, having that little bit of extra speed is nice then.

I also know that I have flown the certification flight testing for STC approval on several modified types (C150, C182, C185, and C208B) for 23.51, for this characteristic. I have found myself surprised that the slower power off speed required very much more application of skill to result in a suitable EFATO landing, and that was when I was expecting it. The opinion I hold is based upon my experience doing the testing. As a result of my testing, and the data gather, an STC was issued. In one case, the procedure to climb away slower than Vy had to be a special condition on the approval for lack of compliance (everyone agreed that compliance could not be shown for an EFATO at Vx).

My self designed exercise in power off descent and arrest at altitude was devised to remove the need to do this close to the surface, while still being able to demonstrate the effect. It has noting whatever to do with "landing" the plane, but rather managing the energy of the airplane, to save some for when you're going to need it at the flare. The lesson is your personal level of comfort in having, and being able to apply the reserve energy to momentarily arrest the descent at an altitude, as though you were landing there. When I train this, well briefed, nearly everyone I do this with falls through the hard deck with the stall warning blaring - which as not a nice way to be approaching the surface.

Unlike airplanes, helicopters have (by certification requirement) a height/velocity "avoid" curve presented in the flight manual. Because it is understood that from certain combinations of low altitude, and slow flight, a safe power off landing cannot be considered safe for the average pilot. I have also been trained to do autorotations from within that "avoid" range, it's very skill dependent. The same physics applies to airplanes as helicopters in this respect, though with different numbers. And, helicopters have an advantage that airplanes do not have for power off landings, as they can store energy both as forward airspeed, and as excess rotor RPM, where the plane can only store it as airspeed when that's spent, you're done.

What any pilot does, is up to them. I just would like pilots to consider a lesser known and understood factor which affects the safety of power off landings. I do not needlessly climb away at less than Vy. The three EFATO's I have had have all resulted in a no damage landing ahead. The flight testing I did for this nearly resulted in a damaged plane - when I was completely practiced and ready for it!

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