Possible Causes of the Boeing 777 Crash Landing at Heathrow?

[Art]

A Boeing 777 crashed yesterday at Heathrow apparently due to engine failure

Engines blamed for BA crash-landing
By Paul Majendie and Jeremy Lovell Reuters - Saturday, January 19 12:13 amLONDON (Reuters) - Investigators said on Friday that the engines of a British Airways Boeing 777 failed to respond to demands for more thrust shortly before it crash-landed at Heathrow Airport on Thursday.

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Thirteen people were injured when BA flight 83 from Beijing came down well short of the southern runway and the 136 passengers were evacuated down the aircraft's emergency chutes as fire crews doused the plane with foam.

Giving details of its initial investigation, the Air Accidents Investigations Branch (AAIB) said: "At approximately 600 ft and two miles from touch down, the Autothrottle demanded an increase in thrust from the two engines but the engines did not respond."

"Following further demands for increased thrust from the Autothrottle, and subsequently the flight crew moving the throttle levers, the engines similarly failed to respond."

http://uk.reuters.com/article/domesticNews/idUKHO86894720080119?pageNumber=1&virtualBrandChannel=0

In the event of catastrophic engine failure wouldn't it be normal for Boeing to issue instructions for safety checks or even ground other 777s until the cause was found?

Boeings lack of reaction and the fact there was no fire makes me wonder is it possible the plane just ran out of fuel??

 

[Evo]

A Boeing 777 crashed yesterday at Heathrow apparently due to engine failure
In the event of catastrophic engine failure wouldn't it be normal for Boeing to issue instructions for safety checks or even ground other 777s until the cause was found?

Boeings lack of reaction and the fact there was no fire makes me wonder is it possible the plane just ran out of fuel??

We probably won't know for awhile.

 

[Argentum Vulpes]

A Boeing 777 crashed yesterday at Heathrow apparently due to engine failure
In the event of catastrophic engine failure wouldn't it be normal for Boeing to issue instructions for safety checks or even ground other 777s until the cause was found?

Boeings lack of reaction and the fact there was no fire makes me wonder is it possible the plane just ran out of fuel??

It might also be a problem related to just RR engines and not anything with the other subsystems of the airframe. The trip 7 also uses P&W and GE engines. If it was found to be a problem with just the RR engines only the models using the RR engines would have to be grounded. However since it was only with one plane and no life was lost so far I believe it is up to the individual carriers to decide if they want to inspect/ground there 777s.

 

[Cyrus]

A Boeing 777 crashed yesterday at Heathrow apparently due to engine failure
In the event of catastrophic engine failure wouldn't it be normal for Boeing to issue instructions for safety checks or even ground other 777s until the cause was found?

Boeings lack of reaction and the fact there was no fire makes me wonder is it possible the plane just ran out of fuel??

No. The airplane was no where near out of fuel (All flights have at least an hour reserve). It could have been fuel starvation, or a software error. The engines were running, they just didnt spool up. Thats not lack of fuel. This wasnt "catastrophic engine failure". It was an engine failure.

I would bet on a software error (777 is all fly by wire).

 

[Garth]

One report in our newspapers said they lost avionics as well.

Both engines and avionics?

It must have beeb a computer glitch, and yes Boeing ought to ground and check all the 777s until the cause is established.

Garth

 

[Andre]

No. The airplane was no where near out of fuel (All flights have at least an hour reserve). It could have been fuel starvation, or a software error. The engines were running, they just didnt spool up. Thats not lack of fuel. This wasnt "catastrophic engine failure". It was an engine failure.

I would bet on a software error (777 is all fly by wire).

I certainly hope that you are right. There is a tendency to have systems like that redundant. The F-16 for instance has 4 identical flight control computers, three of them operating directly, while the three signals are continuously compared. As soon as one signal is deviating, it is kicked out and the fourth system is included. What can go wrong?

Well, we lost an aircraft because the wiring of all the systems had the same routing and an electrical short cut damaged the wiring of all four systems.

So if two engines don't respond simulaneously, given the control system reduncancy the amount of probable causes is very limited and would not exclude fuel starvation for whatever reason.

 

[Garth]

One factor was that below 600 feet warning signals are suppressed to avoid distracting the pilots on landing.

As a consequence the pilots didn't know they had a problem until the co-pilot John Coward noticed they were losing speed.

Perhaps this is what they meant by "losing avionics".

I would have thought that when approaching a landing there were certain warning signals that you actually would want to hear, such as: "You've lost your engines!"

BTW, as a point of information, they had 10 tonnes of fuel left on landing.

Garth

 

[Cyrus]

One factor was that below 600 feet warning signals are suppressed to avoid distracting the pilots on landing.

I would have thought that when approaching a landing there were certain warning signals that you actually would want to hear, such as: "You've lost your engines!"

At 600 feet and at least 150KTS, a warning signal is a pointless distraction. You are too low, and there is no time to do anything about it.

What would 'your engines won't spool up' do in that situation? Absolutely nothing.

 

[wolram]

At 600 feet and at least 150KTS, a warning signal is a pointless distraction. You are too low, and there is no time to do anything about it.

What would 'your engines won't spool up' do in that situation? Absolutely nothing.

I guess the only alarm needed at that height is a stall warning or terrain warning.

How is the flying going Cyrus?

 

[Astronuc]

The Air Accidents Investigation Branch of the UK's Department for Transport is now investigating the incident. A team from the U.S. National Transportation Safety Board is also heading to London, accompanied by representatives from Boeing and the Federal Aviation Administration.

http://www.cnn.com/2008/WORLD/europe/01/18/boeing.causes/

Boeing is apparently providing technical assistance, but they probably won't know much until they check the flight recorders - black box.

It could be a software or hardware/component failure, and they'll look at human factors as well.


http://news.bbc.co.uk/2/hi/uk_news/england/london/7197506.stm

 

[Garth]

At 600 feet and at least 150KTS, a warning signal is a pointless distraction. You are too low, and there is no time to do anything about it.

What would 'your engines won't spool up' do in that situation? Absolutely nothing.

One thing that will be examined in the investigation will be whether the pilot could have reacted more quickly, which just might have bought more time to adjust the glide path.

A warning signal could well have been useful and not a pointless distraction.

As it was, the engines were throttled back for landing so the fact that they had failed was not noticed until the pilot saw the air speed was dropping. The controls began to vibrate which told him he was approaching a stall.

When he found he could not get any power from the engines he put the nose down to gain flying speed.

In doing so he lost valuable height which resulted in him landing short of the runway, fortuitously not too short. (I used to live about two miles down that glide path!)

Garth

 

[Art]

One factor was that below 600 feet warning signals are suppressed to avoid distracting the pilots on landing.

As a consequence the pilots didn't know they had a problem until the co-pilot John Coward noticed they were losing speed.

Perhaps this is what they meant by "losing avionics".

I would have thought that when approaching a landing there were certain warning signals that you actually would want to hear, such as: "You've lost your engines!"

BTW, as a point of information, they had 10 tonnes of fuel left on landing.

Garth

Watching the pilot being interviewed he said there was no power from the engines whatsoever when he landed. What could cause 2 engines to fail simultaneously other than a fuel problem?

 

[Astronuc]

Watching the pilot being interviewed he said there was no power from the engines whatsoever when he landed. What could cause 2 engines to fail simultaneously other than a fuel problem?

Loss of avionics such that the throttle didn't respond.

It almost seems like the cockpit controls (or the part that includes the throttle) were disabled! In that case, there is nothing the pilot can do. He might have been able to pull the nose up to gain lift at the expense of forward airspeed, or reduced flaps with an increase in pitch.

As far as the pilot goes, he doesn't have a lot of time to understand and act when the plane is at 180 m and 3200 m out. Presumably something would have indicated that the plane was below the glide plane.

At 150 kts ( 77 m/s) the pilot had 41 seconds to impact - not a lot of time to understand the problem and take effective corrective action.

 

[Garth]

Watching the pilot being interviewed he said there was no power from the engines whatsoever when he landed. What could cause 2 engines to fail simultaneously other than a fuel problem?

I agree with Astronuc; there were two independent fuel tanks and supply systems feeding the engines individually.

It would seem the height of bad luck to lose both simultaneously!

Garth

 

[Cyrus]

http://www.youtube.com/watch?v=yp1KwPgogHU&feature=related

Look out the window at 500 feet. Your engines quit at that point and you are up sh!t creek w/o a paddle.

 

[Astronuc]

I posted this additional information in the Air Crash thread in the Mechanical and Aerospace Engineering forum.

http://aviation-safety.net/database/record.php?id=20080117-0

http://www.aaib.dft.gov.uk/latest_news/accident__heathrow_17_january_2008___initial_report.cfm


Interestingly, there was a problem with the 777 in Australia.
http://www.airlinesafety.com/faq/777DataFailure.htm

On August 1, 2005, a Boeing 777-200, which had departed from Perth, received an EICAS (Engine Indication and Crew Alerting System) warning of low airspeed, as the plane was climbing through FL (flight level) 380. Simultaneously, the aircraft’s slip/skid indication moved full right, on the PFD (Primary Flight Display). The PFD speed tape also displayed contradictory information: that the plane was approaching both the high speed limit and the low speed (stall) limit. The aircraft, still connected to the autopilot, pitched up and climbed to approximately FL410 as the airspeed decreased from 270 kts to 158 kts. The stall warning devices also activated.

I wonder if this failure had any commonality with the BA038 problem.

Until the flight recorders are analyzed, it's too early to tell.

 

[Andre]

There is the possibilitity of engine icing but that requires quite a set of adverse conditions to be met.

 

[chroot]

At 600 feet and at least 150KTS, a warning signal is a pointless distraction. You are too low, and there is no time to do anything about it.

This is absolutely false. Instrument landing system decision altitudes are generally no more than 200 feet above ground level. Pilots routinely fly approaches down to decision altitude in zero-visibility conditions and conduct missed approaches from that altitude. Even at 600 feet above ground, with visual contact, the pilots would have had plenty of time to change their minds.

- Warren

 

[Cyrus]

Warren, the engine was not spooling up at 600 feet. What could he have possibly changed his mind about? Was he going to do a go-around with no power?

 

[chroot]

It almost seems like the cockpit controls (or the part that includes the throttle) were disabled! In that case, there is nothing the pilot can do. He might have been able to pull the nose up to gain lift at the expense of forward airspeed, or reduced flaps with an increase in pitch.

If the aircraft already has its flaps fully extended, and is losing airspeed to the point that it may stall, retracting the flaps will result in an immediate stall. The point of the flaps is to allow slow flight (or add drag in situations where it is desired). Pulling the nose up would also result in an immediate stall.

As far as the pilot goes, he doesn't have a lot of time to understand and act when the plane is at 180 m and 3200 m out. Presumably something would have indicated that the plane was below the glide plane.

Again, 600 feet actually gives the pilot plenty of time to make decisions, if the aircraft is operating normally.

- Warren

 

[chroot]

Warren, the engine was not spooling up at 600 feet. What could he have possibly changed his mind about? Was he going to do a go-around with no power?

If you have enough airspeed, the appropriate thing to do is to retract the flaps a bit, reduce your drag and land fast. In this case, the pilot apparently was near stall anyway (though I don't know how on Earth his first indication of a stall would be the controls getting mushy or vibrating -- a dozen other things indicate a stall before this), and retracting the flaps would have meant losing attitude control and crashing in a very bad way.

The pilot probably did everything right in this situation, though I don't know all the specifics. Planes are disposable, people are not -- he chose wisely.

- Warren

 

[Cyrus]

Absolutely. In an engine failure on takeoff or landing, you don't want to change course more than 60 degrees from the nose. So in his case, he really had no choice but to land straight. An airplane that big that low with no power would make my pants brown. I am sure the drag on that thing with no power will slow it down significantly. They usually don't idle until the threshold. Big airliners have 'shakers' on their controls that indicate the inception of stall to simulate the nautral shake in a cessna. I think he had the flight director on, which would normally maintain airspeed so it wouldn't be on his mind.

That plane is a total loss though

 

[Ivan Seeking]

Cyrus, I just wanted you to know that when I heard about a plane missing a runway, you came to mind immediately.

 

[Astronuc]

If the aircraft already has its flaps fully extended, and is losing airspeed to the point that it may stall, retracting the flaps will result in an immediate stall. The point of the flaps is to allow slow flight (or add drag in situations where it is desired). Pulling the nose up would also result in an immediate stall.

I'm aware that the point of flaps or greater pitch is to allow for slow flight (approaching landing speed).

I had in mind that the pilot would have to retract flaps a bit and put the nose down (if it was up) in order to gain speed to get to the runway (as was indicated a subsequent post). And then nose up or flaps down, whichever is quicker (and IIRC is the nose up is quicker) at the last second.

But as was subsequently indicated, the plane had insufficient velocity, and the pilot was attempting to increase thrust without success.

Again, 600 feet actually gives the pilot plenty of time to make decisions, if the aircraft is operating normally.

The pilot had about 41 seconds to understand the problem and act. That's not a lot of time.

And I think the point is that the plane was not functioning/operating normally.

 

[chroot]

I had in mind that the pilot would have to retract flaps a bit and put the nose down (if it was up) in order to gain speed to get to the runway (as was indicated a subsequent post).

Reducing drag by retracting flaps would be a wise decision if the aircraft had sufficient airspeed to prevent a stall, but apparently it did not. Flaps are critical in providing the lift necessary for slow flight. Putting the nose down would pretty much never be a wise decision, as that trades altitude for airspeed. The pilot didn't really want airspeed; he wanted altitude, but the engines could not deliver it.

Each aircraft has a flap/pitch combination that results in the largest glide ratio. If the pilot had had enough time and knew he was not going to get any more thrust, he would have set the aircraft up in that manner.

And then nose up or flaps down, whichever is quicker (and IIRC is the nose up is quicker) at the last second.

You don't need flaps to land, nor do you really need a flare. You can land fast with no flaps, and you can land flat and accept a much larger possibility of damaging the nose gear -- obviously an acceptable decision in this situation.

And I think the point is that the plane was not functioning/operating normally.

Right. Given that the pilot had no more thrust and was already near a stall, the only thing he could really do is put it down and hope.

- Warren

 

[Andre]

. Putting the nose down would pretty much never be a wise decision, as that trades altitude for airspeed. The pilot didn't really want airspeed; he wanted altitude, but the engines could not deliver it.

Sorry, Warren but no, absolutely not. You need a few knots overspeed to be able to flare the aircraft and kill the rate of decent just seconds before the touchdown. Ask any pilot why speed is life. They had no other option to put the nose down, pick up a few knots and be able to flare out just before though down. That part went very well.

 

[chroot]

Sorry, Warren but no, absolutely not. You need a few knots overspeed to be able to flare the aircraft and kill the rate of decent just seconds before the touchdown. Ask any pilot why speed is life. They had no other option to put the nose down, pick up a few knots and be able to flare out just before though down. That part went very well.

The flare is essential for the aircraft, not for the passengers. Again, you can land a plane flat if your goal is simply to preserve life -- who cares about the nosegear? I'm a pilot, by the way, and speed is not life; altitude is life.

- Warren

 

[Andre]

The flare is essential for the aircraft, not for the passengers. Again, you can land a plane flat if your goal is simply to preserve life -- who cares about the nosegear? I'm a pilot, by the way, and speed is not life; altitude is life.

- Warren

Hmm, if you loose your engines and if you know for sure that you're not going to make the runway, one thing you must certainly aim for, the ability to break the rate of decent before touch down, which is catastrophically invertionally proportionally to speed and (not available) thrust combined. Not really if you're pilotting light weights or gliders but most certainly, if there are some multiple tons under your pants.

 

[chroot]

Rate of descent is "catastrophically invertionally proportionally to speed?" Stop while you're ahead.

- Warren

 

[Andre]

Well if you're pilotting a glider or a light weight you'd be happy with a few knots above stall speed. You'd only need a few feet to convert altitude to speed. But when you'd have to multiply the weight/speed/thrust numbers a few digits, things are getting quite differently.

 

[chroot]

Andre, I'm sorry, but I don't think you have any idea what you're talking about. The ideal landing is very near stall speed in ALL aircraft, including big ones. You want to land as slow as possible to shorten your roll -- if the aircraft is operating properly. If you've lost your engines, you want to set the aircraft up in whatever configuration maximizes your glide ratio so you can actually obtain the runway. This configuration will result in a faster-than-normal landing in every airplane I'm familiar with. Futhermore, this glide configuration already produces the lowest possible rate of powerless descent, and that's how you want to land. Forget the flare, forget the nosegear, forget proper form and bonus points for imperceptible maingear touchdown. Just put it on the damn tarmac with everyone still alive.

The weight and thrust of the aircraft have nothing to do with these decisions. I really don't think I have any idea what point you're trying to make anymore.

- Warren

 

[Cyrus]

I don't know if its even possible to do a flaps up landing on an A/C that large. But as the saying goes, "Your altitude deterimines your attitude".

Andre, please don't fly any airplanes.

 

[Ivan Seeking]

I think Andre was a career fighter pilot or similar?

 

[Ivan Seeking]

Ah yes, here we go.

I'm a semi-retired fighter pilot and I published four articles about strategy and air power in a mean stream Dutch military journal.

https://www.physicsforums.com/showthread.php?p=1233209#post1233209

 

[russ_watters]

I don't know if its even possible to do a flaps up landing on an A/C that large. But as the saying goes, "Your altitude deterimines your attitude".

It is - it ain't pretty, but it is possible. You're just going too fast, it doesn't necessarily mean a hard landing.

United 232 (Soux City) came down without flaps and probably would have been fine if it hadn't caught a gust right before touchdown. Given the condition of the plane, though, it was miraculous they got that close to a safe landing.

edit:
Wow, never heard about this one: http://www.pages.drexel.edu/~st55/Research/DHL.pdf

An A300 landed safely at Baghdad airport after being hit by a SAM that severed and drained the hydraulic lines. The pilot was able to control the plane partly because a few months earlier at a seminar, he heard a talk about how they (almost) landed United 232!

It's a little unclear about the landing speed (either 225 or 180kts), but it sounds like the flaps were retracted, but slats were extended (in takeoff configuration, as it was hit on climbout).

 

[russ_watters]

I remember hearing once that to fighter pilots, energy is life - but they were talking about dogfighting, not landing.

Anyway, the fly-it-into-the-ground technique warren's describing seems to have been pretty much validated by the outcome of this crash. It destroyed everything hanging below the plane, but they made it to the airfield and no one died.

 

[chroot]

Well, I'm only a private pilot, still working on my IFR, with no air carrier or (gasp) dog figthing experience. All I can say is how I'd fly my own aircraft were it powerless. I'd set it up for maximum glide ratio all the way to the threshold. If I didn't make the threshold, there's no way I'd even consider a flare. I'd land it dead flat, do everything I could to keep the wingtips from hitting the ground, and let the destruction of the undercarriage slow me down. Warren 1, plane 0.

- Warren

 

[Andre]

Don't you think that a 15 tonnes fighter aircraft also has to obey simple basic aerodynamics on final approach? There might be a slim change that a semi retired fighter pilots knows what he is talking about after having done that ...oh... perhaps 3000 - 4000 times?

The 600 feet / 2 miles resemble a 3 degrees glidepath which is pretty standard nowadays, without engines a modern jet glides about a nautical mile losing 1000 feet. The difference is thrust. Thurst also helps in the flare, when the trust vector is pointed more upwards, the vertical component adds to the lift. A standard trick for a super soft landing is adding a bit of thrust a second or two before touchdown. However the aircraft owner is usually not amused by that because it wears down tyres pretty fast.

The point is though that without engines you need more speed to be able to break the rate of descent. And for a jumbo sized flying contraption that's not for the comfort of the passengers but has to do with the difference of dropping a mouse or an elephant from 20 feet. Mouse runs away Elephant is likely dead. Pure inertia.

So in this case, without engines and 'behind the power' curve, already losing a lot of speed there was no option than dropping the nose, pick up speed and concentrate on the flare, which they seemed to have done rather professionaly.

 

[Andre]

Just to explain in general:

without engines and 'behind the power curve'

This is a generic aircraft "power curve"

showing how the drag is speed related, at the high end drag is evident, at the low end, the induced drag is the mainly result of increasing pressure differential under and above the wing apart from some other effects like turbulent boundary layers. The solid drag curve also resembles the energy required to maintain that speed. So the approach speed is an trade off between these effects, somewhere around the minimum drag point, and you would try to avoid getting into the speed region where the induced drag becomes dominant, because slower speeds require more thrust. that's called "behind the power curve". In a slow decent things change hardly, the engines deliver not enough thrust to maintain level flight and you get the additional energy required to maintain speed by losing height, or actually potential energy. It's all a matter of energy.

So without engines, reducing speed gets you behind the power curve where the induced drags kills your energy pretty fast. Inevitable result is a stall and followed in this case by disaster.

You need to maintain the speed to remain in the lowest part of the drag curve. That's why speed is life. That's also true for a B777.

 

[pitot-tube]

Just to explain in general:



This is a generic aircraft "power curve"

showing how the drag is speed related, at the high end drag is evident, at the low end, the induced drag is the mainly result of increasing pressure differential under and above the wing apart from some other effects like turbulent boundary layers. The solid drag curve also resembles the energy required to maintain that speed. So the approach speed is an trade off between these effects, somewhere around the minimum drag point, and you would try to avoid getting into the speed region where the induced drag becomes dominant, because slower speeds require more thrust. that's called "behind the power curve". In a slow decent things change hardly, the engines deliver not enough thrust to maintain level flight and you get the additional energy required to maintain speed by losing height, or actually potential energy. It's all a matter of energy.

So without engines, reducing speed gets you behind the power curve where the induced drags kills your energy pretty fast. Inevitable result is a stall and followed in this case by disaster.

You need to maintain the speed to remain in the lowest part of the drag curve. That's why speed is life. That's also true for a B777.

Induced drag results from vortices that move forward in the direction of the aircraft.The aircraft slows down because of Newton's Law - every action has an equal and opposite reaction.Minimise the size and momentum of the forward moving vortices and you minimise the induced drag.If you hold a ruler vertically, with one end in some still water, and move it quickly you will see the vortex it sheds moves in the direction of motion of the ruler.

 

[pitot-tube]

So in this case, without engines and 'behind the power' curve, already losing a lot of speed there was no option than dropping the nose, pick up speed and concentrate on the flare, which they seemed to have done rather professionaly.

The best way to land a large aircraft such as a boeing 737 is to increase thrust a few seconds before touchdown - a compromise between getting the
aircraft to move slowly without allowing it to drop out of the sky.
Without engine power the pilot could dive to get the aircraft's speed up.But given the low altitude of the aircraft he couldn't have done a very significant dive.The aircraft landed at the perimeter of the airfield and this may mean that the pilot kept the aircraft landing as he normally would have done knowing it would be a close call -would the pilot have risked any tricky diving manoeuvre or adjustment of control surfaces over people's houses without engine power? Unlikely.

 

[Andre]

We not talking about more than a few degrees of course. Furtermore, if you don't change the pitch attitude of the aircraft, the slowing down will automatically increase angle of attack, meaning that the rate of descent increases, but in this situation a flare at slower speeds without engines will be rather futile.

 

[Art]

Would it have helped gain more airspeed and thus greater glide capability if the pilot had retracted the undercarriage or was it too late for that?

 

[Andre]

Aerodynamically yes but on the other end the landing gear absorbs a lot of impact energy while collapsing, reducing the damage to the rest as Warren observed.

Induced drag results from vortices that move forward in the direction of the aircraft.

I don't understand that. Yes there are wingtip vortices generated by the pressure differentials also known as 'wake turbulence' or even 'jetwash'.

Source NY Times

But that's more the result of the induced drag.

 

[rewebster]

great photo, Andre, reminds me:

has anyone here tried to win the million?


http://www.claymath.org/millennium/Navier-Stokes_Equations/

 

[Art]

Aerodynamically yes but on the other end the landing gear absorbs a lot of impact energy while collapsing, reducing the damage to the rest as Warren observed.

With the priority on actually clearing the airport perimeter fence wouldn't increasing glide ability be the number 1 priority? Plus for a landing on grass I'd have thought the SOP would be with undercarriage up to avoid the landing gear punching holes in the wings with the attendant risk of fire?? (at least that's what they always did in the old WW2 films :) )

 

[Andre]

The SOP's I know call standard for gear down emergency landings. Holes trough the wings would only happen at zero speed. At typical touch down speeds over 100 knots in soft soil undershoots would act as strong brakes until the gear collapses torn off to the back, sure there will be damage to the wing but that was inevitable anyway.

And it's is esential to have a few feet of breaking the sink speed, if that can be accomplished by the gear, that's a whole lot better than having the tail or the engines touch first, because those are going to deform also the same couple of feet with high risks of more structural damage than necesary.

 

[chroot]

This is all nonsense, Andre. You're arguing second- and third-order effects. This is a discussion about making a runway without any engines. Your mention of turbulent layers, wingtip vortices, induced drag, etc. is just unnecessary complication to make it sound like you've won the argument. I know this is how you usually conduct arguments, though: you throw jargon and complex language at people until they just give up and decide you must know more than they.

The bottom line: If you don't think you're going to make a runway, you don't give up altitude to gain speed so you can do a nice flare and protect the aircraft -- you keep it in best-glide configuration all the way into the ground, hoping all the while you might miss the super-highway, make the threshold, and keep your passengers alive.

- Warren

 

[Andre]

I guess we are repeating moves. You consider the flare unnecesary to keep the passengers alive, I think it may be correct for smaller aircraft but you underestimate the inertial effects of large aircraft

http://findarticles.com/p/articles/mi_qa3744/is_200505/ai_n13642230

One of the Class A mishaps involved a C-5 mission well into a long duty day, on a night VFR, idle power descent, tactical arrival into an airfield in the AOR. During the final turn, with throttles still in idle, the airspeed decayed to 10 knots below approach speed with a high sink rate. The crew was late in recognizing the aircraft's negative energy state. The pilots advanced the throttles 3-5 seconds prior to touchdown, but failed to arrest the sink rate. The aft fuselage contacted the runway causing extensive damage. This is the worst case scenario: slow, high sink rate, with throttles set to idle. If thrust is set to idle and maintained at idle, no energy is available immediately to recover from a low-speed condition or to initiate a go-around.

Point is failed to arrest the sink rate - extensive damage. And the sink rate in a glide is considerably more than a normal approach. This 777 was hardly damaged that way.

This guy agrees with me:

http://yarchive.net/space/launchers/horizontal_vs_vertical_landing.html

When landing an aircraft with the power off, the pilot must keep the airspeed high until he or she is ready to bring the flight path level with the ground and land.

For an F-16 normal approach speed is around 160 kots weight depending but in a flame out pattern we use 220-230 knots.

 

[chroot]

You don't understand -- you have two choices:

1) Slow the rate of descent by giving up altitude, and crash into the freeway outside the airport. Enormous property damage and many deaths result.

2) Fly the plane into the ground in best-glide configuration, missing the freeway and clearing the airport perimeter fence. The airplane will be a hull loss either way, but you might actually make the threshold and keep everyone alive.

-Warren