FullWings

Very difficult to say, due to the unpredictability of ground effect, wind gradient, drag characteristics of a 'dirty' airframe, engines that were producing significant thrust, etc. It's something that would require large gonads to experiment with in this situation... If it was *obvious* that a crash into houses/trees/petrol stations was going to take place, then what have you got to lose? Otherwise, a very difficult call. I wouldn't rely on a simulator to give a realistic answer in this scenario either.

It is well known that you can often escape an undershoot situation by using the technique described in the question above. What is slightly less well known is that the aircraft are generally "cleaned up" on recognition of a developing undershoot and the potential energy (height) converted into kinetic (speed), then bled off in the ground effect where the wing is more efficient. If you have gear and drag flap deployed on an airframe where configuration changes are slow and/or require a significant energy input, the act of speeding up to get into ground effect will probably bleed more energy than you'll save later and lead to an even shorter landing. It isn't called "drag flap" for nothing; in an overshoot situation, "pushing against the flaps" is a another well-known remedy.

The were no warnings (aural or visual) that anything untoward was happening. This is just one of the factors that made it a very difficult scenario to deal with. Does going into "Control Loop 17" mean the engine has become unresponsive? I don't have that level of knowledge but I believe it has something to do with surge/stall recovery, not a total failure. From a flight crew perspective, as it happened to one engine first, a warning would be noted but I suspect no action taken, as the 777 is perfectly happy coming in single engine F30, as the WAT limits are high in that config. By the time a warning came through for the other one, you'd be at the same place and time as the crew were on the accident flight.

It is easy to take the precise figures for BA38 and work out all sorts of things the guys might or might not have done. Change those starting conditions by just a small amount and the "best" course of action may change radically... It was a very dynamic situation and there was not enough information available at that instant to make calculated decisions - just instinctive ones. After all, here we are, eight months later, and no-one has definitively worked out what the optimum actions might have been...

snowfalcon2

No. You might want to look at my post #1736 to get confirmation on that point. This is a secondary issue, but not totally uninteresting, as many before me have shown .

As BOAC has stated (and others before), there is an altitude (or point in the approach) above which reducing drag pays off anyway and I'm referring to that phase - I'm not sure this was the case for BA038. The suggestion would admittedly be bad in those cases where the time for the action (say 5 sec) delays the engine restoration drill AND the engines would actually have responded in the last 5 sec before hitting the ground. In all other cases it would do no additional harm. Either the airplane crashes anyway or the engines save it before, or - in the fortunate case - the airplane would increase its chance to make the airfield.

Finding the root cause is paramount. However, if it's not found with certainty, there might be reason to consider the handling of low level dual engines-outs. Time will tell.

stickyb

Am I right in assuming that this detection method will only work when there is a distinct boundary condition - ie a layer of water or ice with a layer of fuel on top - as opposed to the situation where the tank just contains a mixed fluid?

CONF iture

You're correct Steve.
Just to make things more precise, graph in P6 says 8 seconds.


Technically and aerodynamically speaking, I don't see where sispanys ria is wrong ?
For every flying machine, the same rule apply and an optimal attitude will stretch your glide.

Would I have done better ?
Certainly not !
Probably a case for heart attack and best case scenario a compulsory underwear change before jumping in the slide ...

I think that crew has been very unlucky to be on that BA038 but in the same time has been very lucky to end it up the way it did.
But the worst for them was probably to have to go for that PR BA BS the very next day.
For the medals, I'm not sure they really care but would rather have all the data in their pocket which I doubt they have been given ...

Swedish Steve

Yes it detects the boundary. The transmitter is very low in the tank so it is usually immersed in fuel, and the beam goes down to the bottom surface and back.

pax2908

Reading again ... could someone please clarify the following (on Page 10 of the report): "approx 6500 to 7100 kg of fuel had leaked [] before the spar valves were manually closed". I thought these valves would be closed when the fire handles are pulled. But the quantity above seems quite large (to me!) ... so what does "manually" mean here?

BOAC

Posts #5-#12 and on will explain.

Jumbo Driver

It really would help if people read the AAIB reports before asking questions.

The answer to your question pax2908 is here on pages 5 and 6 of the AAIB Bulletin S1/2008, published back in February, if you would care to read it ...


JD

dxzh

FullWings and others well explain the practical uncertainties associated with the hypothesised alternative ways of handling the aircraft after the double rollback - particularly given the ever-developing critical position the crew found themselves in at literally the last minute and a slow, low, heavy aircraft in an initially stabilised but very draggy configuration.

The acid test in my simple world is that, if I were put back in the situation the crew found themselves in at that minute of that flight, then I would turn down each and every proffered "improvement" or “lesson” from any well-meaning speculator, who could (inevitably) only aver with less than 100% confidence that their alternative would work, in return for the certainty of the safe landing which the crew delivered on the day.

I think we should all be pretty humble and thankful that the crew did what they did with the poisoned chalice that they were given and that they saved the day. In my view the crew balanced the aircraft on the right side of the stall, they managed the little energy they had and got the right result, a safe landing - remarkable! This was a catastrophe which could have happened, but did not thanks to the crew.

VNAV PATH

sorry to be out of tune, but now starting to read all this thread !

somewhere written that the crew performed a managed approach .

what is it ?

thanks !

DC-ATE

dxzh -
>>> "I think we should all be pretty humble and thankful that the crew did what they did with the poisoned chalice that they were given and that they saved the day. In my view the crew balanced the aircraft on the right side of the stall, they managed the little energy they had and got the right result, a safe landing - remarkable! This was a catastrophe which could have happened, but did not thanks to the crew."


Ah, but how do we know that they might have made the runway had they left the flaps alone? Or might have gotten to the overrun. Granted things turned out alright, but they might've turned out better. We'll never know. And chances are the sim won't really prove anything. I just don't think their actions qualify them for any Flight Safety Award. Unless, that is, it can be proven that reducing the flaps at that critical point in flight was the right thing to do.

dxzh

DC-ATE, entirely fair comment on your part and I agree "We'll never now" - but I respect the crew nonetheless for what I do know which is that they got the plane down safely having been put into a potentially catastrophic situation by the double rollback - I would not begrudge them any praise for that achievement.

Carnage Matey!

I believe Boeings computer modelling has already proved that reducing the flaps was the right thing to do. Unless landing even shorter and ploughing through a busy road is considered a better outcome.

777fly

It has been suggested in this thread that crews are not trained to cope with a total loss of power at low altitude. I would propose that this is not so. Just consider the regular practice, in the simulator, of recovery from windshear or GPWS warning. In both cases, the aircraft is flown in such a way as to trade kinetic energy for potential energy, in a situation where engine power cannot meet the desired flight profile. In other words, trade speed for height. In these situations, kinetic energy is traded for height right back to the stick shaker, at which point attitude is adjusted to fly at intermittent stick shaker speed.
I would suggest that the crew of BA038 did, instinctively, follow exactly what they had been trained to do. Speed was bled back to the shaker speed and then an attitude adjustment was made to keep the aircraft flyable. Energy management.
There seems to be a perception that the stick shaker represents an entry into the stall regime, with loss of lift and control. This is totally wrong. The aircraft remains controllable and flyable at shaker speeds, as there is still a fair margin above the stall speed.

DC-ATE

I know about stick shakers having heard them numerous times in the sim; fortunately NEVER under actual conditions!

There is an obvious dissagreement in the handling of this flight with regard to flaps. I don't care what type airplane it is, however, if you raise the flaps, you've taken away lift and increased the stall speed: period. Any other action taken at that point other than lowering the nose will only aggravate the situation. As I stated earlier, I've had the flaps dumped on me and I know the feeling!

Being as I'm retired, I'll leave this now (unless called upon) to all you active types to sort out.

Again, we're ALL glad the outcome was as successful as it was. It probably speaks well for the aircraft also.

awblain

What options did the crew of BA038 have with respect to trading speed/kinetic energy for height/potential energy?

They had a finite reservoir of total energy, unless they could get power back. Worse, in fact, this energy reservoir was being depleted rapidly by drag: bleeding away into the turbulent air behind the flaps.

Going faster would increase drag further, taking away a larger fraction of their total energy per second. Going slower would reduce the loss rate, but too slow and what remains is forfeit in a stall.

The results of the manufacturer's detailed modeling of the precise circumstances: go for a bit less lift and quite a lot less drag, and squeeze the remaining energy out for as long as possible. The crew's intuition seems to have lead them to the same (right?) answer. A remaining question - does the computer modeling take into account the details of ground effect, surface topology and gusty wind in the final seconds?

777fly

Sorry DC-ATE, but I disagree. Retracting flap from 30 to 25 on a 777 has virtually no effect on lift, changes the stall speed by a negligible amount, but considerably reduces drag. In the energy management situation I recently described, it is a winner.

DC-ATE

OK 777fly, I'll leave it to you to keep these things in the air. Best of luck to you and your fellow pilots. Just glad I'm out of it.

snanceki

@777Fly.

I do not question your response to DC-ATE. or agree with his post. but simply ask...

What is the purpose of the 30 position IF it adds "negligible" lift yet adds considerable drag.

Surely the "negligible" must be closer to "significant" i.e. worth having or otherwise what is the point of such a setting?

I do not wish to rekindle the discussion re whether the crew should or should not have reduced the flap setting (I'm not interested and do not believe that at this point it has any relevance) but just question the premise against which the discussion is based, namely that 25 to 30 is "purely drag".

I am not a pilot. nor an aerodynamic specialist, but as an engineer I find it surprising that a function/position has been provided that increases drag but not lift...unless of course its purpose is as a brake, which may be the case.

So another way. What is the thinking/purpose in selecting 30 vs 25 under normal circumstances other than procedure calsl for it.

Please enlighten us.

NigelOnDraft

snancekl
Effectively the case. On the 757, Vref F25 was only a couple of knots above that of F30 - however, it gave you much mroe drag to keep the power "up" on Final Approach, enabling better speed control / engine response.

The airlines have now seen this and are getting 777 pilots to do F25 landings, and us Airbus guys to do F3 (Flap 3 rather than Flap Full). This keeps the Final Approach power low hence saves (a little) fuel. Depending on type the Approach and speed and Landing Distance increase by a bit, but the main effect for the crew on a steep glideslope / tailwind is dififculty having anything other than idle, against an SOP requirement of "Approach Power".

It makes the selection of F25 fairly instinctive, when day in / day out you are used to seeing a lower power setting for a F25 approach than a F30... someone takes the power away, lets go for the approach that needs less power

As has been pointed out elsewhere, most airliners on a go-around call for an immediate reduction of flap setting by one or even 2 stages - yet no increase in datum speed. Again, reason is pronounced reduction in drag (increased climb performance) with little reduction in lift.

NoD