misd-agin

Joshilini - the report says the Captain retracted the flaps in an attempt to reduce drag.

The stall speed reduction from flaps 30 to flaps 25 is 2 kts. That requires a higher AOA to achieve the same amount of lift. I have no idea, and I doubt very many, if any, non Boeing test pilots know if reducing the flaps from 30 to 25 is a net reduction in total drag. I don't know the answer. I'll await the results of the investigation. However, based on the resulting AOA increase I tend to doubt that total drag was reduced.

If you have time you can test this in the sim. Set up a steady flight condition, fly Vref -20, and retract the flaps from 30 to 25. Fuel flow goes up, you're fighting more drag. Fuel flow goes down, total drag is less. I'd recommend turning level flight to increase the power, thereby making it easier to see any differences in power required.

S.F.L.Y

misd-agin, your statement is very correct provided the aircraft flies the same speed. In this case the AOA didn't only increase to compensate the flap reduction, but also (and mainly) because the speed dropped seriously low. Flying just before the stall speed would involve a high fuel flow increase, meaning significant increase in drag. Letting the speed drop so low while aiming too far for touch down is definitely ending in shortening the path with high Vz impact as there's no other way to get back some of the wasted energy to maintain some lift on the wings.

misd-agin

S.F.L.Y - I've been told L/D is slightly faster than Vref. Slowing below L/D decreases your glide distance. Doing it too early, with not enough altitude to push over and regain L/D, is only going to increase your sink rate and resulting impact.

Joetom

Just appears to me, crew had little time, they made some decisions, aircraft touched down with suitable pitch/roll and speeds and resulted in a great outcome on that day.

Touch down shorter could have been more of a problem with a drain of some sort I think they mentioned.

Touch down later and ramping up on runway from mud may have been more of a problem.

Hindsight is great after the events.

I still have my hat off to all the crew, well done.

misd-agin

Joetom - I agree, they had very little time and hindsight is 20/20. However, that doesn't mean we shouldn't investigate, and understand, what was helpful and successful and what wasn't. That is the nature of our business.

WojtekSz

@S.F.L.Y:

lets get the picture right:
we are flying B777 standard approach, at 500ft the speed is 135kias as needed, AP is engaged, gear down, flaps 30. Speed is getting too low so we increase the power, wait 4 sec for reaction, there is none so reduce throttles and reapply full throttles again, wait 4 sec for reaction. The a/c is now about half way down at 240ft, speed is 115kias. Pitch grew to +8deg. All this took 26 sec.

Due to lower speed the time we will stay in the air would be much shorter than this 26 sec (actually it was 17 sec). There are some buildings before we are over the threshold.

Just see how the flaps 30 are viewed from a side! Gear down+flaps form a huge airbrake which takes some 30..50% engines power to keep the speed stable!.
The drag/lift difference between flaps 30 and flaps 25 is like between landing and take-off because flaps 25 may be used for take-off.

afaik AP was doing what it was supposed to do - keeping the a/c flyin to the destination. The speed was too low, no reaction to AT so the attitude had to go up. With no engines reaction to manual full throttle PF had to react whatever way was available at such limited time/circumstances.

so there we are: at 240ft, flaps 30, 115kias with two choices: (1) fly at the a/c as is or (2) do something to reduce drag

if you know the drag difference between flaps 30+wing at appropriate attitude and flaps20+ appropriate attitude - than there is no brainer

WojtekSz

@ misd-agin + bearfoil

absolutely correct at speeds comfortably above Vs.
but when we are just a few knots above Vs, with the a/c slowing down - anything that keep the plain flying at above Vs has absolute priority.

Me Myself

Hi evryone

I haven't followed the thread for a very long time and it's grown to big to read it all.
Someone mentioned to me the Captain and the F/O had been given the sack by BA.
I have somehow a hard time believing it. Could anyone in the know confirm the fate of these 3 pilots ?
Thanks

chrisN

See the captain's own post no. 2657 on page 133.

From his own website, found using the hint in post 2657: it appears that he left British Airways (implying by his own wish) to pursue a speaking role talking of his experience.


Chris N.

S.F.L.Y

Wrong, the AP was trying to land the aircraft hundreds of meters away from the threshold as this is where the ILS leads. Trying to maintain this path at the expense of speed wasted energy and lead to high Vz.

We know the aircraft had enough total energy to reach its actual touchdown point and we know a lot of kinetic energy has been wasted by the AP... instead of being used to reduce the impact Vz.

Why do we need to have two pilots in the cockpit if none is able to monitor and control the airspeed through primary flight controls (which doesn't include flaps)?

S.F.L.Y

What kind of low speed protection can be designed to maintain an ILS without thrust?
Rocket boosters maybe?

deeceethree

On the B777, as long as the autothrottle is armed (but not necessarily being used), it should automatically activate stall protection if an ILS is being flown using the autopilot or flightdirector in G/S (glideslope) mode, but only up until 100 ft radio altitude on the approach. Thrust should be increased to maintain minimum manoevring speed (approximately the top of the amber band) or the speed set in the mode control panel speed window, whichever is greater. The EICAS message AIRSPEED LOW will be displayed if this occurs.

Obviously, in the BA038 case there was no thrust available to increase the speed.

maynardGkeynes

Isn't there a fuel cutoff switch in the B777 cockpit? Is it clear beyond any doubt that the crew didn't hit the switch by mistake? Would such an event be something that the "black box" would definitely have recorded? With all the exotic explanations being offered, isn't it just possible that the investigators have overlooked the obvious? Just asking....

deeceethree

I expect that, with no thrust available, the stick shakers would operate and the pilot would have to (be expected to?) override or disconnect the autopilot to avoid stalling. Initially at least, if left to it's own devices, I think the autoplilot would still attempt to follow the glidepath. Would it attempt to follow the glidepath until it fell out of the sky? I can't find a definite answer at the moment, sorry.

The crew did not have a switch-pigs whilst airborne - the recorded data would show that. Have you not read any of the AAIB reports?

maynardGkeynes

The report talks about "uncommanded" spars activation. I was referring to a "commanded" but accidental activation of spars. But looking at the report again, they say that the spars remained opened at all times. So that's pretty definitive. However, the report does not actually state that a commanded spars activation could not go unrecorded -- it says that an uncommanded one could not go unrecorded -- but I guess they felt it was obvious that either would be recorded. Thanks for the reply.

WojtekSz

@S.F.L.Y:
oups - i had an impression that the ILS was much more advanced and would actually lead the plane to land EXACTLY at the beginning of the runway - but who knows - maybe i was wrong
or maybe you have missed something ? Maybe it is just the localizer (direction guidance) that is located at the other end of the runway?

you seem to be pretty confident about this total energy but actually lets think: a/c was landing following the ILS slope, the speed and height were just right. Under normal conditions before final touchdown the engines would be giving some 50% thrust fo another 35..40 secs and this would make the a/c land exactly at the threshold as defined by ILS g/s.
So if the engines stopped some 40 secs too early this creates significant energy deficit. Exact amount of the missing energy can be calculated if needed. Just let me know if this qualitative description is not enough.
This is a little like driving your car into the garage: one do not seem to need much power to do so. But try to push your car into the garage without engine running...

could you pls remind us who did pushed the thrust levers to full? Didn't the pilots try to control the airspeed with the engines first, and only when has proved unsuccessful they have turned to the whatever else existing means were available to them: reduced flaps to reduce drag and lowered the nose to stay above Vs

suninmyeyes

Suitcaseman,

In reply to your earlier question. If available thrust reduces, the 777 autopilot will fly the ILS glideslope until the speed reduces to just above the stall. It will then ignore the glideslope, lower the nose and descend just above stall speed. If the 038 had hit the ground in this configuration everyone would not have walked away. That statement is based on having seen it a few times in the simulator. Full up elevator, (unheard of in a 777 landing) had been applied at the appropriate time just before impact to cushion it so that many of the occupants thought on touchdown that it was just a hard landing.

The speed protection logic is the same as if you have an engine failure at high altitude in the B777 but maintain alt hold. The speed comes back to just above the stall and then the aircraft descends at that speed and ignores the engine out target speed.

Mmmayday38

MaynardGKeynes wrote:
"Isn't there a fuel cutoff switch in the B777 cockpit?
Is it clear beyond any doubt that the crew didn't hit the switch by mistake?
Would such an event be something that the "black box" would definitely have recorded?
With all the exotic explanations being offered, isn't it just possible that the investigators have overlooked the obvious? Just asking...."


I'm not sure if this was a question to bait me into answering...but it worked!

Simply;
Yes, there are two fuel cutoff switches in the F/D.
Yes, it is clear the crew didn't 'hit' the switch by mistake... (I did check at the time!)
Yes, it would have done.
NO, the investigators (AAIB, NTSB, Boeing, BA or the Fire Dept's pictures) couldn't have overlooked it!

Thanks for asking though.

I was about to reply to 'Suitcaseman' about his question relating to 'stall protection' on an approach; but I see that it has been answered now.

Me Myself

thanks a lot

M.Mouse

Retracting the flaps from 30 to 20, descending until approx 200' then flying level in ground effect and extending the flaps as the speed decays worked in the simulator enabling touchdown on the threshold of the runway.

What all that ignores is that in the simulator the event was expected, reaction to the power loss was immediate and the plan had already been formulated. The BA38 crew did not have that luxury and so really the exercise was a little academic.

It is by no means meant to imply that the crew should have done better.