BA038 update
I may have been a little premature in my earlier diary in casting aspersions on the automation while lauding the flight crew's ability to get this bird down in one piece.
According to the most recent update from the AAIB, the automation would appear to have been given a clean bill of health and isn't thought to have had any direct or indirect involvement in causing the accident. Far from it. Indeed it would appear that it was the automation and not any disclosed or reported intervention by the flight crew, that brought BA038 to rest via a full stall onto the only piece of forgiving real estate within miles of the airport on that fateful day.
The airspeed reduced as the autopilot attempted to
maintain the ILS glide slope and by 200 ft the airspeed
had reduced to about 108 kt. The autopilot disconnected
at approximately 175 ft, the aircraft descended rapidly
and its landing gear made contact with the ground some
1,000 ft short of the paved runway surface just inside the
airfield boundary fence.
I expect the investigation will now focus on the one remaining element that could logically have caused this accident - an interruption in fuel supply, with fuel 'waxing' (jelling) now topping the speculation leader board.
--
GW Bush, leading contender for worst President ever.
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References -
the gremlins have struck again.
Same aircraft type and engine combination (B-777 200ER/RR Trent 800) this time affecting an American Airlines flight into LA which was able to land safely. Hopefully, the investigation of this incident may shed some light on the fate of BA038.
--GW Bush, leading contender for worst President ever.
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)Icing could have caused loss of control or jamming of an elevator or aileron actuator. Gelling does sound more likely, though.
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)such as you suggest could affect the operation of the engines, the under performance of which we already know is the reason the aircraft crashed, though what specifically caused them to under perform remains unknown.
Are you pulling my leg?
Modern transport aircraft are well equipped to deal with atmospheric icing and water contamination in the fuel supply which may give rise to ice within the fuel. But not with freezing or 'jelling' of the fuel itself. The only way to combat this is to fly at altitudes that allow a safe margin between the outside air temperature and the freezing point of the fuel. While the recorded temperatures appear to indicate this safe margin was not broached on flight BA038, there is evidence that the aircraft flew higher and for a longer period through a region of significantly colder than normal temperatures compared to most aircraft on similar routings that day.
Curiouser and curiouser.
--GW Bush, leading contender for worst President ever.
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| parent )I was not referring to airframe icing, which is, as you correctly point out, an entirely different animal. Rather, I was referring to icing of control cables within the fuselage of the aircraft. Happened to my friend the pilot once: he had to land without elevators.
This does seem to be a different case. Gelling of the fuel does seem a plausible explanation, especially if one eliminates ILS software failure as a cause.
{Edited to include a link.}
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| parent )if not for the fact the 777 doesn't have control cables or any direct mechanical links between cockpit controls and the control surfaces, the control system is entirely fly by wire. Control surfaces are moved by electrically controlled hydraulic actuators in response to commands from a digital hub that processes control manipulations by the human crew and/or instructions from the navigational computers. I guess it's still theoretically possible that a 777 could suffer loss of control authority due to ice accumulation affecting the actuators, though this is highly unlikely given the design priority of avoiding failures known to have affected earlier Boeing aircraft like the 767 and the certification process requirements for an FBW aircraft.
Not that icing of any kind affecting the controls nor software failure appears to have played any part in this particular accident.
Fuel jelling sits atop the speculation leader board because practically everything else has been ruled out, conditions on the flight were favorable to its formation and it is as difficult to rule it out as it is to rule it in. Jet engines are at heart rather simple machines, starve them of fuel or air and they quit working, otherwise they tend to keep right on going unless some mechanical failure causes them to fly apart.
--GW Bush, leading contender for worst President ever.
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| parent )I'm going with the fuel theory as well. For efficiency purposes, commercial aircraft carefully consider just how many kilos of fuel to carry on any given flight. Just guessing here, but something tells me, based on the fact both engines lost power simultaneously, that the fuel pumps were sucking up the last dregs of fuel in the tanks and were fouled somehow. The engines would be at a low RPM on final, flaps full. Aircraft descends off its glide path, pilots bring engines up to full rich and the engines fail completely. What else but dirty fuel could produce such an outcome?
I will say this: the flight crew behaved heroically. Everything by the book, and a little more.
I only play one computer game: Flight Simulator. My preferred scenario is a landing on 27 Left O'Hare, flying a Learjet in driving rain and high winds. I only make the landing about 1 in three approaches, usually aborting within sight of the paint, pushing the levers forward, depending on regaining airspeed. I can only imagine what that flight crew must have felt like when they didn't hear the engines roar to life.
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| parent )a double engine failure (or as in this case, near simultaneous unresponsive engines) fuel exhaustion or starvation would be the most obvious conclusion and thus the 1st thing the AAIB would look at. They seem to have satisfied themselves in their report that there was "adequate fuel remaining" on the aircraft (some 10,500kg = 23,000lbs or about 3,450 US gals) which would eliminate fuel exhaustion.
Fuel starvation remains a possible cause and alongside the recorded performance of the engines which failed to deliver the requested thrust, there is some residual evidence of a restricted fuel supply event,
though there appears to be no evidence that ties this damage to the accident ie. damage to the pumps may have conceivably pre-dated the accident.
AAIB reports to-date have also assessed that the engine controls/hardware performed normally and as expected, so the only remaining conclusion would be that some restriction in the fuel supply caused by an as yet unknown and since disappeared contaminant led to the evident fuel starvation.
Curiouser and curiouser.
If you want to have some fun with your simulator have a go at some non-precision approaches, after all once you've shot one ILS you've practically shot them all. One of the more challenging approaches around would be the approach into Aspen, ASE. It's a circling approach not straight in, meaning that once you catch sight of the runway at the approach minimums you are too high to descend straight in to a landing on the runway and have to circle the airport in order to position yourself on a base leg before descending any further. Set the weather to just above approach minimums, say a 2,600' cloud base with 3 and a half mile visibility and give it a go. Hope you manage better than this crew did. Here's a great video of a night approach into Aspen using EVS, select Terrain Awareness Aspen. This was a specially authorized test flight, night approaches into Aspen are prohibited.
--GW Bush, leading contender for worst President ever.
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| parent )but I think they'd have had a Low Fuel annunciator screaming at them for a while by the time of the crash, and declared an emergency in response.
I agree...it must have been a terrible feeling to push those throttles and hear no response from that big bus strapped to their waists. For folks transitioning from props especially, it's often initially disconcerting to apply throttle to a jet and feel that delay before the added power translates to lift. But to hear no response at all? Pucker time.
--Excess on occasion is exhilarating. It prevents moderation from acquiring the deadening effect of a habit. - W. Somerset Maugham
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| parent )the crew had planned to arrive at Heathrow with 6,900kg of fuel remaining and the actual total was 10,500kg, which would tend to eliminate fuel exhaustion, though not fuel starvation due to some as yet indeterminate cause.
The realization by the crew that they lacked sufficient thrust would have been dramatic, but not as dramatic as what came immediately next. It's also more of a case that the throttles came up but then went back to where they had been rather than that they pushed up the throttles and got nothing.
As the AAIB report makes clear, BA038 was established on the approach and in the last 1/3 of the final descent to the runway before the problem surfaced.
the report then goes on to confirm that it isn't until 720' that the thrust of the right engine reduced below that requested by the autothrottles, followed some 7 seconds later by the left engine.
They don't quote the aircraft's speed or thrust at this point, but on a normal approach one would expect the aircraft to be within a few knots of its target approach speed with the autothrottles making only minor inputs to correct the airspeed.
Perhaps there is more to be gained from understanding what the report omits saying rather than what it does say. The report states the aircraft was established on the approach but it doesn't say the aircraft was established on a stabilized approach, defined as within +20 kts of final approach speed with a power setting appropriate for the configuration and not below the minimum required for the approach by the aircraft operating manual. This leaves open the possibility that the aircraft was a little fast, that the autothrottles where way back though above idle and that the aircraft was continuing to decelerate toward its target airspeed as it entered the final 1/3 of the approach. As the aircraft reached the required speed the autothrottles would begin to increase thrust in anticipation of stabilizing the airspeed, but for some unknown reason the thrust on both engines apparently returned to the previous low thrust setting and this resulted in a rapid bleed off of airspeed. From close to normal target approach speed of between 135-145kts at 720' to just above stall at 108kts by 200', a loss of 28-37kts in just 500'. By comparison the normal stabilised approach profile assumes the aircraft will bleed off 30kts between the start of the final descent at 2400' and the requirement to be stabilized at 1,000' in bad weather or 500' in good. The rapid bleed off in airspeed, 3 to 4 times the normal rate, is what would have commanded their immediate attention, that and the rapidly increasing deck angle as the autopilot attempted to compensate for the loss of lift associated with the loss of airspeed by increasing pitch to maintain the descent profile.
--GW Bush, leading contender for worst President ever.
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| parent )so I'll defer to your judgement. I'm not a pilot myself, but I did experience something similar back in my days as a broadcast engineer.
We had had a major ice storm in the Northeast, which took out utility power for a week. The station I worked for at the time was running its transmitter off a fuel oil turbine, and one night, the transmitter kept failing every five minutes or so. It turned out that the fuel lines to the turbine had gelled up, and were allowing just enough flow to run the generator at a standby level. Put a load on it, though (and a television transmitter is a honking big load) and the whole thing shut down due to fuel starvation.
Going back and reading the accounts of BAO83, it dies sound like that's what happened. It's certainly more plausible than control icing in a fly-by-wire plane.
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| parent )it's also quite a common problem with diesel fueled engines but if proven to be a significant factor in this case then it would be the 1st time as far as I am aware, that fuel 'waxing' were implicated in an aviation accident. Aviation fuels have a much lower freeze point than fuel oil or diesel. Jet A1, the specification of fuel uploaded by BA038, has a minimum temperature specification of -47C and according to the AAIB report the lowest recorded fuel temperature on flight BA038 was -34C, while fuel samples collected from the accident aircraft tested to an actual freeze point of -57C. Normal procedure is to ensure that the fuel temperature does not decrease to less than 3C above the minimum specification temperature which in this case would be -44C and it would appear from recorded data that the fuel in flight BA038 never got lower than 10 degrees warmer than this limitation.
If fuel 'waxing' is ultimately implicated in the accident then I guess the rules will need to be re-written, or perhaps the fuel temperature sensing arrangement in the 777 will prove to be inadequate, lacking sufficient fidelity? The 777 has only one fuel temperature sensor, located in the left wing and one assumes the engineers placed the sensor where they expected fuel temperatures to be lowest.
--GW Bush, leading contender for worst President ever.
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| parent )last sentence-don't be too sure. The engineers may have placed it there because it was the only place it would fit, because they felt like it, etc. Perhaps this should go in BlaiseP's thread but engineers ain't all that creative when it comes to stuff like that.
--I had discovered a great secret. That everyone loves themselves more than they love anybody else. And if I wanted them to love me, I better be like THEM!... Ken Nordine
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| parent )the engineer who decided the best place to locate the sensor was overridden by the engineer who had to determine how to get power to it and service it, or by the one who determined the most logical or easiest place to put it in terms of the production sequence, or by the one that was looking to trim cost? Wouldn't be the 1st time I'm sure.
--GW Bush, leading contender for worst President ever.
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| parent )Thanks for the update.
--The ultimate result of shielding man from the effects of folly is to people the world with fools. -Herbert Spencer
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| parent )nt
--Of course not!
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| parent )of something good.
--Fence post turtles -- They don't get up there by themselves, some moron had to put 'em there.
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| parent )