AAIB initial report out on BA B777 crash at LHR

[Pinkman]

Morpheme

People are going on about waxing and icing etc, because those are valid possibilities at the end of a sector especially one flown through the especially cold upper air conditions found on that day over the UK. Water and wax crystals sink in fuel, they are not homogenously distributed throughout the fuel. If they were to be an issue, it would be at the end of the sector. I agree its a very remote possibility but until the AAIB do their 30 day announcement, it remains as equally strong a contender as electronics, RFI, etc.

A4., no, it changes phase and resolubilises (sp?) as the temperature increases, but it takes temperature AND motion (jiggling around) to do it (I have done it in the test tube with both Jet and Diesel). Tubby is right - it does not revert instantaneously - there is a lag. Additionally, the smaller the volume of fuel, the quicker the initial icing would be.

P

[PJ2]

Bernd;

Re stalls and autothrust on the B777, the AOM provides the following, from 2.27.20:

Pitch Envelope Protection

The pitch envelope protection functions include:
• stall protection
• overspeed protection.

Stall Protection

Stall protection reduces the likelihood of inadvertently exceeding the stall angle of attack by providing
enhanced crew awareness of the approach to a stall or to a stalled condition.
Stall protection limits the speed to which the airplane can be trimmed. At approximately the minimum
maneuvering speed, stall protection limits the trim reference speed so that trim is inhibited in the nose
up direction. The pilot must apply continuous aft column force to maintain airspeed below the
minimum maneuvering speed. Use of the alternate pitch trim levers does not reduce the column
forces. When flying near stall speed, the column force increases to a higher level than would occur
for an equivalent out–of–trim condition above the minimum maneuvering speed.
The autothrottle can support stall protection if armed and not activated. If speed decreases to near
stick shaker activation, the autothrottle automatically activates in the appropriate mode (SPD or THR
REF) and advances thrust to maintain minimum maneuvering 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 is displayed.

Note:

When the pitch mode is FLCH or TOGA, or the airplane is below 400 feet above the airport
on takeoff, or below 100 feet radio altitude on approach, the autothrottle will not automatically
activate.

Note:

During a descent in VNAV SPD, the autothrottle may activate in HOLD mode and will not
support stall protection.

[Morpheme]

Well sorry if I sound dismissive (which I am) but even several hours in very low temps won't send 30-odd tons of fuel below -47degC.

As well the obvious question - why didn't all the Far East-originating westbound traffic fall out of the sky together?

[PPRuNe Towers]

Believe it or not

PPRuNe is writing to the Salvation Army to thank them for being on site hour after hour. They arrived with a catering van to make sure the all those involved in the investigation and recovery were fed and watered.

Rob

[Duck Rogers]

PPRuNe is writing to the Salvation Army to thank them for being on site hour after hour. They arrived with a catering van to make sure the all those involved in the investigation and recovery were fed and watered.

Rob

Soup sir? BIG ISSUE!!

Seriously though. They might be a bunch of God bothering biddies but well done.

[Sunfish]

Can people please forget about water in the fuel, waxing etc.? It's unlikely to be valid, otherwise jets would be dropping out of the sky daily all over the world.

For a start, Beijing is holding the Olympics shortly and they have thoroughly renovated everything aviational. As for waxing, the cloud point (at which wax freezes out of the fuel) for Jet fuel is very low and its tested when the batch is approved.

As for water, (as a former terminal engineer before joining an airline), I can tell you that oil companies are paranoid about water in jet fuel storage tanks. Furthermore, the fuel will have traveled through at least THREE filter/coalescer units (terminal, receiving station and final loader) which remove dirt and water before it is loaded into the aircraft tanks that should leave it clear and bright. So absent massive water contamination, that would by now have affected dozens of aircraft, in all probability this is a non-issue.

[Hand Solo]

My old Airbus is prone to ice on the exterior of the Outer fuel tanks.........There is no indication of fuel temperature in the cockpit.Cold soaked fuel takes a long time to warm-certainly more than the 30 minutes a 777 would take to get from top of descent to the ground

My old 744 is prone to ice on the fuel tanks too, but we have fuel temperature indications in the cockpit and the 30 mins it takes us to get from top of descent to ground is more than enough to significantly warm fuel above -40C. Once again, ice on the exterior bears no relation to waxing in the fuel. Ice will form as long as the fuel temp is below 0C. Wax won't form in the fuel until it's much much colder than that.

Edited to add that the freeze point is the temperature at which was starts to form, not the temperature at which it freezes, so the fuel in question would need to be close to -47C to support waxing. There's no way on earth the aircraft landed with fuel anything close to that temperature.

[chksix]

Also, there would have been an alert about fuel filter bypass if there had been an issue with fuelclogging.

[pax2908]

Are there previous instances (lets say on this A/C type+engine) of _one_ engine failing or being unexpectedly slow to respond during the approach?

[Contacttower]

It is clear from the report that the engines did NOT fail - they just did not respond to autothrottle / thrust lever commands when the thrust was supposed to come up at 600ft.

There does seem to be a lot of confusion over this, the AAIB report does seem rather at odds with what John Coward apparently told Sky News:

"The adrenaline kicked in when I realised I had to land the plane with absolutely no power at all. There are drills for a power failure at 30,000ft, when you have time to reset and restart engines, but there are no drills for this. As I approached the runway, I thought that this was going to be a catastrophic crash."

[looseobject]

Dual engine flameout on A330

Extracts from an AD issued after an A330 (QR i think) experienced a dual engine flameout.

Several A330 aircraft equipped with General Electric (GE) CF6-80E1 engines
experienced an engine flame out during descent, 2 to 3 seconds after engine
acceleration upon aircraft altitude capture, under inclement weather conditions. In all
cases, the engines restarted and then operated normally.
Analysis has shown that at high altitude an accretion of the conventional ice or ice
crystals in the engine fan or booster stages during descent at low engine power can
shed in significant amount into the core inlet upon engine acceleration when the
variable bleed valve doors close. This ice ingestion will then increase the water/air
ratio leading to flame smothering.
This situation if not corrected can lead to the temporary loss of both engines thrust in
flight which constitutes an unsafe condition. In order to mitigate the risk of a dual
engine flame out in flight, the original issue of this Directive mandated the
operational procedure which increases the fuel/air ratio in the engine during the
descent and under inclement weather conditions.

“ICING CONDITIONS EXPECTED DURING DESCENT
• If icing conditions (including ice crystals) are expected during descent:
• At top of descent, or at the latest before entering the expected icing
conditions:
Select ENG ANTI ICE and WING ANTI ICE to ON.
Select PACK FLOW at HI.
• Below 10 000 ft:
Resume normal operation.”

[bsieker]

PJ2,

Thanks, yes, that's exactly the same wording as in the Flight Manual, which I abridged.

So the B777 protection system only reduces the likelihood of inadvertent stall, but will not absolutely prevent the pilot from pulling the column fully back. And since the engines did not respond in this case, Autothrottle would not have been able to do anything, either.

Whether or not this is relevant or whether or not being able to stall the aircraft in from the last 10' actually helped in this case, I'm basically trying to understand the Triple's systems, since up to now I'm more familiar with Airbus, but always like to know as much as I can about the machine.

This leads to another (possibly only marginally related) question: It says in the Manual that Autothrottle will support stall protection by increasing thrust as needed, when armed but not active:

How common is it in a Boeing to have the Autothrust neither active nor armed?

(The Alpha-Floor protection in Airbus goes to, and locks, TOGA thrust regardless of previous Autothrust setting (off/armed/engaged)).

Please, again, I'm not judging either over the other, just wanting to learn.

The inhibition altitudes for autothrust/-throttle supporting stall protection seems to be the same for both B and A, namely up to 400' at takeoff, and from 100' down during landing.


Bernd

[PJ2]

Morpheme;

Well sorry if I sound dismissive (which I am) but even several hours in very low temps won't send 30-odd tons of fuel below -47degC.

I concur. I would be very surprised (shocked is more like it) if this turns out to be an issue. The case of "fuel out of China" may have a tiny bit more legitimacy but as someone else has pointed out, polar and overseas routes are done out of Beijiing all the time with nil problems in terms of fuel-jelling etc. Now when things get down to, say, a steady -70C enroute, there are procedures including descent, diversion etc which are in place to handle such issues. Fuel freezing is not a significant industry issue but of course cannot be dismissed here because we just don't know yet.

[lefthanddownabit]

There does seem to be a lot of confusion over this, the AAIB report does seem rather at odds with what John Coward apparently told Sky News:

"The adrenaline kicked in when I realised I had to land the plane with absolutely no power at all. There are drills for a power failure at 30,000ft, when you have time to reset and restart engines, but there are no drills for this. As I approached the runway, I thought that this was going to be a catastrophic crash."

If an engine hangs and does not respond to acceleration demand, one way to reset it is to shutdown and relight. Maybe that's what the F/O meant.

The AAIB report does not go into any detail, so there is not necessarily any conflict between it and any statement the crew might make (though I'd rather they didn't talk to the media to be honest).

[PJ2]

looseobject;

FYI, re the AD for the GE CF6-80E1, a similar bulletin was issued for the RB211, requiring the selection of engine anti-ice as part of the pre-descent checklist.

That bulletin was rescinded in July, 2005 and is no longer applicable to the RB211.

Cheers,
PJ2

[Pinkman]

Sunfish

I have no idea whether fuel specification and freezing is an issue in this case or not. And actually, neither do you. I did say I thought it unlikely. But you just dont know. And by the way, cloud point isnt a typical specification used for Jet - its used for diesel, along with cold filter plugging point (CFPP).

But what do I know, I'm just an ex lab-rat fuel-analyst....

[Riverman]

GMDS
Granted the following AD applied to GE90's but does appear to confirm that there are paths where FADEC signals can be corrupted.


SUPPLEMENTARY INFORMATION: The Federal Aviation Administration (FAA) has received seven reports of loss of thrust control (LOTC) on General Electric Company (GE) Model GE90 turbofan engines installed on Boeing 777 series aircraft. Five LOTC events occurred in-flight and two occurred on the ground. The five in-flight LOTC events were temporary in that the engine recovered and continued to operate normally for the remainder of the flight.

Investigation

The investigation revealed that water can accumulate in the Ps3 and P3B pressure sensing system, which can freeze in the full authority digital engine control (FADEC) sensing ports or pressure line. Frozen water can result in a restriction or a blocked signal to the FADEC. This blocked signal can cause a corruption of the FADEC signal and result in abnormal engine start characteristics on the ground or lack of engine response to commanded thrust levels in flight. Although there have been no LOTC events attributed to icing of the P3B sensing system in the field, inspections have identified moisture in this system, which could freeze and corrupt the P3B signal to the FADEC as well. This condition, if not corrected, could result in LOTC due to blockage of the FADEC sense lines, which if it occurs in a critical phase of flight, could result in loss of aircraft control.

Simultaneous LOTC Events

The FAA is especially concerned about the possibility of simultaneous LOTC events on both engines installed on the Boeing 777 series aircraft due to common mode threats, such as certain atmospheric conditions that may result in ice in the Ps3 or P3B pressure sensing system and causing corrupted signals to the FADEC in both engines.

SUMMARY: This amendment adopts a new airworthiness directive (AD) that is applicable to certain General Electric Company GE90 series turbofan engines. This action requires visually inspecting Ps3 and P3B sense lines and full authority digital engine control (FADEC) Ps3 and P3B sensing ports and fittings, cleaning Ps3 and P3B fittings and sensing ports, purging the Ps3 and P3B systems of moisture, and, if necessary, blending of high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads. This amendment is prompted by seven reports of loss of thrust control due to corruption of the signals to the FADEC caused by water freezing in the Ps3 sensing system. The actions specified in this AD are intended to prevent loss of thrust control due to corruption of the Ps3 and P3B signals to the FADEC which if it occurs in a critical phase of flight, could result in loss of aircraft control.

Interim Action

Both Ps3 and P3B pressure systems incorporate weep holes that allows drainage of water in the lines that may accumulate from condensation or ingested water; however, the field events and the investigation have determined that these design features may not always be effective in eliminating water from these systems. GE is assessing design changes that will prevent water from freezing in these systems and causing corruption of the signals to the FADEC. The requirements of this AD may change based on the ongoing investigation of the root cause and field inspection results, and future rulemaking may be necessary.

[sandbank]

TALKING TO THE PRESS - LeftHandDownaBit

LeftHandDownaBit
QUOTE
"...there is not necessarily any conflict between it and any statement the crew might make (though I'd rather they didn't talk to the media to be honest)."

Hmmm...Clearly journalists and the media at large seem to be held in pretty low regard by the professional pilots on this thread - but for the life of me I can't understand why.

There's nothing special or secret about the probable causes of an aircrash - such incidents are a matter of legitimate public concern. It's quite right that aircrew should be approached for interviews and that the public hears what they have to say.

After all, what is there to hide?

[DingerX]

Just a note, playing the logic referee:

There's plenty of stuff that's "out of bounds here"; plenty of folks saying things that betray outright ignorance, not only of how these things fly, but also of what those with evident knowledge and experience say about it.

On the other hand, there are plenty of arguments that deal merely in improbabilities. The poster child for this is fuel contamination. Chances are it wasn't. Hey, if there were a case of gross fuel contamination, we'd see a much worse situation (in turns of number of aircraft affected) that what we have here. To be honest, the system is set up to prevent any gross error that would have such a result. But, right at the borderline, where odds are it won't affect anyone, a subtle degradation could provide enough profit that the slight risk that only a morning long-haul flight through the Arctic would have to make it materialize. Was it the case? Doubtful, but what isn't doubtful at the moment?

In summary: while we need to consider every possibility with extreme skepticism, when something like this happens, by definition it is an extremely rare event. Therefore, while the argument "that would be extremely rare" provides a necessary skeptical perspective, it doesn't invalidate the claim (and, for those playing on conspiracy-theory "logic", actually validates it).

[barrymung]

I would agree; fuel icing is *very* unlikely in this case.