phil gollin

I am extremely dissatisfied -

Having worked my way through the report I still do not understand two issues :


1: Why are the restrictions only to apply to Rolls-Royce powered aircraft - there seems no logic or evidence ? There seems no specific reason to restrict the recommendation to Trent powered aircraft other than there have not been the equivalent tests carried out on 777s powered by other engines. Could someone explain ?


2: Obviously they seem to have been able to show that the cavitation damage can be caused in the laboratory by having approx 95% of the cross-sectional area blocked.

However, they also detail the series of engine accelerations during the final approach and, indeed, state (under one assumed scenario) : “Testing by the engine manufacturer has shown that sufficient ice accretion could not have occurred on the face of the FOHE or the LP pump inlet, prior to the final series of accelerations. If it had, then the rollback would have occurred earlier during the first acceleration of the final approach series”.

The other assumed scenario includes the statement : “In this case the ice might then travel and be ‘caught’ in the pipework, spar valve, LP pump inlet or on the face of the FOHE, thereby causing a restriction to the fuel flow” but fails to state how this could have happened so close together in two separate systems and to almost exactly the same degree (1.06 versus 1.07).

There seems no scenario or explanation laid out in the report that actually takes into account the actual occurances, i.e. the slight delay in the two engines rolling back - BUT the nearly identical rolled-back thrust. This would imply that a completely unknown icing phenonomen occured in two separate systems (obviously facing the same climatic conditions) but was so disimilar that the roll-back occured a few seconds apart, but so similar that the rolled-back thrust were almost exactly the same 1.06 and 1.07. This icing effect must have been pretty remarkable to affect the engines both differently in time, but similarly in effect.

The report doesn't really explain anything and seems to be grasping at the only thing it can reproduce.

As I said, I am dissatisfied.

GemDeveloper

From memory, it's diethyl glycol monoethyl ether. If it's less than 0.02% by volume, then the fuel supplier doesn't have to seek agreement of the customer. However, if it is agreed that it is used, then the concentration is supposed to be between 0.10% and 0.15% by volume.

FullWings

borghha,

From P.12 of the interim report:

From P.11:
I take that to mean that nothing gets colder than TAT-3, though I stand to be corrected...

phil gollin,

See my previous post #1723 for quote of Safety Recommendation 2008-048

stadedelafougere

At least one of the two main aircraft manufacturers is carrying investigations on icing and behaviour of the fuel system at low/very low temperatures.
The presence of water (even in small quantities) is also problematic.

The report states that icing under -20°C is not known. Ice crystals do not behave like they do at -5°C or in your freezer.
This interim report is not surprising and does not firmly give a cause to this accident. But the effect of icing should not be underestimated.

tanimbar

Warning: I'm non-professional; not crew, not engineer - just scientist guest and thanks.

I've only speed-read the report so far but wanted to make a couple of points.

Previously I wrote,
Some here took exception to these remarks, especially the point about the Beijing Olympics. I want to reiterate that I was trying to think as the AAIB might and was not being sensational just for the sake of some silly notoriety on this thread. I now suggest we can applaud the AAIB's professionalism and look forward to industry-wide support for sensible restrictions this coming winter.

On another matter. The AAIB interim report states (Water ice in fuel, p12),

I read this with disbelief. The words, "little is known" is, well, shocking.

Until today I had thought that the industry had fully experimented, tested and evaluated the effects of temperature on fuel (at all operating ranges).

By the way, my money is still on stratification ( no, don't respond to this; I need to read the report more carefully and may change my mind).

Regards, Tanimbar

phil gollin

Full wings :

See my previous post #1723 for quote of Safety Recommendation 2008-048

Precisely, The AAIB seem to restrict their requirements to Trent powered 777s solely because they haven't done the equivalent tests on 777s powered by other engines, without any logic or explaination why these other aircraft would be immune from what might have occured to the accident plane.

Doesn't make sense to me, maybe someone can explain how a (so far)one-off icing condition will only affect Trent powered 777s ?

.

lomapaseo

Phil Gollin

very astute

maybe we need a coin tap test on the fuel-oil cooler

Rainboe

zzzzzzzzzzzzzzzzzzzzz

chris weston

As an academic pureish chemist I applaud the clarity, thoroughness and measured tones inherent within this interim report. As ever, impressive stuff from the AAIB.

I have learnt that with 20 20 hindsight "on", I suppose it's blindingly obvious that water - even at the ppm level and at levels well within the fuel's spec, can be a problem if there's enough of the fuel being cold soaked to generate enough ice to block the HP pump inlets.

I will do some sums when I have a little more time.

As has been pointed out already, the implications of all this could be far reaching. Fly lower when it's "cold" is obvious but we shall need to redefine parameters based on proper data and there looks to be a lot of work to do here.

Fuel costs will be likely to rise and be yet another pressure on ticket prices.

CW

Phil Rigg

Phil G. - Indeed, an astute observation that the almost identical failure of two virtually independent systems within seconds of each other has the AAIB considering the probable root cause to be a hithertobefore completely uknown icing event occurring identically and almost simultaneously in both of the independent systems.

Iomapaseo - The report shows a schematic diagram of the fuel system which indicates a separate Fuel-Oil Heat Exchanger (FOHE) for each of the two independent engine/fuel systems which suggests that both FOHEs would had to have failed identically and almost simultaneously should FOHE failure be the cause.

Phil G. - With regard to a one-off icing condition affecting other certificated aircraft ,then in fairness to the AAIB and as quoted and pointed-out by FullWings, their published Safety Recommendation 2008-048 does state:

"It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency should take immediate action to consider the implications of the findings of this investigation on other certificated airframe /engine combinations."

It would seem appropriate for the investigation to be considering root causes that would more plausibly (than prior unknown icing on this aircraft) cause both independent systems to fail identically and almost simultaneously. For example, causes that are common to both systems. Although it does appear from the continuing "data mining" exercise that the low temperatures for long time periods experienced on this flight do place it at the extreme end of all known flights for this aircraft type.

barit1

I'm not sure this adds up. The "amazingly efficient" Trent with more spools, and more bearings, probably has more heat generated in the oil, and thus any "stagnating" fuel will be exposed to more BTU transfer, leading to LESS probability of icing in the fuel-oil heat exchanger.

Often the most severe design point for the cooler is early in descent, when lube heat rejection is still high, yet fuel flow (the heat sink) is very low.

snowfalcon2

As far as I understand, fluid dynamics is a field where science has not yet reached even close to the near-100% understanding that we have about mechanics, to name one example. Remember chaos theory: a minute difference in the input conditions can cause huge differences in the result. Maybe the sun had warmed the left (south) engine 0.049 degrees more, requiring an additional chunk of ice before the left engine's fuel flow was restricted. We just don't know yet. But I've seen enough strange ice and slush formations in nature to appreciate that it's not a simple thing to research.

shamen123

Erm, money?

ZOOKER

Interesting intrim report.
Lots of technicolour graphs!
No CVR Transcript.
Have I missed something?

lomapaseo

Its a corollary to Occam's razor.

When the most complex of causative explanations are chosen to explain an accident the most simplest of corrective actions should be chosen to address it.

In the end it has the same liklihood of being correct

snowfalcon2

No, but the crew's conversation is hardly relevant to the the root cause of this accident.

It becomes interesting when looking at how they handled the emergency, but that's a secondary topic to the investigation, despite all the discussion of possible "stretching the glide" we've had in this thread. Hopefully it will be addressed in the final report, but the most urgent thing is to clarify the root cause.

FlyingOfficerKite

A pilot must ensure that the flight can be safely made.

Is this pilot error?

NO!

It just proves that we cannot cater for all eventualities all of the time.

Our knowledge of aviation is not absolute and on this occasion it caught us out.

FOK

nhs

FOK
As SLF I think think this is not pilot error.

However it does show that good training & good skills from flight crew can save a situation which might have led to ++ fatalities. Nothing prepares for all eventualities but learnt skills go a long way to helping.

nhs

beamender99

FOR IMMEDIATE RELEASE: September 4, 2008 SB-08-37


Washington, DC - National Transportation Safety Board Acting Chairman Mark V. Rosenker today praised the work of all the investigators looking into the crash of a Boeing 777 at London's Heathrow Airport in January, saying that the recommendations issued today "show how international cooperation can lead to safety improvements that benefit the aviation community worldwide."
The United Kingdom's Air Accidents Investigation Branch (AAIB), which is leading the investigation into the January 17, 2008, accident in which a British Airways Boeing 777- 236ER landed short of Runway 27L at London Heathrow Airport, issued an interim report today on the progress of the investigation.
The interim report contains recommendations aimed at addressing a circumstance identified by investigators relating to Rolls Royce-powered Boeing 777 aircraft. The investigation has shown that both engines lost power in the final minute of flight because the fuel flow to each engine was restricted; most probably due to an accumulation of ice within the engine fuel feed system. The ice is likely to have formed from water - which exists naturally in the fuel - while the aircraft operated for a long period, with low fuel flows, in the cold environment associated with high- altitude flight.
In accordance with established international arrangements, the National Transportation Safety Board, representing the State of Design and Manufacture of the aircraft, appointed an Accredited Representative to participate in the investigation. The Accredited Representative is being supported by a U.S. team that includes NTSB specialists, the Federal Aviation Administration, and Boeing. Rolls-Royce, the engine manufacturer, is also participating in the investigation. British Airways, the operator, is cooperating with the investigation and providing expertise as requested by the AAIB.
This interim report updates and provides further details on the history of the flight and the research done by teams in both the U.K. and U.S. using data obtained from the accident aircraft, and similar aircraft in the British Airways fleet.
The report further details the aircraft fuel systems and describes testing performed in laboratories, on an adapted fuel rig using actual aircraft components, in an engine test facility, and on an exemplar engine. In conclusion, the report provides recommendations for both interim action and longer term changes to certification criteria.
Acting Chairman Rosenker stated, "When it comes to aviation safety, there are shared interests that transcend national borders." Rosenker noted that the U.S. Accredited Representative and technical advisors fully participated in the development of the factual material and supporting research and that the recommendations are supported by the U.S. team.
The investigation team indicated that a change to the fuel system design would make the system more resilient, but would take time to implement. Therefore, to reduce the risk of recurrence interim measures need to be adopted until such design changes to the fuel system are available.
Therefore, the AAIB recommends that:

• The Federal Aviation Administration and the European Aviation Safety Agency, in conjunction with Boeing and Rolls Royce, introduce interim measures for the Boeing 777, powered by Rolls Royce Trent 800 engines, to reduce the risk of ice formed from water in aviation turbine fuel causing a restriction in the fuel feed system (AAIB 2008-047), that
• The Federal Aviation Administration and the European Aviation Safety Agency should take immediate action to consider the implications of the findings of this investigation on other certificated airframe/engine combinations (AAIB 2008-048), and that
• The Federal Aviation Administration and the European Aviation Safety Agency review the current certification requirements to ensure that aircraft and engine fuel systems are tolerant to the potential build up and sudden release of ice in the fuel system (AAIB 2008-049).

Green-dot

A very informative and well written interim report. It answers many questions with respect to findings on several systems and subsystems.

Specifically with reference to the spar valves, such as their possible uncommanded movement being a recorded FDR parameter, therefore ruling out the possibility they contributed to the cause to this accident. I assume the FDR recordings of the spar valves parameters implies any movement from the open position is recorded, even if they were to only partially close (up to 95%?) and not reach the fully closed position before opening again.

Of course I leave it to the experts in charge of the investigation but I do wonder what is meant by extensive testing of the spar valve control system. Was such system bench tested only or were such tests also conducted with the control system installed in the subject aircraft in conjunction with other aircraft systems operating? And regarding HIRF and EMI, to which power levels have these tests been conducted since the report only states "well in excess of published standards . . ." Perhaps the final report will be more specific.

Furthermore, I am not convinced if, in the event of uncommanded movements of the spar valves, a warning will enunciate on the flight deck under all circumstances as mentioned in the report. But that issue seems irrelevant now since all indications are that the spar valves worked as advertised.



Regards,
Green-dot