bsieker

Chris Scott has already speculated about what a similar scenario would look like in the A330. It's an interesting read.

The result would have been very similar, except for an earlier AP disconnect, shortly after setting the thrust levers to maximum (TOGA) thrust.


Bernd

Jo90

I must have missed that. As you say - interesting.
Thanks

Jo

dxzh

Two questions, the second of which is hopelessly naive but seems important to address if only to rule out:

1. Has anyone yet any confirmed example of any cavitation-induced damage to similar HP pumps on a Boeing?

2. Why is there now no presumption of a latent serious design flaw in G-YMMM and the 400 or so similar B772ER aircraft, given the tentative findings that G-YMMM was apparently operated within a normal flight envelope by competent crew with the correct spec fuel?

My initial view on the second question after the last AAIB report came out was that not grounding similar aircraft to the one with a demonstrated but inexplicable fault in which two out of two engines fail to generate sufficient power while on finals over heavily populated areas into LHR was arguably a bit like dismissing the fact that there is an elephant in your nan's living room - whether on the part of crew, SLF, the families under its flight path, manufacturer, regulators, governments, etc. As demonstrated, the flaw would seem to manifest itself at low altitude when most of us would agree that there may be no or severely limited options to extend the glide or land elsewhere.

However I have come around to the view that it is reasonable that commercial issues dictate that a plane with a latent design flaw continues to fly until testing or at least two accidents can demonstrate that the flaw exists in a way which is more than just an unfortunate and mysterious fluke, particularly given the otherwise unblemished record of a workhorse of a plane with a huge number of trouble free sectors. A probability driven analysis of a possible "catastrophic" failure repeating itself would seem to be the most rational aviation industry response consistent with the prime objective of safety as with other risk assessments associated with flying.

There does seem to be a danger though that, by giving a nugatory risk weighting to a likely repetition unless and until someone can prove the causal mechanism behind the flaw/fluke, the industry profits from continuing to fly these aircraft with the regulators' approval and such a rationale in the face of any future catastrophe is looked on with hindsight as being more cynical than sensible on the part of the various stakeholders tacitly or otherwise supporting it.

Re-Heat

So you suggest they ground an aircraft without knowing what caused the crash? This was debated 5 months ago on these forums, and overwhelming deemed to be totally imprudent.

You cannot enitrely avoid risk anywhere, and to try to do so would set us back in the stone age. Live with it.

precept

I generally agree with DXZH on the question of flight certification of the aircraft which failed to operate safely within the allowable envelope. From my perspective, the TMS 777 as configured, should not be certificated in environmental conditions which resulted in the accident unless and until it can be demonstrated that such operation is safe.

The 777 is a great aircraft. Nevertheless, it failed to operate safely under conditions which resulted in the LHR accident. Given no other data, information or analysis, it seems to me that the 777 must be restricted from commercial operation which approximate and exceed the adverse atmospheric conditions experienced by BA 038,

(TMS - Type, Model, Series)

TD

lomapaseo

To restrict or to otherwise remove the certificate of airworthiness implies that you have probable knowledge of the the degree of restriction necessary or violation of the original certificate.

That has not yet been concluded by the investigation or the regulator

It was presumed that any fleet entering service does so by carrying a degree of latent unknown risk. Historical hindsight has shown that this degree can vary over time with some risks maturing into known risks which are then addressed over time by minimizations and corrective action programs, while still newer risks develop.

The issue is not which ones are latent unknowns and which ones are known and being addressed over time, but rather the question is how much risk is being carried over what period of time.

Restrictions and/or groundings are decided on the level of risk and not just whether the total risk causes are known or unknown.

chase888

Unfortunately, everyone is waiting for someone to scream EUREKA, the problem is solved.

Interestingly, in flight shutdown events have subsided with the onset of the Northern summer?

It would be a very simple, low cost palliative to introduce a bit of heat into the tanks near the feed pipe which would ensure that ice/wax is eliminated from future possible occurrences.

Not very scientific, but IMO "prudent"

Leodis737

Well that is an incredibly frank and honest statement.

Thinking about it, what other options do FAA/EASA have? Slice something off the environmental envelope of the plane as a precaution? Require that the engines be run up at least once during a CDA approach?

One thing that gives me hope is that there are precedents for extremely improbable failures being diagnosed years after the initial accident: e.g. UA585 and US427 ... the NTSB reports were finally adopted 10 years and 5 years after the accidents, respectively.
http://www.ntsb.gov/publictn/2001/AAR0101.pdf

Fingers crossed, but not holding my breath.

snanceki

This incident had a cause. Period.
The consequences could have been extremely serious if the issue had occurred just a few moments earlier.
If it has happened once, it can happen again, unless something changes. Period.

The fact that the cause remains unidentified must remain as a significant concern.
IMHO and from what we have surmised sufficient data exists to implicate a combination of fuel / fuel delivery system / and environment.
Therefore I would have expected some form of interim procedure / system change to have been introduced to reduce risk until a full explanation is unravelled.

The most surprising omission IMHO is why increased fuel temp monitoring / modified temp threshold value / increased water drain off frequency (or conditions) does not appear to have been introduced, at least on this sector or with this operator.
Maybe such an action has been taken although not reported.
Such an action would be a low cost "palliative" and would also add to data collection.

IMHO I still suspect the "fuel" (i.e. including water from the CWT) in combination with other factors.
Not that it was out of spec, but that the current spec(s) / procedures are too loose in some way.
Its the only thing that was truly common to both systems.

pax2908

As I understand, one of the factors in this accident was that the problem was recognized late, with very little time to react. Would it be possible (reasonable?) to change the procedures so that this kind of problem can be found earlier, for example by avoiding "long" periods at reduced thrust?

dxzh

I am sorry for not making myself clear. I am not currently suggesting that the plane be grounded - quite the reverse.

However, the recovery of the aircraft largely intact and 5 months of investigation seems to make the decision not to ground the aircraft more difficult. This is because the tentative dismissal in the several months since the crash of the extraneous factors that would typically cloud the issue (eg crew performance, operation outside flight envelope, component failure, out of spec fuel, etc) makes it more likely that the flaw/fluke is a design issue.

Again, I apologise to you for not making myself clear but I strongly agree with you that a risk based assessment is the only sensible way to proceed.

Nevertheless I believe what would be imprudent conduct as you succinctly point out without evidence may become less imprudent (or even become prudent) if hard evidence seems to eliminate the other obvious possible causes, notwithstanding the causal mechanism of the flaw appears improbable and is not understood.

cwatters

> Would it be possible (reasonable?) to change the procedures so that this
> kind of problem can be found earlier, for example by avoiding "long" periods
> at reduced thrust?

Perhaps but I don't think we know enough to say that whatever caused the problem can only show up after a long period at reduced thrust.

bsieker

As all accidents, it had a number of causal factors. Never only one single cause.

Fuel temperature:
And:

As to fuel and water ...

... and:

If water from the centre tank had played a role during the final approach, it would have to have melted earlier during approach to be scavenged by the main tank scavenge pumps to the main tanks, and thus water would have to have been present in the main tanks. This was not the case.

(I take it that the term "significant quantities" implies such a quantity that it might exceed the operating limitation of the water scavenge system (which is effectively a fuel/water-stirrer), the fuel delivery system, the pumps, and the engines.)

And what symptom, exactly, would this "palliative" treat?

Seen another way, it would be an additional cost, with no benefit.

Still not entirely out of the question is a software problem. It is very remote, but so is every other possible scenario that has arisen so far.

If we exclude every possibility that is "very remote", we must conclude that BA 038 landed safely.

Or, according to a well-known German poet:

(A translation from Christian-Morgenstern.de:

The Impossible Fact

[...]

And he comes to the conclusion:
His mishap was an illusion,
for, he reasons pointedly,
that which must not, can not be.
)


Bernd

tanimbar

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

We have already speculated on some form of directive/restriction on ETOPS being issued before the onset of the northern hemisphere winter.

The AAIB might not issue such a document until:
1) the northern hemisphere, summer, holiday season has passed,
2) the Beijing Olympics are over,
3) all interested parties are in agreement with the need for restrictions,
4) and, the AAIB has determined that its investigations are unlikely to find a cause and solution before the northern winter.

And, maybe, we should not be surprised if the restrictions apply to all aircraft, not just Boeing 777s. That way the authorities create a commercially level playing field; probably a prerequisite for success with point 3 above.

Much has been written recently, on this tread, about the acceptance of risk. I cannot pretend to understand the basis for the statistical arguments for the low probability of a second occurrence of the BA038 incident but I remind myself that, for example, a 1 in 100 year event can occur in any year, i.e. there could be a second occurence in 2009. That's called Sod's Law.

And, I suspect that even the most competent, and confident, investigating statistician or engineer might, on hearing that his children or grandchildren were about to fly across Siberia in January-March, suggest they take another route, or have his/her fingers crossed all the way.

Can you engineers truthfully say otherwise?

(I apologise for using emotive phrasing and for appearing to attack engineers - not so; the words are chosen to highlight our collective complaisance or, in too many cases, cynical avoidance, regarding the proper understanding of risk assessments and the probability of recurrence.)

On another matter, pilots, as I understand them, have a highly developed understanding of Sod's Law. Basically they are aware, individually and collectively, that luck can run out at any time. Therefore I would be fascinated to learn if pilots have already altered their flight management behaviour, for example, spooling up the engines on descent a couple of times - just to make sure! As I've written before, better to discover a problem with a few thousand feet to spare rather than 720.

Regards, Tanimbar

dontdoit

Which all falls squarely on its arse when you realise that in a business where the words cannot often be used to their full and proper extent, the AAIB really are one of the last bastions of consummate professionalism, unlike some other large organisations we could mention. "Until after the Olympics"? Are you having a laugh? This isn't the Press Office of the Labour Government we're dealing with...

tanimbar

Granted that the AAIB might be "one of the last bastions of consummate professionalism" it nevertheless does not operate in a vacuum.

I do not denigrate the integrity of the AAIB by my comment about the Beijing Olympics. If the activation of restrictions is not required until the onset of winter why not avoid false, unwarranted passenger hysteria by delaying the release of the publication until after that event. That's just common sense and would support your view of the AAIB as consummately professional.

regards, Tanimbar

netstruggler

dxzh wrote

You're assuming that because G-YMMM was affected it must have been particularly prone to such a failure(whatever it was).

From a statistical point of view this is not a valid assumption and the incident might actually be equally likely on other aircraft types.

We're talking tiny probabilities here and a single incident is not statistically significant.

So ithout some idea of the cause it would be difficult to justify taking action against a single aircraft type.

FullWings

Well said.

You could also add that if you restrict/ground a particular aircraft type over one incident and subsequently are unable to find anything in particular that is wrong with it, how do you logically go about de-restricting/un-grounding it? Nothing has changed in the interim yet you'll have to make a 180deg. turn in terms of decision making whilst in possession of the same facts...

This also impinges on why there are no significant procedural changes in the operation of the aircraft. If you don't know what caused the problem, how can you know if your 'solution' is making things better or worse? Airlines and manufacturers are reluctant to provide 'instant fixes' as they often come back to bite them through the law of unintended consequences.

At the moment we don't know if what befell MMM was because of:

a) something unique to that airframe
b) something that could happen to RR-powered 777s
c) something that could happen to all 777s
d) something that could happen to Boeing aircraft
e) something that could happen to all commercial jets
f) etc...

Brian Abraham

Who was it that said "Sometimes the dog of fate simply lifts its leg and pisses on the leg of science." Ernie Gann?

neville_nobody

The quote is as follows from Fate is the Hunter: