dxzh

I see what you mean about this potentially applying to any aircraft and I am conscious that statistics can be used any which way by whoever chooses the assumptions and data to be analysed. I had not meant to be partisan in my choice of assumptions but perhaps I have introduced bias by trying to take into account the interim findings and you might be doing so if you do not take them into account?

To one person, a single incident of an uncommanded reduction in power of both engines is not, or is hardly, statistically significant in the general scheme of things and does not necessarily mean that any particular aircraft should be grounded or, as elsewhere suggested, restricted.

To another person, IF it can be tentatively assumed after investigation that contributory factors external to the aircraft itself such as crew and fuel can be discounted and factors specific to the aircraft such as the independence of the two engines is as certified, then the uncommanded reduction in power of both engines on an aircraft within seconds of each other and a failure to respond to further requests for power might be seen by many as either a highly unlikely event (if I may, equivalent to a sperm whale finding itself freefalling to earth with a bowl of petunias) or evidence suggestive of a flaw in its certificated design/performance. I accept the assumptions here are crucial.

Again I was only trying to consider, compared to many crash situations in which the airframe is not immediately recovered largely intact, the difficulty stakeholders may face in deciding not to ground or restrict aircraft (and no, I am not arguing for either) now that the initial investigations have been completed and so many of the other possible contributory factors have been tentatively discounted. As the airframe and crew survived, after a few months of investigation there seems to be a practical limit on the ability to obfuscate about the potential alternative contributory factors of the highly improbable uncommanded reduction in power of both engines, while apparently leaving those responsible for investigating, manufacturing and certificating the supply of fuel to the engines (whether in G-YMMM or other aircraft) in the invidious position of still being unable to explain the demonstrated critical failure in an otherwise highly reliable system and to make recommendations accordingly.

lomapaseo

dxzh

I may pick at your arguments somewhat, albeit they have many sound qualities. Remove the ETOPS argument above, as the issue equally applies to all aircraft operations.

Also to be pedantic, the term rollback has historically been used to describe a different malfunction scenario so perhaps we should only use the words released to date by the investigators.

continuing in pedantic mode

There is no such thing as a fluke in statistics, as their use is only a means of communicating natural occurences (combinations)

I remind that neither the designs nor certification imply all is perfect and free from catastrophic occurences. There will allways be the rare occurences of combinations not forseen nor even recognized after the fact, that will exist in aviation for relatively short periods of time (measured in risk per flight hour).

Some risk of unknowns is acceptable even some risk of knowns is acceptable over controlled periods of time. The issue is to be certain that the level of risk is within acceptable bounds and this is done by continued dilligence and investigation of potentially related events (either in history or today's)

So in my opinion groundings or flight restrictions are not evident at this time, but continued dilligence, (investigation and understanding) is appropriate.

show me the data and I will recommend the action

silverstreak

With the airline (BA), Manufacturer (Boeing) and the British AAIB-CAA etc etc involved, as well as other agencies...

Being blunt and upfront literally, -- NO offence intended to any member of the crew -- no one seems to be any further forward after almost 7 months of extreme head-bashing, early mornings - long afternoons and late nights around computer simulations, test rigs, theory upon theory etc etc etc...

No one seems to agree on any particular 'reason' for this happening. Leading on from this, when do the authorities decide to call it a day - if at all?

Is this another 'unknown' phenomenon... In which case, basically case closed...

dxzh

Thanks - point taken re ETOPS, rollback and fluke.

And I agree about living with knowns and unknowns for controlled periods - we all accept a measure of risk in living our daily lives.

M.Mouse

How do you know that?

chris weston

Silverstreak, sir.

Simply because we have no further information from AAIB does not mean that AAIB has no further information.

(i) I incline to the view that AAIB does not leak- it can't see the point of it, it's not a useful exercise from their perspective.

(ii) We do not set the time frame for AAIB reportage - a process which is currently well within their standard pattern. Look at some of the previous excellent postings on this.

(iii) IMHO we need to be patient.

The frustration v trust dichotomy is never an easy one to resolve!

CW

phil gollin

It may well be that the AAIB does not leak, but earlier in the investigation there were "leaks" from various sources.

These have dried up - maybe because discipline has improved, maybe not.

.

silverstreak

M.Mouse...

OK point taken Nothing has been done so far in the quest to find out what actually happened

M.Mouse

You miss my point. There is a massive amount of work being undertaken. The fact that details of the results of that work have not yet been released is not an indication that 'no one seems to be any further forward'.

Peter Brown

May I ask a couple of questions on the 777 incident?

What was the temp on the ground while the aircraft was on turn around in China?

What temp had it been exposed to, and for how long, while en route to China?

I understand that fuel "waxing" might be an issue. Fuel does not fully dewax for some time after landing. If an aircraft flies a long haul, sits on the ground in low temps and then flies long haul again the fuel wax status may be enough to prevent required fuel flow as deposits clog filters..?

Would it be desirable to alternate an aircraft between hot and cold destinations to help reduce the possibilty of waxed fuel build up?

Just thoughts..??

Rainboe

People get suspicious of brand new posters coming in with deep and searching questions! What was your ID before?

There was nothing unusual about the circumstances. It might have been a little colder than normal, but aeroplanes do actually operate in very cold climates all the time, and cruise for hours at extremely low OATs. Rather than simply ask, if you feel it's relevant, try a little research on your own to answer your own questions. Do you think all that wasn't examined right at the start?

Peter Brown

Well it's nice to be made welcome, thank you Rainboe, I appreciate your rapid reply.

You obviously have all the answers, and please be aware that you have no need to label me as suspicious. Most of my days have been spent in the airline industry....

I understand from your reaction that fuel waxing is not an issue? Maybe you could direct me to the latest studies on the properties of jet fuel at low temperatures.. I would be delighted to find my own answers as you have suggested I do!!!!!!

Rightbase

Peter - there is a 'search this thread' button at the top of the forum window.

Try searching for temperature specification or other words likely to be in any post answering your question.

The extracts found by Search all have a clickable link to the actual post.

Each post has a poster. If the post makes sense, click on the poster's pseudonym, then follow through to the poster's profile, and to a list of other posts by the same poster.

Note the post numbers of anything interesting, then when you refer to them in your post, your readers can find and assess the posts for themselves.

Newbies get mixed welcomes here - probably for good historic reasons.

Welcome!

Peter Brown

Many thanks RightBase

Your welcome and guidance very much appreciated.

CONF iture

I do think a 330 would have done very well with hopefully no casualty as well.
But my view is slightly different from Chris Scott view

By manually fire walling the thrust levers, Go Around Auto Flight logic is triggered.
FD bars command SRS (Speed Reference System) in this case probably VAPP (VLS + 5kt)
As speed was already around VLS or even below and as bizarre we might think FD will command aircraft to pitch down (waiting for thrust increase …)
Note: AP is still ON unless manually disconnected or sidestick manipulated.
Now aircraft is below G/S but still at VAPP.
Houses are getting closer … time to refuse ground contact by pulling the sidestick (AP now disconnects)
Speed is bleeding AOA increasing to AlphaPROT … (maybe AlphaMAX but I don’t think AlphaMAX is achievable below 100 feet …) STALL protection remains active.
Less drag in the early portion and better ground effect, aircraft touches down somewhere in the grass in a nose high attitude.
V/S at touchdown depends on pilot fortune in the overall process.

Would be nice to validate (or not) this scenario on a 330 sim if ever able to simulate the thrust deficit with THR LVR in TOGA gate.



BA038 touched down in a very flat attitude witch means it had stalled already.
Combination of soft terrain + landing gear impact absorption made things very comfortable for passengers at least.

Too bad AAIB still keeps very secretive on aircraft performances as well as on front crew actions …

Bis47

I understand very well your concern about the "temperature history" of BA38.

I follow this thread since post # 1 and I didn't get documented data about ground and flight temperatures the aircraft met during the flights and the days before.

We know that there was no "fuel draining" before the flight to London and that there were some fuel ice messages.

We know also that the flight was operated well higher and colder than initially planned, and that the crew didn't ask for descent into warmer temperatures over eastern Europe while other aircraft did. That's about all ...

I just hope the investigators are looking carefully into weather records.

In my past career, I got my share of temperature related problems with fuel, fuel systems and other aircraft systems as well, all in duly certificated aircrafts and components. And yes, at some points, we had to switch aircraft on cold sectors.

Welcome!

Green-dot

Bis47:
However, water draining checks were performed just prior to refuelling for departure to Beijing on January 15th (see AAIB special bulletin S1-2008, page 5) and could you please explain when those "fuel ice messages" were presented to the crew? These are not mentioned in the AAIB reports.


Thanks and regards,
Green-dot

dxzh

@Bis47, I guess your "fuel ice messages" reference is to the unverified report on pilotsofamerica.com forum (see UPDATE on the LHR (Heathrow) 777 incident - Pilots of America Message Board) on 30 January 2008 (and picked up by blogs elsewhere) as to the theories being investigated by the AAIB. One theory the unverified report mentions as being investigated is that:

"Ice in the fuel somehow limiting the fuel flow to the engines. A maintenance message indicating excessive water in the center tank was set during taxi on the two previous flight legs, although it cleared itself both times."

For what it is worth I note that the unverified report was introduced by the words "Aspects that the FAA believes the investigation is concentrating on are: [...]" but also that the alleged fact re maintenance messages is not mentioned in any AAIB statement published to date (whether Statement of accident, Initial Report, Initial Report Update, S1-Report or S3-Report).

Assuming ice in the fuel was being investigated at the time, it seems less likely to be relevant now given the subsequent analysis and AAIB statement in its S-3 Report that: "The fuel has been tested extensively; it is of good quality, in many respects exceeding the appropriate specification,and shows no evidence of contamination or excessive water".

@Peter Brown, you might also have a look at articles re flight in polar conditions at Aero 16 - Polar Route Operations and on fuel temperature data on polar flights at http://www.fsinfo.org/FSI-journals/4q_2000.pdf.

Swedish Steve

There is no fuel ice message on the B777.
There is a water in fuel message. However this is never presented to the crew. It is hidden away at the bottom of the fuel qty maint page which few people ever look at unless you have a fuel qty problem. However it is stored in EICAS NVM so can be seen by the investigators.

Green-dot

Exactly.
That is why i wondered how Bis47 came to such a conclusion.



Green-dot