CONF iture,
I am certainly now prepared to give more credence to the "apparently leaked" FAA memo dated 24 January 2008 (which popped up on the internet by 1 February 2008). This is because the purported inside knowledge in the memo of what seemed to be non-public, pertinent information at that stage of the investigation has been subsequently corroborated in many varied respects by information in the AAIB's later bulletins and reports. Was the memo as leaked only a draft (or even a forgery) I do not know - however, I try to note well the cautionary words drummed into us by PPRuNe about not taking everything at face value and hence I wrote "apparently". The memo itself ends with the words "Information only. This information is preliminary and is subject to change". If very curious about the memo's provenance, maybe the answer is for some brave soul to pick up the phone to its supposed author, Doug Pegors, and ask him - his direct line at the FAA is publicly available.
As regards the AAIB reports to date, I believe they are concise and well-written, concentrating correctly on the contributory factors to the underlying accident, rather than the consequent events as the aircraft impacted the ground. Actions at the time of impact may not be wholly irrelevant in so far as they may reflect on the status and set-up of the aircraft on or prior to the underlying accident. However, the key concern here is to understand the unheard of rollback of each of two seemingly fully-functioning engines at a critical stage of flight. I am not surprised that the AAIB's clear focus is on understanding the duplicated rollback and how to avoid a double failure condition in the future.
There are clearly gigabytes (let alone pages) of raw data and analysis which could be made public but that would be a disclosure exercise of an altogether different quality and for a very different purpose - this investigation is not the subject of some hugely expensive public enquiry or court case (thank goodness) and, as ever, safety in aviation has generally benefitted from measured disclosure of facts concentrating on solutions and not scapegoats and thereby encouraged full and frank offline discussions with accident investigators (rather than a**e covering for fear of litigation and a blame culture). The AAIB has already disclosed much more than it might have, but given the degree of rumours and speculation perhaps a balance has had to be struck.
Am I surprised or concerned that I have not received a download of all the data in the QAR, FDR and NVM or test rig papers etc? No. Am I surprised or concerned that the AAIB may omit from the 21 page interim report certain information about events which I assume the AAIB is confident happened on or about impact (perhaps technically part of flight until aircraft stationary, perhaps interesting to a pilot, but not relevant to the focus of the investigation)? No. Am I concerned that information in earlier AAIB bulletins such as about FOD (eg plastic scraper) has not made it into the interim report? No. In fact I really believe the AAIB is doing a great job synthesising the information and keeping the correct focus on the critical failure condition.
Nevertheless, I do speculate about the uncorroborated centre tank messages even though I can understand why if they did exist the AAIB might have discounted their evidential importance given the sumping and, perhaps, a suspicion that the message is not as reliable as it might be and it would consequently be misleading to draw from it a conclusion that there really was 600+ litres of free water in the centre tank! On the point of water in the centre tank (as opposed to the omission of messages (if there were any, I stress) from the interim report), I feel a little rebellious as water in any tank bears on the underlying accident, even without any suggestion of such a message, and to my mind there is circumstantial evidence in the design and track record of 777 centre tanks suggesting a tendency to accrue ice and free water there. There is even in the (apparently leaked) FAA memo a second statement of information learnt on 22 January 2008 that "There was a message of water in the center fuel tank shortly after departure from Beijing." - ie implying that not just on the two previous legs, as learnt on 24 January 2008, but on the actual accident flight there might have been some ice which melted into free water in the centre tank. I could envisage a scenario along the lines of: existing ice already in the centre tank is gradually melted following the uplift of warm RP-3 fuel; the resulting free water triggers a message; and sufficient free water is then dissolved back into the bulk of the fuel by the water scavenge pumps' operation to clear the message.
As to the APU start sequence (around termination of QAR recording) and cross feed valve, I am very curious and have lots of questions and ideas, but I personally see little relevance to the real focus of the investigation even assuming as I do what is stated in that apparent FAA memo is not complete fiction - to the extent either were involved in events after the dual rollback process had started, I strongly suspect that the AAIB would see them as playing a secondary role and the data bears out that there was a much bigger issue already playing out - namely a critical restriction in both fuel lines.
Last edited by dxzh; 9th September 2008 at 01:02.