Originally Posted by
Green-dot
FAR 121, App. M, Item #43. Additional engine parameters:
There are several parameters such as vibration level, N2, EGT, Fuel flow, N3 and:
Fuel cut-off lever position. Is this the only parameter that is recorded to determine spar valve position? FAR 121, App. M does not mention any (required) parameters for recording spar valve position other than fuel cut-off lever position.
Modern DFDRs can record hundreds (if not 1000+) of parameters - way more than the minimum required set, plus they have the QAR (which may record even more) for almost all of the flight (including through the onset of the problem).
I think it is highly likely that the AAIB have spar valve position data, their statement is that the data shows valve open, not indicated open or commanded open. They also state that movement (even uncommanded) "would have been recorded", which implies to me that there are FDR parameter(s) recording actual position as well as commanded.
If the premise is that spar valve control has been tested and could not be demonstrated to fail under any condition, would the tests (investigating BA38) have been a duplication of tests performed during certifiation of the control system? If so, would there have been a reason to add any FDR parameters other than the required fuel cut-off lever position to determine spar valve position if the system was tested as fool-proof during certification?
They don't actually state that they couldn't make it fail, they state that they couldn't reproduce "uncommanded
and unrecorded" movement (my emphasis) - which is actually quite a different premise. They then infer that there was no failure because none was recorded, rather than because it was failure proof.
Referring to warning enunciation on the flight deck regarding spar valve position. The warning I am aware of is presented only when there is a disagree between [...]
I don't know enough about 777 instrumentation to be sure, but I believe that on older boeing types there was(is) a spar valve light that indicates closed
and transit. It would be interesting if that has been lost (or relegated to a maintenance page) going to glass cockpit. However, I also think that the AAIB must have some basis for their statement that warnings would have occurred.
It would have been interesting if the FDR parameters (and which parameters) for the spar valve positions were included in figure 2 of the interim report. Perhaps they will be included in the final report.
I agree - but on the other hand they may regard a flat line graph as superfluous if they believe they have already stated the same in words.
Don't get me wrong, I quite liked your spar valve theory, and the AAIB clearly also thought it was a line worth investigating - but I do think it is looking a little dead now.
[I have to admit I don't like the ice conclusion, I feel I need to re-read and digest the report a bit more, but it does seem to be what's left when they've eliminated other things, rather than driven by positive evidence. Feels very unsatisfying as a conclusion (even interim).]