bsieker,
Who said anything about fly-by-wire? The subject of my post was thrust lever control; nothing else. What I am talking about is a well known FADEC phenomenon called rollback. You don't seem to be familiar with it or else you wouldn't swallow the fuel valve open preliminary investigation comment so gullibly.
Whether you know it or not in FADEC, code algorithms are constantly checking engine parameters and "voting" when, or if, to schedule twin spool acceleration. Since they won't allow overboost, and are concerned about thermodynamic engine life they sometimes reject a flight deck command in favor of a slower acceleration schedule. (Most of the time this is a good thing.) Sometimes they reject everything altogether and command idle logic instead (which can't happen with old 747-100's and 200's with steel cable to hydomechanical control.) Thus my position that the old design was safer from a "fail safe" consideration at spool up. A thrust lever cable breaking is extremely rare. In over twenty years of flying them I've never met anybody who's had it happen. But I have met pilots who have had unexplained rollbacks using FADEC.
bsieker, A snapshot (data point) of the sun in the sky does not mean it is daylight 24 hours a day. Fuel valve positions can be momentary recorded in the middle of transitory problems; so this report of everything being fine with the fuel valve means nothing to me.
Here's what one of the so-called "experts" who writes in aviation rags has to say:
a software glitch affecting the engine control system is among the possible causes being investigated.
An interesting article dating back to October 2006 (
http://www.iasa-intl.com/folders/bel...rustworthy.htm), focuses on errors introduced with a FADEC (Full Authority Digital Engine Control) software update that affected the B.777 equipped with GE90 engines. The article reports about two thrust rollback recorded on the 777-300ERs that suffered the failure during take off (and 5 occurred in flight). Subsequent troubleshooting found that the rollbacks were caused by a glitch in the software of the FADEC and that the reductions “only likely to occur at reduced powers”. The article explains that the flawed software was installed after a FADEC software update.
So, the FADEC has already caused worries to the B.777 operators using GE engines. The British Airways aircraft was equipped with RR Trent engines, even if the software used to control them is probably the same (or mostly similar). Even discarding the possibility that the current software may still cause Loss Of Thrust Control or LOTC for the same flaw (the AD was issued in 2006 and by now the software should have been patched), the above mentioned article provides also details dealing with an Airworthiness Directory applied to the GE90 engines that confirms the risks of corruption of the FADEC signals because of clogging of the sensors feeding the engine control system. The GE90 engines incorporate now a design modification aimed to prevent signal corruption but what about Trent engines?
For pictures and a more in-depth analysis, I suggest visiting this link that was provided from a visitor:
http://www.iasa.com.au/folders/Safet...38_LikelyCause
BA038 crash landing caused by a software glitch? « David Cenciotti’s weblog - the most visited Italian Aviation Blog
bsieker said:
Btw, cables can break, and need constant re-adjustment due to lengthening, and on multi-engine aircraft all enginess are never adjusted equally leading to thrust-lever staggering in normal operation to get them all to the same power output.
Seperately, who cares about staggered throttles? It doesn't hurt your flying ability to be a knob or so out of rig. But it does hurt your flying ability to have microsoft windows type crap software between you and the spray nozzles. No way to override it in time. Bad Bad design, imho. But that's how were doing it now.....
BTW, I was just being melodramatic to underscore a point. If I only got on non-FADEC controlled aircraft, of course I'd never get anywhere.
Regards