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| C2H5OH
June 13, 2025, 11:32:00 GMT permalink Post: 11900388 |
One has to assume that, given the seeming lack of lateral deviation from the flight path, and with no obvious yawing or rudder input visible on the videos, there's only two realistic conclusions here? Simultaneous dual engine failure of unknown cause if the RAT was indeed deployed; or flaps reduced too early leading to a stall if the RAT wasn't deployed.
Evidence in this thread would lean me toward the RAT deployed and therefore dual engine out scenario. As for the cause of that, well, only a couple of likely scenarios exist that could cause simultaneous shutdown of both engines, including mistaken or intentional use of the fuel cutoff levers. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All) Fuel (All) Fuel Cutoff Fuel Cutoff Switches RAT (All) RAT (Deployment) |
| C2H5OH
June 13, 2025, 16:50:00 GMT permalink Post: 11900685 |
Former Boeing Engineer, actually worked on this specific airplane prior to delivery.
\x85 2 is the only one I haven't seen mentioned here and I say this as a no longer Boeing employee. We STRUGGLED with AI during the EIS. They were notorious for just parking airplanes and then using them as spare parts and then screaming for help when they had to go back and get the planes ready to fly again. So what kind of maintenance errors could AI possibly make, that would not cause a Christmas Tree of BIST errors during startup and preflight and crash the electrical system of the aircraft right after wheels off? Subjects: None |
| C2H5OH
June 15, 2025, 20:06:00 GMT permalink Post: 11902782 |
As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.
So I wouldn't vouch for the FADECs if there was catastrophic problem with the power distribution in the aircraft. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) |
| C2H5OH
June 15, 2025, 20:10:00 GMT permalink Post: 11902783 |
TCMA is on both the Trent 1000 and GEnx-1B 'basic' - it was required for certification. There is no reason for TCMA to be listed in the MMEL as the only 'functional' portion is the via the electronic overspeed protection system (which is required for dispatch - no MEL relief) - the rest is software resident in the FADEC.
Where does that piece of software reside by the way? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC MEL |
| C2H5OH
June 16, 2025, 06:54:00 GMT permalink Post: 11903156 |
And most of all, the SISO principle (#### in #### out) applies with regard to data from other systems, which are obviously processed in TCMA. Multiple transient faults may not be considered comprehensively e.g. in input processing and filtering.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC |
| C2H5OH
June 16, 2025, 08:26:00 GMT permalink Post: 11903751 |
After reading tdracers informative post this morning, I too was musing: Why is all this attention being given to TCMA.
Of course, when the probable cause is profoundly unclear, our continuing distrust of technical systems comes to the fore .... as sadly, the shadow of MCAS still looms large in our imaginations - Shutdown by crew - Involuntary shutdown by aircraft’s control systems Subjects: None |
| C2H5OH
June 17, 2025, 06:25:00 GMT permalink Post: 11903999 |
On the 767 and 747-400, when you shutdown an engine and the IDG goes offline, there is a momentary 'glitch' in the electrical power system as it reconfigures for the available power source - this is why you see the flight deck displays flicker and return, and the cabin lights momentarily flicker. As a result, most of the avionics boxes 'reset' - this is quick, but it's not instantaneous. This shows up in the FDR data - sometimes as 'no valid data' for a few seconds, or as garbage readings of zero or 'full scale'. Now, looking at the FDR data, it's easy to simply disregard the data, so normally no big deal.
\x85 If there is a fuel cut at high power, the engine spools down incredibly rapidly - a second or two from max power to sub-idle. Assuming the fuel cut wasn't commanded by the flight deck fuel switches, the electrical system won't know it's coming, so it can't reconfigure until after the engine generators drop offline - and you're going to get that power glitch. Nearly every avionics box on the aircraft will reset due to this electrical glitch, and the FDR isn't going to get useful data for a few seconds (and then, only from the stuff that's on the battery bus). This is not only happening to the FDR but to any reciever on the data busses. And likely not only when the engine spools down and power supply switches but also when power busses come offline and bus bar breakers activate or in any severe fault in the electrical system involving large currents, possibly arching shorts. Hence my comments on SISO and input filtering and verification in the closed thread. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FDR Fuel (All) Fuel Cutoff Fuel Cutoff Switches Generators/Alternators |
| C2H5OH
June 17, 2025, 07:48:00 GMT permalink Post: 11904041 |
On the definition of bugs
It doesn\x92t need to be a bug though.
Not specified to cope with and/or not tested for power glitch when transitioning from ground to air mode would be a specification gap that even likely would effect two independent implementations alike. Layman might call something like this \x92bug\x91 but is in fact not. It\x92s a design weakness or specification gap that has not been eliminated in the design process. The complexer systems and algorithms become, the more of these are lingering deep in the shadows. There shall be a sweet spot of complexity (or better simplicity) and undiscovered caveats. In many of today\x92s implementations in many domains we are today beyond that sweet spot. A technocratic can do attitude pushes it even further. Subjects: None |
| C2H5OH
June 17, 2025, 20:33:00 GMT permalink Post: 11904632 |
And again (I made a post somewhere months ago), why on earth doesn't any airport that is say classed as international, have 4k cameras installed.
Look at how many pages have been "were the flaps out on takeoff", and such like, "Ran out of runway" - even (maybe), Engine thrust could be seen, bogey conditions, tire conditions, Could answer a lot of information as to "Was the aircraft in good configuration on Takeoff/Landing', The world has watched hours upon hours of potato cam footage of AI-171 taking off - plus a handheld phone footage taken by a kid, and that's the best a trillion $$ airline industry can do..? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AI171 CVR FDR |
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