Thread: Air India crash

Originally Posted by JDNSW

Just because the swittches were replaced recently does not necessarily mean that they were not lacking the locking mechanism. After all they came from Boeing presumably, and their QC has been a little hit and miss recently.

My feelings also. I also believe the AD should have been mandatory. I know that policing internal flights can be difficult, but international is a different story.

Several people have mentioned that the switches have been changed. How I read it is that the throttle modules have been changed twice. The switches are not part of that module, they are separate, close but not part of it. Boeing are saying that the switches are not a problem, and that is why the FAA issued a SAIB, not an AD.

I was watching a review of the report. It was suggesting the switches were not accidentally turned off. It seems that the switches were shut down per protocol (Engine 1, 2 secs, Engine 2) just after rotate. The other pilot (they're not sure which one) said why did you shut the engines off, the response was that I didn't (commentator suggested the response was as per a child would, rather than one of surprise), 4 secs then rat deployed, then the engines were restarted as per protocol. One motor restarted and began spooling up and began to generate thrust, the other motor restarted but didn't begin generating thrust and then they crashed.

Read the report. The switches were turned off in sequence a maximum of 1 second apart (the sampling rate of those channels in the FDR). The CVR records multiple channels including both pilots headsets separately. I guarantee they know precisely who said what and when.

The preliminary report serves to let the rest of the aviation world know this was not a fault they need to be worried about. That is it.

The rest will have to wait for the final report.

These are 4 pole switches with a pair of redundant data routes and direct wiring to the fuel cut off solenoids / FADECs in the relevant engine. At least 2 of those channels per switch is logged in the FDR so they know damn well there was no mechanical or electronic failure to worry about. They’ll also know from the remainder of the cockpit conversation pretty much what went down (did the PF call for gear up and then the PM cut the fuel instead of raise the gear?, or whatever really went on) so there’ll be a lot of fine correlation (sounds in the cockpit correlating with FDR logs) and background investigation to do before the final report is issued.

in the mean time, it wasn’t a mechanical or maintenance issue so the rest of the world can keep flying.

Claims have been made by a former Inspector General of America's Transportation Department that the fuel cut off switches on a 787 have transitioned from 'run' to 'cut off' on at least one previous occasion.

...The [former] investigation revealed the plane software made the 787 think it was on the ground and the Thrust Control Malfunction Accommodation System cut the fuel to the engines...

As I understand it, the black box logs show both fuel cut off switches transitioned almost simultaneously to 'off' but also show to have later transitioned back to 'run' and to be found physically in the 'run' position at the crash site.

I would have expected if the Thrust Control Malfunction Accommodation System had played a role in this occasion then the black box logs would have shown it.