Originally Posted by Algol
But no. Now we discover that if the GPS doesn't agree with the INS's it will effectively vote itself out of the system, and the only warning you'll get is one single chime after it has thought about it for ten minutes (or more)! Incredible.
I read somewhere that this is the same for 747-400s (at least the part about the GPS being voted out).
According to the report, the aircraft in the incident did throw up a warning about position mismatch during the preflight, but the captain forced through it. i.e. the basic position comparison (which looks at both latitude and longitude).
Originally Posted by RAT 5
So their technical knowledge seems to have been lacking. Firstly the attempt to realign in the air, and then how to recover sufficient display data to allow a safe return to Sydney.
That was my initial impression, too, but if you read the report, they did eventually follow the QRH to get the aircraft into basic attitude mode. With limited visibility for a return to Sydney, basic attitude mode may have been insufficient to meet regulatory requirements/airline SOPs (?)