Originally Posted by
Centaurus
If I recall, a Lion Air Indonesia B737 went into a gradual spiral at night with devastating consequences. Seems the crew were having difficulties with one of the to IRS. in fact there were many reported snags on that IRS previously.
Hi Centaurus,
I can't find a Lion Air incident matching that profile - are you sure you're not thinking of Adam Air 574?
Admittedly it wasn't at night, but the weather was pretty rotten. The Captain was experienced, but new to the airline. They had INS issues as you say, exacerbated by the fact that the aircraft tended to roll to the right when AP was disengaged. They attempted to reset the two INS units without realising that this should be done on the ground, or at the very least with wings held level (as a last resort only). The INS therefore reset itself with a significant tendency to roll right and the rest is history.
The issue was in part incorrect problem-solving on the part of the crew, but underlying that was a significant can of worms regarding company maintenance. One of the leading theories was that the airframe itself was damaged, leading to a tendency to roll to the right, but as soon as AP was engaged, the automation compensated. The Captain noticed this when AP disconnected, hence his desire to re-engage in order to troubleshoot. He incorrectly assumed that the right roll tendency was a fault within the automation, and I have to wonder how many other pilots would have done the same?