With 260 casualties and only one surviving passenger, the Air India 171 crash is one of the deadliest aviation incidents in recent history — and so far it’s proving to be one of the most frustratingly opaque.

Sumeet Sabharwal, 56, was the captain on the flight, while Clive Kunder, 32, was the co-pilot who was flying the plane. Together, the two pilots had more than 19,000 hours of flight experience - nearly half of it on the Boeing 787. Both had passed all pre-flight health checks before the crash.

Air India said on Tuesday it has completed precautionary inspections of the fuel control switch locking mechanism on all its Boeing 787 and 737 aircraft, with no issues detected.