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.