Pilots’ actions after the bird strike are an early focus of the investigation, according to people familiar with the probe.

Jet engines are incredibly powerful, complex pieces of precision engineering, running at the finest of tolerances; bird strikes can push these tolerances to the limits. When a bird is ingested into an engine, the first thing the unfortunate creature will meet is the fan blades, typically rotating between 2200 rpm and 4500 rpm.

The first report on last month’s Jeju Air crash in South Korea has confirmed bird strikes in the plane’s engines, though officials haven’t determined the cause of the accident that killed all but two of the 181 people on board.