Any airline disaster demands explanation, but the Ethiopian Airlines crash on Sunday — the second in less than five months by the same new model of plane — raises more than the usual questions and fears.

Shortly after the Boeing 737 Max 8 took off from Addis Ababa, the capital of Ethiopia, bound for Nairobi, Kenya, the pilot sent a distress call and received permission to return to the airport. Six minutes after takeoff, the jet plunged to earth, killing all 157 people aboard.

Here is a look at what we know about the disaster — and what we still don’t.

[Read our latest updates on the Ethiopian Airlines crash.]

What caused the crash?

It is much too soon to say why the plane went down, or to rule out possibilities like pilot error, mechanical breakdown, maintenance problems or terrorism.