Azerbaijan held a day of mourning on Thursday for the dozens of victims of an airliner crash in Kazakhstan, as questions were being asked over the cause of the disaster.

Of 62 passengers and five crew members on board the Azerbaijan Airlines flight, 29 survived, according to Kazakhstan’s authorities.

The crash of an Azerbaijani airliner in Kazakhstan has killed 38 of 67 people on board. Azerbaijan Airlines’ Embraer 190 was en route from Azerbaijani capital Baku to the Russian city of Grozny in the North Caucasus on Wednesday when it was diverted for reasons that aren’t fully clear yet.