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.

Mobile phone footage circulating online appeared to show the Azerbaijani Airlines plane making a steep descent before slamming into the ground in a fireball in western Kazakhstan.