A Russian Boeing 737 crashed Sunday morning in the city of Kazan, killing all 50 people on board, officials said. The Tatarstan Airlines flight took off from Moscow, and crashed about 450 miles east of there. It’s unclear what caused the crash. Reports said the plane lost altitude as it made a second landing attempt, and then allegedly crashed and caught fire at 7:20 p.m. There were 44 passengers and six crew members on board, a spokesman for the Emergencies Ministry said.