The Proton-M mishap on May 16 was caused by a design flaw
Roscosmos, the Russian space agency, announced the results of the investigation on the problem that caused the failure of the mission of the Proton-M rocket on May 16, 2015. The fault was detected in the turbopump rotor of the rocket’s third stage engine which resulted in an instability in the engine that caused the emergency shutdown. According to the investigation, it’s a design flaw and recommendations were issued to correct it.