SpaceX CEO Elon Musk said a methane leak caused the Starship SN11 prototype to explode in midair on March 30. Musk tweeted:
Ascent phase, transition to horizontal & control during free fall were good.
A (relatively) small CH4 leak led to fire on engine 2 & fried part of avionics, causing hard start attempting landing burn in CH4 turbopump.
This is getting fixed 6 ways to Sunday.— Elon Musk (@elonmusk) April 5, 2021
The leak and explosion occurred as the vehicle was beginning preparations to land at SpaceX’s test site at Boca Chica, Texas. It was the fourth failure to land a Starship prototype in as many attempts.
The SN15 Starship is now being prepared for flight. SpaceX elected to skip prototypes SN12 through SN14.