Conversation so far:
What types of incidents have happened to Harrison Ford?
Harrison Ford has had several incidents while piloting aircraft
has Harrison Ford had any accidents or incidents that are noteworthy?
On October 23, 1999, Harrison Ford was involved in the crash of a Bell 206L4 LongRanger helicopter. The helicopter hit the ground and flipped over onto its side
when was the accident when Harrison Ford suffered a broken pelvis and ankle?
On March 5, 2015 Ford made an emergency landing and suffered a broken pelvis and ankle

Question: what caused the accident?
Self-contained rewrite: What caused Harrison Ford's accident?