Ford was born at the Swedish Covenant Hospital in Chicago, Illinois to Christopher Ford (born John William Ford), an advertising executive and former actor, and Dorothy (nee Nidelman), a former radio actress. His father is Irish and his mother is Jewish. A younger brother, Terence, was born in 1945. Ford's paternal grandparents, John Fitzgerald Ford and Florence Veronica Niehaus, were of Irish Catholic and German descent, respectively.

On October 23, 1999, Harrison Ford was involved in the crash of a Bell 206L4 LongRanger helicopter (N36R). The NTSB accident report states that Ford was piloting the aircraft over the Lake Piru riverbed near Santa Clarita, California, on a routine training flight. While making his second attempt at an autorotation with powered recovery, Ford allowed the aircraft's altitude to drop to 150-200 feet before beginning power-up. The aircraft was unable to recover power before hitting the ground. The aircraft landed hard and began skidding forward in the loose gravel before one of its skids struck a partially embedded log, flipping the aircraft onto its side. Neither Ford nor the instructor pilot suffered any injuries, though the helicopter was seriously damaged. When asked about the incident by fellow pilot James Lipton in an interview on the TV show Inside the Actor's Studio, Ford replied, "I broke it."  On March 5, 2015, Ford's plane, believed to be a Ryan PT-22 Recruit, made an emergency landing on the Penmar Golf Course in Venice, California. Ford had radioed in to report that the plane had experienced engine failure. He was taken to Ronald Reagan UCLA Medical Center, where he was reported to be in fair to moderate condition. Ford suffered a broken pelvis and broken ankle during the accident, as well as other injuries.  On February 13, 2017, Ford landed an Aviat Husky at John Wayne Airport on the taxiway left of runway 20L. A Boeing 737 was holding short of the runway on the taxiway when Ford overflew them.

Using a quote from the above article, answer the following question: What was the cause?
The aircraft was unable to recover power before hitting the ground.