Rapid City, SD -

An Ellsworth Air Force Base leader says the crash of a B-1 bomber last August during a training exercise over southeastern Montana was an anomaly and not indicative of a bigger problem in the 30-year-old bomber fleet.

An Air Force report released earlier this week says the crash was caused by a mechanical malfunction that started a fuel leak. About 7,000 pounds of fuel leaked into the aircraft and was ignited by hot ductwork, leading to a series of detonations in the plane.

The four crew members safely ejected. No one on the ground was hurt.

Ellsworth 28th Bomb Wing Vice Commander Col. Gentry Boswell tells the Rapid City Journal that the B-1 has a proven track record, and the mechanical failure was not tied to the plane's age.