Jan 2, 2014 12:58 PM by Q2 News

Air Force releases cause of B1 crash in Montana

A displaced fold-down baffle in the left fairing of B-1B Lancer led to a fuel leak and a series of explosions prior to it crashing near Broadus, according to a report on the incident from the U.S. Air Force.

Four crew members ejected safely and suffered non-life-threatening injuries in the incident that happened last Aug. 19. The aircraft, valued at about $317.7 million, was destroyed.

There were no injuries to civilians, and damage to private property consisted of burned pasture land.

Both aircraft and crew were assigned to the 34th Bomb Squadron, 28th Bomb Wing, Ellsworth Air Force Base, South Dakota. When the accident occurred, the pilots were participating in a post-deployment training flight.

According to an Air Combat Command Accident Investigation Board report released recently, during the flight the pilot leveled the aircraft off at about 20,000 feet. While descending to about 10,000 feet, he swept the wings from the forward to the aft position. The wings of the B-1B move from a forward position to an aft position to increase the aircraft's performance at different speeds.

During the sweep, the aircraft developed an undetectable fuel leak in the main fuel line. About 7,000 pounds of fuel leaked into the aircraft.

The fuel eventually contacted exposed portions of a hot duct, ignited, and caused an explosion that separated the left overwing fairing from the aircraft.

Ignited fuel streamed from the exposed left overwing fairing cavity, heated one of the aircraft's fuel tanks, and ignited the fuel vapors inside the tank. This detonation spread through the fuel venting system that connects the fuel tanks in the aircraft, and resulted in a cascade of detonations that caused a complete loss of power to the crew compartment, the report states.

At some time prior to pilot's initiation of the wing sweep, the left fold-down baffle became detached at one or more points, preventing it from folding as the wing swept aft, the report states. Because the baffle was detached, the wing pushed the baffle into the overwing fairing cavity where the tapered edge of the baffle cut into the main fuel line.

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    B1 crash site
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