A displaced fold-down baffle in the left overwing fairing of a B-1B Lancer led to a fuel leak and a series of detonations that disabled the aircraft prior to it crashing Aug. 19 near Broadus, Mont., according to an Air Combat Command Accident Investigation Board report released Monday.
The four crewmembers ejected safely and sustained non-life-threatening injuries. The aircraft was destroyed, with the government loss valued at approximately $317.7 million. There were no injuries to civilians, and damage to private property consisted of burnt 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 allowing them to become current on combat-mission readiness training items.
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 a training mission, the pilot leveled the aircraft off at an altitude of roughly 20,000 feet. While on a descent to 10,000 feet, he swept the wings from the forward to the aft position. During the sweep, the aircraft developed an undetectable fuel leak in the main fuel line. Unbeknownst to the crew, approximately 7,000 pounds of fuel leaked into the aircraft during the training mission.
Eventually, the fuel contacted exposed portions of the hot precooler 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 and permanent loss of power to the crew compartment.
According to the results of the investigation, 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. Because the baffle was detached, the wing pushed the baffle into the overwing fairing cavity where the tapered edge of the baffle cut a v-shaped hole in the main fuel line.
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