The United States Navy released their findings today from a command investigation into the crash of Blue Angel #6 during a flight demonstration at Marine Corps Air Station Beaufort on 21 April 2007.

The crash which killed the pilot, LCDR Kevin Davis, occurred after the Blue Angels had completed the Loop Break Cross, a maneuver in which all six aircraft converge on show center from different directions and altitudes. After the aircraft cross show center a choreographed maneuver takes place which allows all the aircraft to rejoin on the leader before their final maneuver, the Pitch Up Break. It was during this rendezvous maneuver that Blue Angel #6 entered a 6.8g turn and slowly lost altitude until impacting some trees and crashing in a sparsely populated area.

According to an opinion stated in the findings, “…although the high rate of turn and sudden onset of positive Gs during the rendezvous maneuver resulted in possible physiological impairment to LCDR Davis, the impairment did not result in either G-LOC [G-induced Loss Of Consciousness] or G-excess illusion. LCDR Davis had fully demonstrated through his Centrifuge training, previous NFDS [Navy Flight Demonstration Squadron] practice and show events and overall flight proficiency an adequate G-tolerance for all demonstration maneuvers. However, the mishap pilot’s failure to perform a proper AGSM [Anti-G Straining Maneuver] resulted in him suffering from possible physiological effects that contributed to his loss of situational awareness of his rate of descent and ultimately a controlled flight into the terrain (CFIT). Had the mishap pilot performed a proper AGSM throughout the maneuver and maintained full situational awareness of his flight attitude, this mishap may have been averted.”

So what is this AGSM? To quote an article from the Air Force Association Magazine, “The AGSM consists of a deep intake of breath, followed by breath-holding and grunting for about three seconds, followed by an explosive exhalation and repetition of the process. This act increases the pressure inside the lungs and chest and, in effect, supercharges the blood pressure on the ‘inlet’ side of the heart. With this technique, a well-trained pilot can raise his blood pressure around four Gs’ worth.” Failure to perform a proper AGSM can lead to grey-out or tunnel vision, followed by black out, and finally loss of consciousness.

Back on 2 Nov 2007, an F-15C from the 110th Fighter Squadron suffered a structural failure and in-flight break-up while performing Basic Fighter Maneuvers. The pilot ejected and survived. The accident resulted in the grounding of all F-15s in the USAF inventory.

Yesterday the USAF released their findings from the accident investigation. They concluded a manufacturing defect in the upper right longeron allowed a fatigue crack to form which resulted in the catastrophic failure of the longeron during a high g maneuver.

The executive summary of the accident investigation board, along with interview transcripts, computer animations, and photographs can be found at http://www.acc.af.mil/aibreports/.