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United States Air Force Aircraft Accident Investigation Board Report, CV-22B, T/N 06-0032, 13 June 2012

CV-22B, T/N 06-0032
13 JUNE 2012

On 13 June 2012 at approximately 2339:55 Zulu (Z) (1839:55 local time), the mishap aircraft (MA), a CV-22B, tail number 06-0032, operated by the 8th Special Operations Squadron, Hurlburt Field, Florida, impacted the ground seven minutes after take-off approximately six miles northwest of Hurlburt Field, just north of gunnery range Alpha 78 (A-78) on the Eglin Range Complex. All five members of the mishap crew sustained injuries requiring medical attention but safely exited the MA shortly after impact. The MA was destroyed upon impact with the loss valued at approximately $78,453,192.00. The MA impacted on military property, damaging several trees prior to striking the ground. Media interest was high and the accident was reported via local, national and international outlets.

The mishap sortie (MS) was a training mission flown as part of a two-ship tactical formation training line. The mishap flight (MF) consisted of the MA and the mishap lead aircraft (MLA), also a CV-22. At 2339:38Z, the MLA began a left 180-degree turn at 30 degrees of bank to bring the MF around to the southeast for the initial firing pass on A-78. During this turn, the MLA descended slightly from 366 to 336 feet mean sea level (MSL). Simultaneously, the Mishap Co-Pilot (MCP) (who was flying the MA throughout the MS) began a brief level right turn at 354 feet MSL, followed immediately by a 30-degree bank, level left turn to maintain separation from the MLA. Although this maneuver never took the MA directly behind the MLA, the MA did cross the MLA’s turning flight path and the MLA’s wake. As the MA crossed the MLA’s flight path, the combination of the MLA’s bank angle and the MA’s bank angle caused the MA’s left proprotor to enter the MLA’s wake.

Once the MA’s left proprotor entered the MLA’s wake, the MA immediately began an uncommanded roll to the left. The Mishap Pilot (MP) placed his hands on the flight controls and both he and the MCP attempted to recover the MA. They were able to stabilize the MA in a wingslevel flight condition but were unable to arrest the descent rate before the MA entered the 80- to 100-foot trees on the range and impacted the ground.

The MP and the MCP believed that they maintained adequate lateral and vertical separation from the MLA’s flight path and therefore that the MA would remain clear of the MLA’s wake. However, data from the MA and MLA flight data recorders revealed that was not the case. The MP’s and the MCP’s misperception was most likely caused by a combination of the MF’s turning flight path and minor changes in the MLA’s altitude.

The Accident Investigation Board President found by clear and convincing evidence that the cause of the mishap was the MP’s and the MCP’s failure to keep the MA clear of the MLA’s wake. When the MA’s left proprotor entered the MLA’s wake, the MA’s left proprotor lost lift, resulting in an uncommanded roll to the left, rapid loss of altitude and impact with the terrain. This error was due to a misperception by both the MP and the MCP of the MA’s location in relation to the MLA’s wake. This misperception caused the MCP, who was at the controls of the MA, to inadvertently fly the MA into the MLA’s wake. This same misperception caused the MP, who was the aircraft commander, to fail to identify the hazardous situation and take appropriate corrective action either by directing the MCP to alter his position or by taking control of the MA and correcting its position to avoid the MLA’s wake.

Under 10 U.S.C. 2254(d), the opinion of the accident investigator as to the cause of, or the factors contributing to, the accident set forth in the accident investigation report, if any, may not be considered as evidence in any civil or criminal proceeding arising from the accident, nor may such information be considered an admission of liability of the United States or by any person referred to in those conclusions or statements.

Full Report [PDF]

Action of Convening Authority [PDF]

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