An investigation into the loss of two Royal Netherlands Air Force (RNLF) Boeing CH-47D Chinook transport helicopters in Afghanistan in 2005 has identified pilot error and a lack of experience in operating in difficult terrain as the main causes in both non-fatal accidents.
On 27 July 2005, the crew of Chinook D-105 were flying a night mission as part of a two-ship formation to resupply Special Forces personnel, but were forced to abandon their initial landing attempt when the lead aircraft created brown-out conditions.
The second crash followed an in-flight route change over mountains
During their second attempt, the pilots failed to notice a left-hand drift, which caused the aircraft to roll over when it touched down. Although the crew evacuated safely, the aircraft and its flight data recorder were destroyed in the resulting fire.
Dutch military aviation authority the MAA says contributing factors included the need to conduct a difficult landing while carrying a heavy payload and using night-vision goggles, plus psychological stress that resulted in poor crew communication.
Procedural shortcomings were also highlighted in its report, which says an in-flight decision to use one rather than two landing zones meant landing beacons were placed too far apart, and that D-105's pilots did not follow the procedure for an aborted landing after misjudging the position of the first Chinook.
The crew also had only limited experience in flying under such conditions, it says - a concern that the pilots had raised with their commanding officer four months before the crash.
Chinook D-104 was lost on 31 October 2005 while carrying personnel and equipment from Mazar-e-Sharif to Kandahar airfield. During the flight, its captain decided to change the route, shortening the sortie time by 30-45min, but requiring the aircraft to fly along a dead-end valley before rising over a high mountain ridge.
However, the required angle of climb exceeded the Chinook's capabilities, forcing the crew to perform a 180° turn, in the course of which they lost control of the aircraft. It subsequently crashed, injuring one person.
The MAA says the pilots failed to give enough attention to the flightplan to judge the consequences of the route change, and that assumptions were not properly validated using available data. The pilots also did not act properly on encountering less lift than anticipated, and should have planned an escape route which allowed enough time to turn around.
However, the report says technical factors also contributed to the accident, as a temperature-related limitation degraded engine power and caused the instruments to display the wrong reading for maximum available power, giving the crew the impression that they had sufficient margin to cross the ridge.
All valuable parts were stripped from the heavily damaged aircraft before it was destroyed.