According to air traffic control (ATC) audio recordings, a tower controller cleared the Diamond DA20 for takeoff from the airport in Fort Carson, Colo., about 23 seconds after a UH-60 helicopter was cleared for takeoff from a midfield location.
The tower controller ensured that a runway separation standard of 3,000 feet was present and did not give a wake turbulence advisory.
The flight instructor reported she was aware of the helicopter’s takeoff and that she perceived adequate separation from the helicopter. The flight instructor incorrectly identified the helicopter as a Bell UH-1, which weighs less than the UH-60.
Shortly after takeoff, the plane encountered the wake vortex of the helicopter and entered a steep left bank. The flight instructor attempted to counteract the left roll with full right aileron inputs, but she was unable to maintain control. The plane hit terrain near midfield and came to rest inverted.
A review of ATC audio recordings and airplane performance data revealed that the airplane trailed the helicopter by about 48 to 63 seconds at the midfield location and was about 150 to 200 feet above ground level when it encountered the helicopter’s wake vortex.
Current FAA ATC guidance does not require specific wake turbulence separation criteria for a small airplane following a helicopter nor does it require a controller to give a wake turbulence advisory for a small airplane following a helicopter.
Current FAA pilot guidance, including the Airman’s Information Manual and an advisory circular on aircraft wake turbulence, also do not recommend separation criteria for a small airplane following a helicopter.
The NTSB determined the probable cause as the flight instructor’s loss of control after takeoff following a wake turbulence encounter from a preceding helicopter. Contributing to the accident were the flight instructor’s misidentification of the helicopter type and a lack of FAA wake turbulence separation criteria for a small airplane following a helicopter.
NTSB Identification: CEN14TA126
This January 2014 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.