History of Flight
On January 29, 2014, at 1432 mountain standard time, a single-engine Diamond DA20-C1 airplane, registration N959DA, was substantially damaged after impact with terrain at Butts Army Airfield (KFCS), Fort Carson, Colorado. The flight instructor (CFI) and student suffered minor injuries. The airplane was owned by Doss Aviation Incorporated and operated under contract for the United States Air Force (USAF). The flight was a training departure for Pueblo Memorial Airport (KPUB), Pueblo, Colorado. Visual meteorological conditions prevailed.
According to air traffic control (ATC) audio recordings, the KFCS tower controller cleared the DA20 for takeoff from the approach end of Runway 13 about 23 seconds after a Sikorsky UH-60 helicopter was cleared for takeoff from a midfield location. The tower controller ensured a runway separation standard of 3,000 feet was present, as required by FAA ATC guidance. The controller did not give a wake turbulence advisory, which was not specifically required by FAA ATC guidance.
The CFI and student reported that the airplane entered a steep left bank soon after liftoff. The flight instructor attempted to counteract the left roll with full right aileron inputs but was unable to maintain control. The airplane impacted terrain near midfield and came to rest inverted.
Personnel Information
The CFI, age 59, held an airline transport pilot certificate with airplane single- and multiengine land ratings and a flight instructor certificate with single- and multiengine land ratings. She had accumulated 17,047 flight hours, including 823 hours as a flight instructor in the DA20 and 22 hours of rotary-wing flight time early in her career. The CFI stated with certainty that she perceived the preceding helicopter to be a Bell UH-1, which weighs less than a UH-60. Interviews with tower controllers and helicopter pilots confirmed the departing helicopter was a UH-60.
The student was a USAF officer with limited flying experience. His previous flight time included about 15 hours in the T-53A (a Cirrus SR-20 variant) at the USAF Academy's Powered Flight Program. He had flown about 14 hours in the DA20 prior to the mishap sortie.
Aircraft Information
The accident airplane was manufactured by Diamond Aircraft Industries in 2007 and equipped with a Continental IO-240-B engine. The last annual and 100-hour inspections were completed on December 18, 2013. Postaccident examination revealed no anomalies with the engine, flight controls, or other airplane systems. The CFI and student reported no anomalies before the event.
Meteorological Information
The weather observation station at KFCS reported at 1458: wind 170 degrees at 3 knots, visibility 10 miles, broken clouds at 17,000 feet above ground level, temperature 5 degrees Celsius, dew point -8 degrees Celsius, and altimeter setting 29.76 inches of mercury.
Wreckage and Impact Information
The left wingtip struck the terrain 118 feet left of the runway centerline. The airplane cartwheeled and the main cockpit/fuselage came to rest inverted 2,511 feet from the approach end and 285 feet left of the runway centerline, with the aft fuselage fractured.
Survival Aspects
When the cockpit structure came to rest inverted, the CFI and student found they were unable to egress due to only a few inches of space between them and the terrain. This difficulty impeded post-accident actions to minimize fire risk. On-scene witnesses and rescue personnel considered flipping the airplane but reconsidered after confirming the electrical system was de-energized, the fuel system was not compromised, and the crew was uninjured. Rescue personnel used pneumatic pillows to extract the CFI and student.
Tests and Research Information
Using DA20-C1 performance data, the accident airplane would have reached the midfield location about 25–40 seconds after ATC takeoff clearance, at an altitude of about 150–200 feet AGL. Based on this estimate and ATC audio tapes, the DA20 trailed the UH-60 by about 48–63 seconds at the midfield location.
Organizational and Management Information
Doss Aviation has operated the Initial Flight Screening (IFS) program under contract with the USAF since 2006. In September 2008, a Doss Aviation DA20 encountered wake turbulence from a C-130 during final approach, and the crew was unable to recover. After that accident, Doss emphasized the risks of the DA20's lightweight design and wake turbulence avoidance.
About three weeks before this accident, an Army Combat Aviation Brigade began arriving at KFCS. A Doss Aviation continuation training meeting briefed helicopter hazards, including a 2-minute wake turbulence spacing rule of thumb from helicopters, though not mandatory. The accident CFI attended that briefing. The IFS In-Flight Guide included a warning: "Use extreme caution operating in the vicinity of helicopters. Do not takeoff or land with helicopters hovering or taxiing within 500 feet of the runway."
Following the accident, Doss Aviation released guidance requiring their pilots to maintain a wake turbulence separation of 2 minutes behind 'small plus' aircraft, including UH-60 and AH-64 helicopters. The USAF operations group also regenerated the Southern Colorado Front Range Airspace Working Group to reduce congestion risks.
Additional Information
A 1996 FAA flight test report measured helicopter wake vortices, showing a maximum vortex life of 75 seconds for the UH-60. The report concluded that medium-weight helicopters can leave hazardous vortices for up to 90 seconds, and larger helicopters require 120-second separation. Current FAA ATC guidance places all helicopters in the same wake turbulence category as small aircraft, not requiring specific in-trail separation for a small airplane following a helicopter. The FAA Airman's Information Manual and Advisory Circular 90-23G also do not recommend specific separation timing but note that pilots should avoid helicopter vortices due to strong wake turbulence.