N959DADiamond Aircraft Ind DA20-C1 · 2003

On January 29, 2014, at 1432 mountain standard time, a single engine Diamond DA20-C1 airplane, 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 airplane was departing on a training flight for Pueblo Memorial Airport (KPUB), Pueblo, Colorado. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 91 public use flight.

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 Federal Aviation Administration (FAA) ATC guidance. The controller did not give a wake turbulence advisory, which was not specifically required by FAA ATC guidance.

According to the CFI and student, the airplane entered into 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.

Flight Instructor

The CFI, age 59, held an airline transport pilot certificate with airplane single and multiengine land, airplane instrument ratings. The CFI's flight instructor certificate included airplane single and multiengine land ratings. She had flown 17,047 hours, including 823 hours as a flight instructor in the DA20 and 22 hours of rotary wing hours 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 other helicopter pilots operating in the KFCS pattern at the time of the accident confirmed the departing helicopter was a UH-60.

Student

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. The student progressed normally through the initial flight screening (IFS) syllabus-directed program and had flown about 14 hours in the DA20 previous to the mishap sortie.

The accident airplane was manufactured by Diamond Aircraft Industries, Inc. in 2007 and equipped with a Continental IO-240-B engine. The last annual and 100-hour inspections were completed on December 18, 2013. During the postaccident examination, no anomalies were noted with the engine, flight controls, or other airplane systems. The CFI and student did not observe any anomalies with the airplane.

The weather observation station at KFCS reported the following conditions at 1458: wind 170 degrees at 3 knots, visibility 10 miles, broken clouds at 17,000 feet above ground level (AGL), temperature 5 degrees Celsius (C), dew point negative 8 degrees C, and altimeter setting 29.76.

The left wingtip of the aircraft 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 runway centerline, with the aft fuselage fractured.

When cockpit structure came to rest inverted, the CFI and student found they were unable to egress from the airplane, as only a few inches of space existed between them and the terrain. Because of this, the CFI and student had difficulty accomplishing post-accident actions to minimize the risk of fire. On-scene witnesses and rescue personnel considered 'flipping' the airplane, but re-considered after confirming the airplane's electrical system was de-energized, the fuel system was not compromised, and a lack of injuries of the crewmembers. On-scene personnel waited for airfield crash/fire/rescue, who utilized pneumatic pillows to effectively extract the CFI and student.

Utilizing DA20-C1 performance data, the accident airplane would have reached the midfield location about 25-40 seconds after the ATC takeoff clearance, having climbed to about 150-200 feet AGL. Based on this estimate and ATC audio tapes, the DA-20 trailed the UH-60 about 48-63 seconds at the midfield location.

Doss Aviation Inc., owner of the accident airplane and employer of the CFI, has operated the IFS program under contract with the USAF since 2006. In September 2008, a Doss Aviation DA20 encountered the wake turbulence of a C-130 during final approach to Doss Aviation's home airfield. Flying 56 to 62 seconds behind the C-130's flight path, the crew was unable to recover from the effects of the wake turbulence vortices. Following that accident, Doss Aviation had placed additional emphasis on the inherent risks of the DA20's very lightweight design and the avoidance of wake turbulence.

In the months leading up to this accident, an Army Combat Aviation Brigade (CAB) had started to arrive at KFCS. About three weeks prior to the accident, increased exposure to helicopters was briefed as a safety topic during a Doss Aviation continuation training (CT) meeting. The briefing focused on risks associated with rotorwash/wake turbulence and the different types of helicopters expected to be located at KFCS as part of the CAB. The briefing provided 'rules-of-thumb, to include a 2 minute wake turbulence spacing in trail from helicopters, although Doss did not make this mandatory. The accident CFI attended the CT briefing on helicopter hazards.

At the time of the accident, a warning in the IFS In-Flight Guide for operations at KFCS read as follows: "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. Consider wind direction to predict wake vortex movement, and use greater than 500 feet separation if required. Make an early go-around decision when required to avoid wake turbulence."

Following the accident, Doss Aviation released guidance requiring their pilots to maintain a wake turbulence separation of 2 minutes behind 'small plus' aircraft, which included UH-60 and AH-64 helicopters, two of the primary aircraft assigned to the CAB. Also since the accident, the USAF operations group overseeing the IFS program regenerated the Southern Colorado (SOCO) Front Range Airspace Working Group (FRAWG), which had been more active when IFS was initially stood up, but had waned recently. The charter of the FRAWG, comprised of SOCO military/civilian flying and ATC organizations, is to reduce congestion risks and optimize efficient use of the available airspace.

FAA Flight Test Report

In February 1996, the Federal Aviation Administration (FAA) Technical Center released a flight test report (DOT/FAA/CT-94/117) on the hazards of rotorcraft wake vortices in forward flight. The flight test utilized a laser Doppler velocimeter (LDV) to measure helicopter wake vortices. Four helicopters, with weights ranging from 7,600 to 70,000 pounds, were utilized as the wake vortex generating aircraft. The maximum duration for vortex life, as measured by the LDV, was 75 seconds for the UH-60. The FAA flight test report made the following conclusions:

--Medium weight helicopters, such as the S-76A and UH-1….can leave active, potentially hazardous vortices for up to 90 seconds. Separations for small aircraft behind these rotorcraft should therefore be in the 90-second range.

--Larger helicopters, such as the CH-47D and CH-53E ….were observed to have longer hazard times. A 120-second separation should be adequate for operations behind these rotorcraft.

--Information on the wake vortex hazard behind these rotorcraft, including delineation by class, should be included in the Airman's Information Manual and the Wake Vortex Advisory Circular.

FAA ATC guidance

Current FAA ATC guidance published in FAA order 7110.65M places all helicopters in the same wake turbulence category as small aircraft. Based on this, FAA ATC wake turbulence guidance does not require an in-trail distance or timing separation for a small airplane following a helicopter, nor is a controller specifically required to give a wake turbulence advisory for a small airplane following a helicopter. Current FAA ATC guidance states: "issue cautionary information to any aircraft if in your opinion, wake turbulence may have an adverse effect on it".

FAA Pilot guidance

Similarly for FAA pilot guidance, the current FAA airman information manual (AIM) and advisory circular (AC) 90-23G on aircraft wake turbulence do not recommend an in-trail distance or timing separation for an airplane following a helicopter. The AC contains a general wake turbulence statement: "pilots should avoid helicopter vortices since helicopter forward flight airspeeds are often very low, which generate strong wake turbulence."