Colorado Aviation Accidents & Incidents

HISTORY OF FLIGHTOn December 5, 2014, about 1428 mountain standard time, a Cirrus SR20 airplane, N407ND, impacted terrain during approach at the Fort Collins-Loveland Municipal Airport (FNL), near Fort Collins, Colorado. The solo student pilot was seriously injured and the aircraft was substantially damaged. The aircraft was registered to and operated by Cirrus LLC under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Day visual meteorological conditions prevailed for the local flight, which departed without a flight plan.

The student pilot stated that he entered the traffic pattern at FNL for a full stop landing on runway 33. He observed a Sikorsky UH-60 helicopter on downwind and delayed his turn to base until the helicopter was on final, abeam his position. While on final, the student pilot adjusted his aim point to land long, as he was concerned with wake turbulence and wanted to land beyond the helicopter's touchdown point. Just prior to landing, he encountered turbulent air, entered into an uncommanded steep left bank, and attempted to go around. The pilot was unable to maintain control and the airplane subsequently impacted terrain and cartwheeled, which resulted in damage to the fuselage and both wings.

An airport surveillance camera at FNL captured the accident airplane approaching the runway about 30 seconds in trail of the departing UH-60 helicopter. METEOROLOGICAL INFORMATIONAt 1435 the weather observation station at FNL reported the following conditions: wind 110 degrees at 3 knots, visibility 10 miles, clear sky, temperature 14 degrees C, dew point 4 degrees C, altimeter setting 30.22 inches of mercury. ADDITIONAL INFORMATIONFAA 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.

The FAA flight test report is included in the public docket for this investigation.

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