UH-60 Rotor wash (Vortices) flip a Cirrus Aircraft.

[Cliff_Chambliss]

Very interesting clip.   Notice how long the disturbed air remained over the runway.  Typically I teach students to stay at least 5 times the rotor diameter away from helicopters and to also stay upwind.  However in a light wind condition the vortices can remain on the runway for as long as 5 minutes.

So, Safety Note:  The next time that pesky tower controller tells you to wait 3 to 5 minutes for wake turbulence you may want to think again before you respond with "waive wake turbulence" just to speed up you takeoff time.

https://www.youtube.com/watch?v=l8EwvDTJeNs

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On December 5, 2014, about 1435 central 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 and attempted to go around. The airplane subsequently impacted terrain and cartwheeled, which resulted in damage to the fuselage and wings.

An airport surveillance camera at FNL captured the accident airplane approaching the runway about 30 seconds in trail of the UH-60 helicopter.

At 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 Celsius (C), dew point 4 degrees C, altimeter setting 30.22 inches of mercury.

[LTCinSWR]

That hurt just watching it. A very fortunate student pilot -that could have ended very badly. The bigger the rotor, the longer the turbulence.

I do have a couple questions. Could the vortices have been enhanced by the helicopter in the lower left of the video doing its run-up? Would that or could that have prolonged the ground effect with the low winds (wind 110 degrees at 3 knots)?

[Check Pilot/Tow Pilot]

That hurt just watching it. A very fortunate student pilot -that could have ended very badly. The bigger the rotor, the longer the turbulence.

I do have a couple questions. Could the vortices have been enhanced by the helicopter in the lower left of the video doing its run-up? Would that or could that have prolonged the ground effect with the low winds (wind 110 degrees at 3 knots)?

Interesting discussion on Reddit:

http://www.reddit.com/r/flying/comments/2ueyqm/blackhawk_vortices_flip_cirrus_watch_out_for_wake/

[LTCinSWR]

Interesting discussion on Reddit:

http://www.reddit.com/r/flying/comments/2ueyqm/blackhawk_vortices_flip_cirrus_watch_out_for_wake/

Lots of potential contributing factors mentioned. Any incident has a lot of moving parts (figuratively and literally).

[Live2Learn]

I read several of the posts on the reddit blog supposedly inhabited by Blackhawk pilots.  The consensus of that group was "no way" could the video depict a downwash/wake turbulence problem.  I think those 'pilots' were afflicted by severe myopia and hubris.  I've not experienced downwash in the air, but have had clueless rotor wing pilots air taxi near my aircraft while it was on the ground.  Rotor induced turbulence is real and vicious!

The Pilot's Handbook of Aeronautical Knowledge at page 4-8 is pretty clear that rotor wash is a big deal.  "A hovering helicopter generates a down wash from its main rotor(s) similar to the vortices of an airplane. Pilots of small aircraft should avoid a hovering helicopter by at least three rotor disc diameters to avoid the effects of this down wash. In forward flight this energy is transformed into a pair of strong, high-speed trailing vortices similar to wing-tip vortices of larger fixed-wing aircraft. Helicopter vortices should be avoided because helicopter forward flight airspeeds are often very slow and can generate exceptionally strong wake turbulence."  The Blackhawk is shown flying down the runway within 20-30 seconds of when the Cirrus arrived, so the entire runway was likely affected by residual rotor wash vortices.  Under those circumstances I think the best course for the Cirrus pilot was a 'go around' to let the air settle.

[LTCinSWR]

I think those 'pilots' were afflicted by severe myopia and hubris.  I've not experienced downwash in the air, but have had clueless rotor wing pilots air taxi near my aircraft while it was on the ground.  Rotor induced turbulence is real and vicious!

All people have to do is look at a few video of Blackhawks landing or taking off in 'the sandbox' (both from within the aircraft and at a distance) to make your point about myopia and hubris.

[Live2Learn]

This image http://www.efluids.com/efluids/gallery/gallery_pages/HW016/text.jsp illustrates vortex production from a helicopter in forward flight.  I expect a helicopter in ground effect would create more pronounced (severe!) turbulence.  The NASA image of a Blackhawk's wake while in forward flight at altitude is even more dramatic!