When landing, you have essentially to be above the preceding traffic’s path along the whole glideslope to stay out of its wake.
By only extending his downwind and landing long he had to cross the glide path at some point.
Three minutes. Rotor wash is at least as hazardous as fixed wing wake turbulence. It’s not much different from wind shear, if you use that. Rotor wash can change your airspeed in a heartbeat.
The comments on this accident are weird, as they seemingly contradict each other. In the article (and IMO the video) it says/shows the Blackhawk departing. However, the Cirrus pilot reports that he saw the Blackhawk on downwind:
The student told investigators he had spotted the Black Hawk while the military helicopter was on downwind
So – what was the Blackhawk doing? T&Gs ?? Low approach / pass? Or does the student mean to say he saw the helo while he himself was on downwind?
In any case, lesson learned: give helos a wide berth and some time!
Slight thread drift; This is a nice video of vortices generated by airliners:
Do vortices from helicopters behave in a different way from fixed wing vortices? Quote
Yes and no.
Yes, in that in “cruise” flight, a helicopter rotor disc is pretty well the same as a wing, It’ll shed vorticies about as a wing for a similar weight aircraft will. They could be a bit more or less intense, based upon disc loading, just as they could be with different wing loading, and flap use.
However, unlike a wing, rotor lift does not stall as airspeed slows, helicopters hover instead. So, about the airspeed where the airplane wing would be stalling, the lift produced by the rotor changes from acting mostly as a “solid” disc, to now being the fan we imagine. This speed is called translation speed. This speed is subtly noticeable to the pilot in a change in the effect of the flight controls. It is very noticeable to the air around as a change from a somewhat downward only column of air in the hover (or very slow speeds in any direction) to the generation of vorticies as fixed wing pilots think of them. Therefore, it is quite possible for there to be no vorticies around a helicopter hovering above a runway, and they suddenly start, at the point where the helicopter reaches around 30 knots forward speed.
This is the same as the vorticies from a large jet simply stopping shortly past the touchdown point. All the spoilers come up, and much of the lift ends, so do the vorticies.
Unfortunately neither PPL or IR training for fixed wing make much mention (if any) of helicopter vortex avoidance — only avoidance of vortices from other fixed wing aircraft.Quote
It’s in every pilot’s interest to get to know this stuff. Interestingly, on the 30 question PPLH exam I took to get a PPLH having already a PPLA, there were three questions on wake turbulence avoidance. If in doubt, do not get within three minutes flying behind anything heavier than your plane.
It seems to be more common on some mixed military/civil airports in the US to operate fixed wing aircraft close to helicopters. Maybe familiarity and all that…
Having started up the 172 on the FBO ramp at Chicago’s Midway Field, a Blackhawk helicopter lifted into the hover right in my direction of taxi and maybe 100’ away. A chap in the open doorway gestured toward me and beckoned for me to move forward. Military and civil use different frequencies at Midway and I was still on the ramp, not yet having called for taxi, so there was no obvious way to communicate with the helicopter pilot. Anyway I was struggling about how to explain to ATC at this very busy place about wanting taxi, but unable due helicopter or something. (On reflection, with the benefit of hindsight, I could have called the FBO to ask if they knew what was going on I suppose).
So I just waited, while the chap’s gesticulations continued. Eventually, after what seemed like 5 mins or so, the helicopter settled down again and I taxied past. The doorman gave me a hands in the air gesture, as much as to say “Chicken”. But I didn’t feel chicken. Fresh in my mind was the account of what had happened to the poor chap in another 172 at Newquay, who was burnt alive after an (alleged) encounter with a hovering helicopter.
When the video starts It looks like it is accelerating at low level to a safe climb-out speed, which is normal.
We cannot see whether it previously transitioned to a hover (lots of vortices, all around one spot on a low-wind day), or just went around.
