A group of helicopter pilots and aviation safety professionals have come together to research and share the importance of helicopter wake-turbulence safety with the aviation community.
While long known to exist, the aerodynamic details of helicopter wake turbulence are not fully understood, or documented. Recent accidents and incidents inspired a new push to educate all pilots—both fixed-wing and rotorcraft—about the hazard created for nearby aircraft when helicopters are generating lift near runways and taxiways.
On September 18, Parks and Harwell were present during a fatal accident at Wadsworth Municipal Airport in Ohio involving a Rans S–20 Raven and a Sikorsky S–76 helicopter. According to the NTSB report, “The helicopter was on the approach to runway 2, while the accident airplane had taxied to the end of the runway. Shortly after the helicopter passed the airplane, the airplane taxied onto the runway and started its takeoff roll. Moments later, just after the airplane became airborne, the airplane rolled inverted and impacted the runway. The airplane did not appear to contact the helicopter. A post-crash fire engulfed the airplane.” The report found that the vortices from the rotor blades are violent enough to upset light aircraft.
“This started a whole conversation especially for those of us that are dual rated,” Parks explained, “This is just not a conversation that’s been talked about by anybody, anywhere. We’ve certainly taught wake turbulence, departing landing heavy aircraft…there’s just little to no conversations about this at all…There’s been other research done, mostly with helicopters at a hover…This [report by the FAA] is the only one I’ve found so far that talks about forward flight.”
In their research, Parks and the team have watched multiple videos that captured incidents involving aircraft flying into helicopter wake turbulence. Parks said, “when you see those, it really gets your full and upright attention. I’d never seen them before and when I saw them it just woke us up and here we are as a working group, trying to educate the flying community.”
Parks said much of what is known comes from a 1996 FAA research document, “the only one, so far, that I found [that documented wake turbulence generated by helicopters in] forward flight, and what they discovered in there was pretty amazing.” The report included data from tests performed on wake turbulence from a Bell UH-1, Boeing CH-47 Chinook, Sikorsky CH-53, and a UH-60A Blackhawk. Using the smoke flow visualization technique, they attached smoke to all four helicopters and paired them with an American Champion Super Decathlon and a Beechcraft T–34 Mentor flown by experienced aerobatic pilots. Parks told AOPA that, “in one report, the T–34 experienced a roll-rate up to 60 degree bank in a second.” Another section of the report indicated that on two occasions the Decathlon pilots abandoned a run while flying “in the wake of the CH-53E at a high speed because of an unexpected ‘shudder’ or apparent flapping of the wings.”
Parks went on to share that the FAA has written that to avoid experiencing hazardous wake turbulence (one that induces a roll rate beyond 30 degrees unabated by pilot in a fixed-wing aircraft) one should not operate closer than 3 nautical miles. “Ironically,” Parks continued, describing a night flight with a student practicing instrument approaches in calm wind conditions, with a Eurocopter EC–135 helicopter practicing instrument approaches to the same airport. “I was tracking them on ADS-B, we were 4.2 nautical miles in trail and I was picking up his wake turbulence .... And they were in a descent.”
Park’s referenced a March 5, 2022 incident involving two elderly woman in the United Kingdom who were blown over by a helicopter landing at a hospital while walking on a footpath; one of the pedestrians was killed. “People that don’t know, don’t know, and why would they? They’re walking across a parking lot, why would they think that they’re in danger?”
The group has been presenting at events like HAI’s Heli-Expo as well as virtual presentations to other smaller groups to get the word out. In addition to raising awareness through presentations, the group is also seeking grants to perform additional studies of the effects of helicopter wake turbulence on fixed-wing light aircraft.