Downwash Lesson Plan

A couple of days ago, Tim McAdams posted on his blog, AOPA Hover Power, a couple of examples where pilots have been oblivious to the effect their downwash has on other aircraft. He warns that many pilots either don’t know about the effect their downwash can have on aircraft or personnel on the ground, or they don’t care. The AIM specifically puts the responsibility and discretion on helicopter pilots when judging the effects of downwash on persons and property on the surface (4-3-17(a)(3)). That’s the rationale behind the new lesson plan I just added, Rotor Downwash. (Maria Langer has also written about an incident where another pilot…well, just read her story.)

I trained at a busy school, where there were usually 3 or more R22s on the apron, and occasionally a few R44s, and we were next to a crowded parking area and the fuel pumps. Although the extent of our formal training in managing (and anticipating) the effects of downwash was the one paragraph in the AIM, you learn pretty quickly to keep doors latched, cowlings secured, blades slightly out-of-line with the tail boom, and a hand on your cap when others are arriving or departing. We also frequently had to frequently dodge airplanes that were seemingly oblivious to the recommendations in the AIM.  With the unwitting cooperation of the plank drivers at that airport, I’ve done the experiment and can say that an R22 on approach probably isn’t going to overturn an RV or a 152.

A larger helicopter though, packs a bit of force. I was waiting for a lesson at a small FBO in Oregon a while back. It was an early summer day, with calm winds and clear skies. The operator had just landed a fire contract, and they were practicing long-lining with it on the taxiway. While I was waiting, the mechanic moved a Cessna high-wing out of the hangar to pull out another aircraft, and left it there without tie-downs or chocks. After a half hour, the UH-1 returned to the hangar and went about setting the bucket down so it could land. The rotor diameter on a UH-1 is about 50 fee and they were working a 100-ft longline, so the Cessna was now within the 3-2-1 area (see the new Lesson Plan). There was an oddly calm moment between when the Uh-1 settled into a high-hover and when the downwash hit us. That Cessna was on its way the second the downwash hit us, and made it 20 ft before the mechanic and I stopped it. The force of the downwash from an R22 isn’t much, but the UH-1 laid down an impressive gust. This scene replayed itself almost exactly the same the very next day–the mechanic didn’t chock the plane, the ground crew didn’t prep the area, and the pilot (who worked at the FBO), didn’t make a radio call to have somebody secure the little plane.

Go check out the Rotor Downwash Lesson Plan.