Friday, July 5, 2013

Thoughts On A Recent Accident

Recently it was reported that a South Carolina businessman on a recertification flight in a Rockwell Turbo Commander 690B crashed over McClellanville, SC. Two people were killed, the 44 y.o. pilot and the 69 y.o. instructor. They had taken off from John’s island airport and were to operate between 13000 and 15000 feet as cleared by ATC. Supposedly the pilot-owner had been flying this plane for three years. Credentials of the instructor are unknown.

The purpose of the flight as stated above, was to recertify the pilot, presumably for insurance reasons. To comply, generally a set of flight skills are examined. These would typically include: take-off and landings, air work such as steep turns, slow flight etc. and of course instrument flight under simulated low visibility conditions. The other important area of consideration is putting the pilot through simulated engine out procedures. This normally is done by retarding power to flight idle on one engine, usually the so called critical engine (usually the left hand engine on most twins). Finally, the approach to a stall with one engine idled is tested, likely also with the pilot under simulated IFR conditions (pilot hooded). This latter flight test just may be the cause of the recent crash.

Now it has been a few years since I went through a similar procedure. It was when I flew part-time charters for a fixed base operator (FBO) in Burlington, VT. Every six months it was necessary to obtain a check ride with a certified instructor in order for me to legally fly charters. These charter flights included both passengers and/or freight.

Typically the check rides consisted of a variety of maneuvers including slow flight and this key: slow flight approach to a stall with one engine “out”. With an “out” engine being simulated by retarding the throttle of one of the engines, usually the “critical” one (see above). Before entering into this exercise, the correct procedure for carrying it out was clearly discussed with the instructor. The hazard to this maneuver was this*: if while slowing the plane by bringing its nose up, the plane was allowed to stall, a violent falling off towards the “dead” engine most likely would occur. This almost certainly would progress into a flat spin with possible aircraft inversion. If that were to happen, it most likely would be unrecoverable. The goal of the exercise was early recognition of an impending stall. Once the warning of a stall is received as for example by noting some slight vibration in the control yoke, a prompt push of the control yoke is done to start the plane down immediately. Some of the more sophisticated aircraft have various indicators of stall, including: lights, buzzers and other type annunciators. The reason for all of this is that a stall in a complex plane like the above twin has a reasonable likelihood of being a fatal event. (See NTSB report referenced below)

When I was practicing this on my check ride in a B-58 Baron, all went well. I brought the nose of the airplane up until the first indication of an imminent stall, and then quickly shoved the nose down, allowing the plane to regain a safe flying speed. The next week however, another pilot was undergoing the same series of maneuvers, including the approach to stall with one engine ”out”. This time however, the pilot waited too long to push the nose down and the plane entered the stall with the awful result discussed above. The plane, the same one I had flown, entered a flat spin and descended rapidly towards the waiting rough terrain. Fortunately the instructor pilot was a National Guard F-16 instructor pilot and was able to stop the spin just before the plane struck the ground. There were serious injuries, a destroyed aircraft but no deaths.
This scenario is what I think may have occurred over McClellanville.

*NTSB Aircraft Accident Report, North American Rockwell Turbo Commander 690, Wellsburg, West Virginia, 8/14/72 NTSB-AAR73-5, A-73-8 thru 10

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