N1774 Crash 6 May 2003 - Bell Shelby Aero 47G2

[tomokc]

A friend was killed almost 10 years ago while administering a check ride in Ardmore, OK. NTSB reports here: http://www.ntsb.gov/aviationquery/index.aspx The cause of the crash was the failure of the throttle linkage.

I'm a fixed wing guy and don't understand helicopters, so I turn to you guys for help in learning what happens when the throttle linkage fails, why they would attempt to RTB instead of immediately landing, and what may have "gone south" on them in the few minutes between their first radio call reporting "throttle linkage problems" and the last radio call instructing "all aircraft to clear the way." They crashed one-half mile from the runway threshold, killing both pilots.

In case you knew him, the DPE was Norm Edwards who was a standardization pilot at US Customs in OKC, based at KPWA.

Thanks.

 

[Retired in SAN]

Hi Tom,
The link you provided took me to the search page for the NTSB. Not the actual event. I would be curious to read it. Hard to say why a throttle linkage issue and extending the flight was the route they chose. Perhaps they were over unfavorable terrain and didn't have the option to land or if the throttle failed on the high side, they may have over spun the main rotor resulting in catastrophic failure. Either way, there wasn't a lot of time to weigh the options. I flew B47's quite a bit in the past although I'm not sure about this specific model. The B47 had no throttle compensation so when the pitch is increased on the main rotor, the pilot needs to anticipate applying more required power to compensate the drag. Not trying to give a lesson on aerodynamics but they may have been at a flatter pitch in the blades, rolled back the power to avoid over speed than requiring more pitch(low RPM), went to increase the power and there was response. The RPM got to low and the rotor stalled. A picture of the site would help tell more of the story. Usually, if it was blade stall, although the aircraft may have been destroyed, a closer look will show the blades, although foiled or wrinkled,will still be attached to the head and in one piece. And I emphasis, all speculation on my part. The 47s have a high inertia rotor head which means they are good for an engine out auto rotation but, if the RPM gets to low, it is harder to recover. Actually had an accident myself in 1988 in a B47 when the stabilizer arm broke off the head. Fortunately we were in a hover and not at altitude. Resulted in minor damage.

Sorry for your loss...