Plane & Pilot
Tuesday, April 1, 2014

More Alerts For GA Pilots

The NTSB highlights five more areas it believes need attention

Both the pilot and passenger were killed, and the investigators said that a review of the autopsy results and impact damage to the wreckage indicated that had the occupants been restrained by shoulder harnesses, their chances of survival would have been a lot better. The airplane wasn't manufactured with shoulder harnesses, though there was the opportunity to do a subsequent installation. In June 1985, the manufacturer issued a mandatory Service Bulletin announcing the availability of shoulder harness kits for the model involved in the accident and many others. In September 1990, the Service Bulletin was revised to offer an incentive to owners who upgraded their airplanes with the shoulder harness kits prior to October 31, 1992.

The NTSB made note of an FAA publication discussing occupant protection for small airplanes (FAA document #AM-400-90/2). In it, the FAA reports that seat belts alone will only protect the occupant in very minor impacts, and that using shoulder harnesses in small aircraft would reduce injuries by 88% and fatalities by 20%.

Another accident cited by the NTSB in the Safety Alert on restraints involved a crop sprayer. The Piper PA-36-285 was conducting a Part 137 aerial application flight on October 18, 2008, at Silverton, Texas. The commercial pilot, who was the only occupant, was seriously injured in the accident. Physical evidence indicated that the airplane hit an electrical transmission wire. The airplane was equipped with a wire deflector, which was mounted on the cockpit windshield. The wire deflector was bent. In addition, an anti-snag deflector cable, which was supposed to run from the cockpit to the vertical fin, was torn immediately forward of the vertical fin. The spar caps on either side of the vertical spar displayed compression damage, and the spar web had been damaged. The rudder displayed compression wrinkling. The vertical stabilizer had separated from the airplane and wasn't recovered. Investigators determined that aircraft control wouldn't have been possible, and a crash was inevitable.

Investigators reported that the pilot's restraints were faded and appeared worn. The pilot's left lap belt had failed inboard of the adjustment buckle, with the failure area displaying signs of wear and stretching. The cable securing the shoulder harness to the inertial reel had failed just below the connection to the shoulder harness. No identification tags were found on the belt showing the date of manufacture. The airframe logbook showed that all of the restraint cables were replaced in 1997, and the center shoulder harness cable was replaced in 2000. There was no entry found for the replacement of the restraint webbing material.

In the Safety Alert dealing with "Proper Use of Fiber or Nylon Self-Locking Nuts," the Safety Board said that some pilots and mechanics aren't adequately inspecting the nuts they're installing to be sure their fiber or nylon inserts are in good condition and won't allow the nuts to loosen under in-flight vibration. The Safety Board notes that the ability of a self-locking nut to really lock degrades with each use. The Safety Board points to the 2011 crash of a North American P-51D into the crowd at the National Championship Air Races in Reno, Nev., as a worst-case example. The pilot and 10 people on the ground sustained fatal injuries, and at least 64 people on the ground were injured. As we previously reported in this column, the Safety Board found that reduced stiffness of the elevator trim tab system allowed aerodynamic flutter to occur at racing speeds. The reduced stiffness was a result of deteriorated locknut inserts that allowed the trim tab attachment screws to become loose and to initiate fatigue cracking in one screw sometime before the accident flight. Aerodynamic flutter of the trim tabs resulted in a failure of the left trim tab link assembly, elevator movement, high flight loads and a loss of control. Contributing to the accident were undocumented and untested major modifications to the airplane and the pilot's operation of the airplane in the unique air racing environment without adequate flight testing.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.


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