Plane & Pilot
Saturday, May 1, 2004

Known And Unknown Deficiencies

It’s both the pilot’s and mechanic’s responsibility to find faulty equipment

While the FAA makes the pilot responsible for determining whether or not an aircraft that he or she is about to fly is airworthy, the pilot must rely to a great extent on what others have determined about the airplane. It’s relatively easy for a pilot to check paperwork to determine whether or not an aircraft has undergone required inspections, to check that compliance with airworthiness directives is current and to ensure that required documents are on board. What’s not so easy is to explore the dark recesses of an airframe or engine compartment in order to check every bit of maintenance, which has been signed off as being complete. However, a pilot needs to be knowledgeable enough to recognize when an in-flight problem may be related to a mechanical or system deficiency. The pilot also needs to know possible ways to work around the unknown deficiency. Sometimes, this involves “undoing” whatever you did just before the problem appeared.

Occasionally, NTSB accident investigators find that a pilot wasn’t terribly smart when taking off, knowing that there was something wrong with the aircraft. The Safety Board often describes this in Probable Cause statements by saying that the pilot “attempted flight with known deficiencies in equipment.” Unfortunately, whether the deficiency was known or unknown, the outcome can be the same.

Piper PA-28RT-201
On July 2, 2002, at 3 p.m., a Piper PA-28RT-201 operated by a flight school struck the ground during initial climb after takeoff from Lebanon Municipal Airport in Lebanon, Tenn. The Part-91 instructional flight was being operated VFR and the aircraft had been flown to Lebanon from Nashville, Tenn. The flight instructor and the private pilot who was receiving instruction sustained fatal injuries, and the commercial-rated passenger who was sitting in the back received minor injuries.

During the engine run-up, the passenger noticed that the checklist was not used. However, a magneto check was performed. It indicated that the left magneto operated normally, but when the right magneto was selected, the engine lost power. The pilot and the CFI made the decision to continue the flight on one magneto, since it had been done successfully in the same plane during the previous week.

The flight took off from runway 19. When the airplane was passing over trees, the passenger heard the CFI tell the private pilot to “watch the airspeed, and keep it straight.” The passenger looked out of the window and noticed that the airplane was slightly nose-up and felt the “airplane sinking.” The CFI took over the flight controls and banked the airplane to the right. The passenger remembers seeing a barn from the air and the airplane hitting a power line.


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