Lessons Learned

Technical Related Lessons

The flight crew should check and validate primary flight and engine instruments during the low speed (below 80 knots) portion of each takeoff. If any display appears to be unusual or inoperative, the takeoff should be rejected. (Threat Categories: Incorrect Piloting Technique, Flight Deck Layout/Avionics Confusion)

  • During the takeoff roll, per procedure, the captain should have aborted the takeoff immediately upon discovery that his airspeed indicator was not operating properly. Instead he relied on the first officer's airspeed calls and continued the takeoff.
  • Once airborne, knowing he had an unreliable airspeed indicator the captain did not look between his 3 sources and fly using the one he deemed correct.
  • When he got the stick shaker (impending stall indication) the pilot did not apply standard stall recovery procedures. He was confused with conflicting high and low speed warnings and did not appear to understand that the stick shaker is not commanded from the airspeed, but from the angle-of-attack sensor.

While in flight, a suspected malfunctioning airspeed display should be cross checked with other cockpit displays, including standby displays, in order to determine the appropriate display to use for maintaining safe airspeed. (Threat Category: Incorrect Piloting Technique, Crew Resource Management)

  • The flight crew seemed to be aware that airspeed was not being correctly displayed, but were confused as to which display(s) were correct. A cross check, or comparison of the three indicators might have resulted in identification of the incorrect indication, and reversion to use of another indicator, or transfer of control between the pilots.  
  • Human factors studies have shown that when complex, time-critical safety decisions must be made, humans will channel their attention, and situational awareness will degrade, leading to an increase in errors. For this reason, having multiple crewmembers complementing each other is a widely accepted safety aid. In this accident, the investigators cited the lack of crew resource management as a factor in the progression of the accident sequence.

Common Theme Related Lessons

If an aircraft is expected to be out of service for an extended period of time, or will be susceptible to pitot system blockage due to severe weather, dust, debris, or insects, pitot covers should be installed to mitigate the possibility of those blockages occurring. (Common Theme: Organizational Lapse)

  • The investigation could not positively establish that pitot probe covers were installed for the entire maintenance period. Uncovered pitots allowed the local mud dauber wasp to build a nest in, and clog the captain's pitot probe, resulting in an incorrect airspeed indication during takeoff and climb.
  • The prescribed air data system checks were not performed after a prolonged maintenance period. Investigators believed that if the prescribed checks had been performed, the plugged pitot would most probably have been discovered.

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