page_title: USAir Flight 5050
section_title: Rudder trim issue
hierarchical_section_title: USAir Flight 5050 / Accident analysis / Rudder trim issue
caption_attribution_description: English: Rudder Trim Control (red highlight-added) and rudder position indicator (yellow highlight-added),
context_page_description: USAir Flight 5050 was a passenger flight that crashed on takeoff from LaGuardia Airport in Queens, New York. As the plane took off from LaGuardia's runway 31, the plane drifted to the left. After hearing a loud bang, the pilots attempted to abort the takeoff, but were unable to stop the plane short of the end of the runway. The plane continued past the end of the runway and plunged into Bowery Bay. Two passengers were killed.
context_section_description: Analysis of the digital flight data recorder revealed that the rudder trim had moved to the far left limit, while the plane was parked at the gate.  Since power to the DFDR was off, while parked at the gate, the NTSB could not determine what caused the rudder trim to move to that extreme limit.  It was speculated that someone was sitting in the jumpseat (which is located directly behind the control pedestal) had rested their feet on it and inadvertently toggled the trim knob. This knob used to have a raised flat and straight portion protruding from it.  Subsequent to this event, all 737s were retrofitted with a rounded rudder trim knob – and a higher ridge around the aft section of the pedestal in an effort to prevent a similar occurrence. That mistrim of the rudder should have been discovered when the Before Takeoff checklist was read, but the pilots failed to ensure the rudder was in the zero trim (neutral) position at that time.  The captain also failed to detect that the rudder pedals were unequally displaced by 4.25 inches (108 mm) and the nosewheel steering was turned to 4 degrees left, during the taxi out from the gate to the takeoff position on the runway.
  When the rudder trim is centered to zero degrees, as required for takeoff, the rudder pedals would be matched so that the captain's legs would be extended the same amount, for each pedal, and the plane's nosewheel steering would not keep trying to turn the plane to the left, during taxi operations (See graphic).
  The NTSB could not understand why the captain failed to detect the mistrimmed rudder (as evidenced by the abnormal displacement of the rudder pedals and the tendency for the plane to keep trying to turn left), during the time that the plane was taxied to the takeoff position.
  The safety issues discussed in the report are the design and location of the rudder trim control on the Boeing 737-400, air crew coordination and communication during takeoffs, crew pairing, and crash survivability. Safety Recommendations addressing these issues were made to the Federal Aviation Administration and the Port Authority of New York and New Jersey.
caption: Rudder trim control (in red) and rudder trim position indicator (in yellow), on the rear of the center console, between the pilot seats of the B737-400. Note that the indicator needle is in the center of the gauge—the required position when pilots finish running the pre-start and pre-takeoff checklists
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