CT155204 Hawk - Epilogue

Report / October 19, 2009 / Project number: CT155204 - E Category

Location: South of Cold Lake, Alberta
Date: 2009-10-19
Status: Investigation Complete

The incident occurred during a routine Air to Surface Tactics training mission being flown at low altitude within the borders of the Cold Lake low flying area. The aircraft was being flown from the front seat by a student fighter pilot with an experienced instructor occupying the rear seat. During the simulated transmission of a tactical report the aircraft experienced an un-commanded nose-down pitch change. At the time, the aircraft was flying straight and level at 426 knots and 385 feet above ground level. The aircraft quickly nosed over to approximately four degrees nose down attitude with a peak negative “g” of -0.6. The student pilot initially thought that the instructor had made a stick input to indicate to him that he should be flying lower (the instructor did not do this). The instructor initially thought that the student may have become incapacitated and had fallen on the controls. The aircraft lost about 100 feet before both pilots initiated recovery action by pulling back on the stick.

The instructor estimated it required a 40 to 50 lb pull force to raise the nose above the horizon but he reported stick pressure became normal during the final portion of the recovery and, following a controllability check, the aircraft landed uneventfully at Cold Lake.

The investigation determined that the aircraft experienced a tailplane nose-down trim run-away. A thorough technical investigation was unable to find any fault with the trim system and the aircraft ground checked and test flew serviceable. The pilots were confident they had not made an inadvertent trim input.

Based on a simulator trial and, as stated in the Aircraft Operating Instructions, an un-commanded full trim input can be easily countered by the pilots. However, both pilots were startled and neither pilot considered that it could have been a tail plane trim run-away situation. The altitude loss was exacerbated by the student’s delayed response and confusion regarding why the stick was moving forward on its own. Previous exposure / training to a run-away trim emergency in a controlled environment would improve the aircrew’s familiarity with the symptoms and likely result in a quicker response. Additionally, such practice would build pilot confidence in their ability to safely control the aircraft during an extreme out-of-trim condition.

The investigation recommended that prior to participation in a low level training phase pilots complete a full runaway nose-down trim exercise in the simulator. It was also recommended that a “Tail Plane Run-away Trim” procedure be added to the Hawk critical emergency checklist.

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