Cessna 172F, VH-ECT

The pilot of a Cessna 172 was conducting a solo navigation flight from Essendon with planned landings at Latrobe Valley and Leongatha. At approximately 1030 EST the pilot broadcast on the Latrobe Valley common traffic advisory frequency (CTAF) of 126.0 MHz his intention to make a full stop landing on runway 03. Witnesses at the airfield heard the sound of engine power increasing and saw the aircraft commence what appeared to be a missed approach from about 100 ft on short final. They reported that the aircraft entered a steep left climbing turn onto a reciprocal heading with flaps fully extended. At an estimated height of about 300 ft the wings were seen to roll level and the aircraft, with a nose high attitude, "fishtailed". Then with the engine noise unchanged, the aircraft pitched nose down and impacted the ground adjacent to the runway. The pilot was fatally injured, and the aircraft was destroyed by impact forces. The reason for the go-around was not determined.

Weather at the time of the accident was clear sky and unlimited visibility with a light north easterly breeze. There was no other aerodrome traffic.

Examination of the wreckage found no evidence to suggest that the aircraft was not capable of normal operation. The ancillary controls were configured for the approach; that is, flaps set to approximately 40 degrees, elevator trim at a position corresponding to the position for that flap setting, approach speed and power, and carburettor heat ON.

Although there was wear to the rollers, seat rails and the locating holes, the pilot seat locking mechanism was capable of normal operation. The pilot seat stops were fitted to the inboard rail and were of inverted "U"-shaped metal design. They were placed over the rail and secured by a split pin that passed through a slot in the rail. They were similar to seat stops used in many Cessna aircraft.

An inspection of the Cessna 172 parts manual revealed that the seat stop locations were specified differently, depending on aircraft serial number. The stops specified in the parts manual consisted of a flat metal section with a threaded hole in the centre that passed through the slot in the seat rail and secured by a screw inserted through the locating hole in the rail, and screwed into the stop. The forward stop was secured through the most forward slot in the rail and, unlike the specified part, was able to lie forward over the front end of the rail. That installation permitted the seat to be adjusted forward beyond the first locating hole. Marks on the left seat rail indicated that the pin of the pilot's seat might have been incorrectly secured forward of the end of the seat rail. There would have been no indication to the occupant of the seat that the locking mechanism had engaged in that manner, or that the seat was not properly locked into position, other than by close visual inspection.

The rear stop of the pilot's seat was located at a point 410 mm forward of the door rear pillar. The seat of a similar aircraft was set to a corresponding position and when seated at that distance from the controls, a pilot of similar stature to the accident pilot, was unable to reach the flap switch, carburettor heat or elevator trim controls. That pilot was unable to apply any significant forward elevator control and only by pulling back on the control wheel was the pilot able to lean forward sufficiently to reach the throttle in the fully open position.

Flight tests were conducted using a similar aircraft. The aircraft was configured for an approach with a flap setting of 40 degrees and the aircraft trimmed to an approach speed of 60 kt. After applying full power and then using limited elevator and full aileron control inputs only, it was possible to fly a manoeuvre similar to that described by witnesses.

The accident pilot held a Student Pilot Licence and was appropriately qualified to undertake the flight. He held a valid Class 2 medical. Instructors who had trained the pilot reported that although his flying did not reflect the level of skill commensurate with his flying experience, he had satisfactorily demonstrated missed approach manoeuvres in the Cessna 172. They reported that he was able to achieve full control input with the seat adjusted well forward despite his short physical stature.

Flight instructors reported that the pilot had demonstrated his ability to satisfactorily perform go-around manoeuvres in this aircraft. Therefore, it was unlikely that the out of trim elevator forces experienced during the full flap go-around were beyond the physical capability of the pilot.

The possibility of an inadequately secured seat sliding back along the seat rails during the go-around was examined. The pin on the unoccupied right front seat was bent, indicating that it was properly engaged into the seat rail locating hole at impact. However, neither the locking pin on the pilot's seat nor any of the seat rail holes exhibited damage consistent with a properly engaged locking pin. The full flap go-around required considerable forward elevator control input by the pilot to counteract out of trim forces. This would have transferred pressure to the seat backrest, lifting the front of the seat and reducing pressure on the front of the worn seat rail and locking pin. Acceleration forces and the aircraft's nose high attitude may have allowed the locking pin to ride up the chamfered front end of the rail, and the unrestrained seat to move rearward to the aft seat stop.

During take-off, as the pilot applied back elevator control input, postural forces on the seat would have held the pin against the end of the rail and secured the seat. This may explain why the seat did not move rearward during take-off.

The possibility of aircraft mishandling during the initial stages of the go-around and the subsequent loss of control at a low height above the ground cannot be discounted. However, the event as described by witnesses, and confirmed by ground and flight tests, was consistent with the pilot seat sliding back and denying the pilot adequate control input to avoid an accident.

As a result of this investigation, the Australian Transport Safety Bureau simultaneously issues the following Safety Advisory Notices:

SAN 200100223

The Civil Aviation Safety Authority note the safety deficiency identified in this report relating to single-engine Cessna aircraft seat stops and, as a matter of some urgency, alert aircraft owners, aircraft maintenance engineers and pilots to the potentially dangerous consequences of using other than the specified seat stops and to the importance of correctly locating those seat stops and ensuring that the seat pin securely engages a locating hole on the rail.

SAN 200100224

The Aircraft Owners and Pilots Association of Australia note the safety deficiency identified in this report relating to single-engine Cessna aircraft seat stops and consider communicating through the association's journal the potentially dangerous consequences described in this occurrence.

SAN200100225

The Australian Licenced Aircraft Engineers Association note the safety deficiency identified in this report relating to single-engine Cessna aircraft seat stops and consider communicating through the association's newsletter the potentially dangerous consequences described in this occurrence.