Spiral During Flight Training

On April 6, 1999, an instructor and student departed in a Cessna 152 on a one-hour training flight to practise climbing, descending, and turning exercises. Near the end of the flight, a witness to the accident heard an aircraft flying overhead, then the engine noise stopped. This caused the witness to look in the direction of the aircraft; it was in a nose-down attitude, and it rotated twice to the right before disappearing behind a treeline located within 1000 ft of the witness. The aircraft struck trees at high speed and crashed in a swamp. The witness estimated that the aircraft was well below 2000 ft above ground level (AGL) when first observed. The instructor and student received serious injuries and succumbed later to their injuries. This synopsis is based on the Transportation Safety Board of Canada (TSB) Final Report A99O0079.

Visual meteorological conditions prevailed at the time of the occurrence. The aircraft was certified, equipped, and maintained in accordance with the existing regulations. The engine was disassembled and no discrepancies were noted that would have precluded normal engine operation prior to the accident. The wreckage was first examined at the crash site, then removed to a salvage facility and re-examined. None of the damage was identified as pre-impact. Examination revealed that the aircraft's rate of descent was shallow and that the wings were level at impact. The flaps were in the up position. There was no indication of pre-impact structural failure and, because of the severe impact damage and fragmentation of the airframe, it could not be determined if a flight control malfunction had occurred. The airspeed indicator (ASI) was forwarded to the TSB Engineering Branch for examination. Examination of the ASI did not provide any information with respect to airspeed indication at the time of impact. There was no pre- or post-crash fire.

The instructor pilot was certified and qualified in accordance with existing regulations to conduct the training flight. The student pilot had had a familiarization flight in May 1998 and had accumulated less than ten hours by the end of the year. The accident flight was the student's first flight in 1999. As of the accident date, the student had not obtained a pilot medical; therefore, there was no pilot file for review at Transport Canada.

The flight training curriculum requires that, during the turning exercise, the instructor demonstrate a steep turn (45º of bank or greater) and the student practise these turns. It is important to effectively monitor the aircraft attitude during a steep turn to avoid inadvertent entry into a spiral manoeuvre. Should a spiral manoeuvre be recognized, the correct recovery procedure is to close the throttle, level the wings using co-ordinated control inputs, and ease out of the dive. Radar data was retrieved in an attempt to identify the aircraft's movements; however, the TSB determined that the aircraft's altitude at the time of the spiral manoeuvre was below radar coverage and, therefore, not indicated.

Analysis — The weather was not a factor in the accident. Flight instructors are aware of the dangers of allowing a spiral to develop at low altitude and, especially, continue below 2000 ft AGL. The TSB could not determine why a spiral was continued to an altitude from which a safe recovery could not be performed. The wing impact damage indicated that the aircraft was probably entering a recovery attitude prior to striking the trees. The sudden absence of engine noise that captured the witness's attention likely resulted from the pilot initiating the spiral recovery procedure. It was evident that the engine was capable of producing power. The TSB could not determine why the aircraft entered a spiral manoeuvre.