de Havilland Canada DHC-6-200, VH-JEA

On 21 January 2005 at about 0830 Eastern Daylight-saving Time, a de Havilland Canada DHC6-200 Twin Otter aircraft, registered VH-JEA, was engaged in commercial skydiving operations at Wilton, NSW, with one pilot and 12 parachutists on board.

The pilot reported that while approaching the drop zone at flight level (FL) 140, he heard a loud noise and noticed the nose locker door detach from the front left side of the aircraft. The door passed in front of the right windscreen before contacting the right propeller. Windows on the right side of the aircraft cabin were broken by debris. The parachutists exited the aircraft and the pilot diverted to Bankstown Airport.

Although the engine indications appeared normal, the pilot suspected that the right engine had developed a vibration. He broadcast a PAN¹ and shut down the engine as a precaution. Following the activation of local standby services at Bankstown, a single engine approach and landing was completed. There were no injuries.

An engineering examination found that damage to the aircraft was consistent with the pilots report. One of the two latches from the nose locker door was found inside the cabin. Damage to fibreglass material attached to the latch was consistent with the door having been torn by aerodynamic forces. The remainder of the nose locker door was not recovered. Examination of the latch and fibreglass material found no indication of a pre-existing defect.

On previous occasions the pilot had experienced some difficulty securing the door as it did not sit flush with the fuselage when in the locked position. He stated that because of this, he was careful about checking the aircraft nose locker door and believed, but could not be certain, that he had checked its security immediately prior to the flight.

During the flight, the main cabin door/locker door warning was continuously illuminated on the aircraft caution annunciator panel. The pilot disregarded the warning as it had been illuminated during previous flights when all doors and lockers had been closed and locked.

To facilitate parachute dropping operations, the main cabin door had been modified and replaced with a roller shutter door installation. The installation engineering order had been prepared by an organisation which held a Civil Aviation Safety Authority (CASA) instrument of approval under Civil Aviation Regulations (CAR) 1988 Regulation 35 (2). The instrument enabled the organisation to approve design modifications or repairs. The engineering order stated:

This roller shutter door modification itself does not require a Flight Manual Supplement. There must however be present in the Flight Manual a section or Supplement approving door off/open operations.

The engineering order did not contain detail as to how the door warning system should be modified following the roller door installation. The installation was undertaken in accordance with the engineering order, with the result that the associated cabin door/locker door warning annunciator was continuously illuminated.

The Flight Manual section or supplement PSM 1-62-1A, approving main door open or main door off operations, could not be located.

The aircraft operations in support of skydiving activities, although an essential element of the commercial enterprise, were conducted as private operations. Consequently, the operator was not required to maintain any flight operations or flight standards manuals beyond that provided in the Twin Otter Aircraft Flight Manual. It was required to comply with the procedures and requirements of the Australian Parachute Federation and CASA as specified in a Deed of Agreement between the two organisations.

1 Urgency message follows (international signal)

The pilot had experienced difficulty with securing the locker door on previous occasions as it could not be placed into a position that was flush with the fuselage. This created a potential for air flowing under the nose locker door to open it. Damage to the recovered components was not consistent with failure of the lock mechanism; however, failure of the other lock may not be discounted. Given the difficulty in securing the nose locker door, it is likely that it had not been properly secured prior to the occurrence flight.

The main cabin door/locker door warning annunciator was continuously illuminated and was therefore no longer effective as a warning. Consequently, the operational safety intent of the original door warning system design had been negated by the engineering for the modified door.

As a result of this occurrence, the aircraft operator obtained a revised engineering order specifying that the main cabin door open warning system be deactivated. The modified system now provides the pilot with a warning should the nose locker door not be secured.

The aircraft operator also incorporated the required supplement, approving main door open or main door off operations, into the Aircraft Flight Manual.