AAIB Bulletin: 11/2009

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102 © Crown copyright 2009 AAIB Bulletin: 11/2009 G-ATEW EW/G2009/05/31 ACCIDENT Aircraft Type and Registration: Piper PA-30 Twin Comanche, G-ATEW No & Type of Engines: 2 Lycoming IO-320-B1A piston engines Year of Manufacture: 1965 Date & Time (UTC): 30 May 2009 at 1340 hrs Location: Sturgate Airfield, lincolnshire Type of Flight: Private Persons on Board: Crew - 1 Passengers - 1 Injuries: Crew - None Passengers - None Nature of Damage: Damage to both propellers and damage to fuselage and wing underside (beyond economic repair) Commander’s Licence: Private Pilot’s Licence Commander’s Age: 66 years Commander’s Flying Experience: 711 hours (of which 475 were on type) Last 90 days - 0.6 hours Last 28 days - 0 hours Information Source: Aircraft Accident Report Form submitted by the pilot and further enquiries by the AAIB Synopsis During the ground roll following a firm landing, all three landing gear legs retracted. The aircraft slid along the runway on its belly before coming to rest. There was insufficient information available to determine what had caused the gear to retract. History of the flight The aircraft had departed from Newcastle Airport for a flight to Sturgate airfield. The weather at Sturgate was cAVOK with a south-easterly wind of 8 to 10 kt. The pilot manoeuvred the aircraft to join overhead the airfield at 2,000 feet and then descended to join a downwind leg for Runway 09. He decided to carry out a flaps-up approach to the paved runway which had an unlicensed length of 820 metres. During final approach he made a “Finals gear down” radio call and checked that the single green (gear down and locked) light was illuminated. He did not visually check the gear position using the mirror on the left engine cowling. His passenger, who was also a pilot, also noted seeing the green light. The pilot reported that the aircraft arrived over the runway threshold at 100 KIAS and then he reduced the power and flared slightly. He stated that the aircraft made a harder landing than normal but not “over-hard” and then rolled normally along the runway. After a ground roll of about 300 feet the pilot looked 103 © Crown copyright 2009 AAIB Bulletin: 11/2009 G-ATEW EW/G2009/05/31 to his right and then moved his hand to turn off the fuel pumps. At about the same time he became aware of a sinking feeling which continued until the aircraft was sliding along the runway on its belly. When the aircraft came to rest, his passenger opened the main door and exited the aircraft. The pilot turned off the fuel selectors and the electrical switches before exiting as well. Shortly thereafter the airfield’s fire service arrived at the scene but there was no fire. Landing gear system description The landing gear retraction and extension system of the Piper PA-30 consists of an electric motor and transmission assembly, torque tube assembly, push-pull cables to each main gear leg and a push-pull tube to the nose gear leg. Limit switches are installed which shut off the motor when the gear is either fully extended or fully retracted. The limit switches also operate the gear indicator lights in the cabin. The gear is held in the down position by an over-centre geometric locking mechanism. To prevent the gear from being inadvertently retracted on the ground there is an anti-retraction safety switch located on the left main gear leg which will prevent the gear from retracting until sufficient weight is lifted from the gear to enable the strut to extend to within 0.75 inches of full extension. A gear warning horn sounds if the engine manifold pressure is reduced below 10 to 12 inches while the landing gear is not selected down. Examination of the aircraft The aircraft was examined by the chief engineer from the maintenance organisation based at the airfield. When he entered the cabin of the aircraft he found that the gear selector was in the DOWN position and the electrical master switch was off. He reported that after he turned the master switch on he could hear the ‘whirring’ noise of the landing gear electric motor, but with no movement of the gear it was clear to him that the motor’s drive had sheared. The aircraft was raised and supported with the combination of a crane and jacks. When the aircraft was lifted, the nose gear and right main gear dropped down, but the left main gear only came down to a 45° angle. He pulled the nose gear leg forward which appeared to cause the right main gear leg to lock down, but the left main gear leg did not move. When he tried to pull the left main gear leg down he noticed that there was a bend in the push-pull cable. After cutting this cable the left gear dropped down to the extended position. The engineer assessed that there was no internal wing damage which he would have expected to see if the aircraft had suffered a heavy landing. The aircraft was later determined to be beyond economic repair so no further examination of the aircraft was carried out and the anti-retraction safety switch was not checked. The position of the fuel pump switches in relation to the position of the gear switch is shown in Figure 1. Pilot’s assessment of the cause The pilot considered that either the landing gear had collapsed or retracted. He thought that a retraction might have been caused by the landing gear switch not latching down or perhaps his arm catching it when he moved his hand to turn off the fuel pumps. Since it was a flaps-up landing he did not believe he had made the mistake of reaching for the gear lever instead of the flap lever. Analysis According to the pilot the aircraft made a harder than normal landing and then had a ground roll of about 300 feet. If the gear had not been locked down prior to 104 © Crown copyright 2009 AAIB Bulletin: 11/2009 G-ATEW EW/G2009/05/31 landing, the gear would have collapsed at touchdown. The 300-foot ground roll indicates that the gear was down and locked during the initial part of the landing