AAIB Bulletin: 1/2007 G-MOLY EW/G2006/07/24

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77 © Crown copyrght 2007 AAIB Bulletin: 1/2007 G-MOLY EW/G2006/07/24 ACCIDENT Aircraft Type and Registration: Pper PA-23-60 Apache, G-MOLY No & type of Engines: 2 Lycomng O-320-B3B pston engnes Year of Manufacture: 959 Date & Time (UTC): 7 July 2006 at 645 hrs Location: Lttle Shelford, Cambrdge Type of Flight: Prvate Persons on Board: Crew -  Passengers - None Injuries: Crew - None Passengers - N/A Nature of Damage: Damage to left wing tip, pitot mounting, left flap and left landng gear drag lnk Commander’s Licence: Prvate Plot’s Lcence Commander’s Age: 54 years Commander’s Flying Experience: 2,242 hours (of whch 34 were on type) Last 90 days - 29 hours Last 28 days - 5 hours Information Source: Arcraft Accdent Report Form submtted by the plot and arcraft examnaton by the repar agency Synopsis Whle on the ground, the plot nadvertently operated the landng gear retracton lever resultng n the collapse of the left gear and causng damage to the arcraft. The arcraft ant-retracton system was found to have been n the ‘ FLIGHT ’ poston, thus allowng the gear to retract whle on the ground. History of the flight The aircraft had completed an uneventful flight from Whte Waltham to Lttle Shelford n Cambrdgeshre. Havng landed on the easterly runway, the arcraft was taxed off the runway and, whle statonary, the plot nadvertently operated the landng gear retracton lever. Both left and rght landng gear ‘UNLOCKED ’ lghts llumnated. Realsng hs mstake, the plot stopped both engnes n order to lmt the damage and attempted to manually pump the landng gear nto the down poston. The rght landng gear ‘DOWN AND LOCKED ’ ndcaton dd llumnate, however the left landng gear collapsed causing damage to the left wing tip, left flap and ts operatng mechansm. The sngle occupant exted the aircraft without difficulty. The arcraft was jacked, the left landng gear lowered and all three landng gear ‘ DOWN AND LOCKED ’ ndcatons then llumnated. 78 © Crown copyrght 2007 AAIB Bulletin: 1/2007 G-MOLY EW/G2006/07/24 System description The arcraft has a hydraulcally actuated retractable trcycle landng gear system; each landng gear leg s ndvdually actuated by a hydraulc actuator. When the landng gear s selected DOWN, hydraulc pressure causes each actuator to extend a drag lnk on the respectve gear leg untl the lnk reaches an over-centre position. The final movement of the actuator causes a mechancal lock to lock the drag lnk n the over-centre poston. Once the landng gear has locked down, mcroswtches for each gear leg trgger ther respectve green lghts n the cockpt and the gear selector returns to the neutral poston. When the gear s selected UP, the actuators retract causng the downlocks to unlock and the drag lnks to collapse. Once the gear s locked up, mcroswtches cause an amber lght n the cockpt to llumnate and the gear selector returns to the neutral poston. When no lghts are llumnated the landng gear s n an ntermedate poston. If the engne-drven hydraulc pump fals, an emergency hand pump can be used n ts place. In the event of a hydraulc system falure caused by a lne rupturng, an emergency CO 2 bottle can be actvated to blow the landng gear down. The aircraft is fitted with an anti-retraction system to prevent the landng gear from retractng when the arcraft s on the ground. A landng gear ant-retracton valve s located on the left man gear strut housng. Ths restrcts hydraulic fluid pressure from building up in the retraction system untl the landng gear strut s fully extended, e the arcraft weght s no longer on the wheels. Aircraft examination Fgures  and 2 respectvely show the ant-retracton valve in the closed position, ie aircraft in flight, and the open poston, e arcraft on the ground. The actuatng rod s attached to the left man landng gear; when the oleo s n the compressed poston, the rod s pushed Anti- retraction valve Actuating rod Operating arm Figure 1 Ant-retracton valve n closed poston - aircraft in flight Figure 2 Ant-retracton valve n open poston - arcraft on ground 79 © Crown copyrght 2007 AAIB Bulletin: 1/2007 G-MOLY EW/G2006/07/24 up whch n turn pushes the valve operatng arm up. Examnaton of the ant-retracton valve showed that the operatng arm had been stuck n the closed poston. Debrs and corroson n ths area had bult up causng the operatng arm to become stuck. In the opnon of the repar agency t had been n ths condton for some tme and thus represented a dormant falure. Wth the ant-retracton valve n the ‘ FLIGHT ’ poston t was possble for the landng gear to retract when the arcraft was on the ground. The operatng arm was manually freed, the sprng pulled the operatng arm nto the ground poston, and the valve then operated correctly. The Pper Apache servce manual requres a check of the ant-retracton system at every 50 hour nspecton. The last check on G-MOLY was an annual nspecton carred out on the 7 February 2006.