AAIB Bulletin: 8/2008 G-BOWO EW/C2007/10/03

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92 © Crown copyrght 2008 AAIB Bulletin: 8/2008 G-BOWO EW/C2007/10/03 ACCIDENT Aircraft Type and Registration: Cessna R82 Skylane RG, G-BOWO No & type of Engines:  Lycomng O-540-J3C5D pston engne Year of Manufacture: 978 Date & Time (UTC): 6 October 2007 at 600 hrs Location: Wolverhampton (Halfpenny Green) Airfield, W Midlands Type of Flight: Prvate Persons on Board: Crew -  Passengers - 2 Injuries: Crew - None Passengers - None Nature of Damage: Damage to left man landng gear and talplane Commander’s Licence: Commercal Plot’s Lcence Commander’s Age: 45 years Commander’s Flying Experience: 2,463 hours (of whch 25 were on type) Last 90 days - 46 hours Last 28 days - 5 hours Information Source: Arcraft Accdent Report Form submtted by the plot and metallurgcal examnaton of components Synopsis The arcraft landed wth the left man landng gear not fully down. Metallurgcal examnaton showed that ths was due to the separaton of the landng gear pvot assembly whch had resulted from a cyclc fatgue mechansm. There s a hstory of smlar falures on the R82 and the 72RG whch share a smlar, but not dentcal, desgn of the pvot assembly to that on G-BOWO. History of the flight The arcraft was approachng Wolverhampton followng an uneventful flight when the pilot selected the landing gear down. However, he dd not receve a green ‘down and locked’ ndcaton. He re-cycled the landng gear several tmes, but to no aval. He then performed a low fly‑past of the ATC tower and was informed that the left man landng gear was not fully down. He attempted to lower the landng gear usng the manual hydraulc pump and attempted ‘energetc’ manoeuvres n roll and ptch n an attempt to dslodge the gear, all wthout success. Havng brefed the passengers, the plot carred out a landng on the grass Runway 0; the arcraft contnued n a straght lne untl the left wng began to drop and the arcraft then departed to the left, comng to rest on the sde of the adjacent tarmac Runway 0. 93 © Crown copyrght 2008 AAIB Bulletin: 8/2008 G-BOWO EW/C2007/10/03 System description The arcraft has a hydraulcally actuated, retractable, trcycle landng gear system; each landng gear leg s ndvdually actuated by a hydraulc actuator suppled by an electrcally operated hydraulc power pack. When the landng gear s selected DOWN, hydraulc pressure causes a rotary actuator to operate a pvot assembly va a splned shaft, and each man landng gear strut rotates forward and outboard (see Fgure ). Once the landng gear has locked down, mcroswtches for each gear leg trgger a respectve green lght n the cockpt, and the gear selector returns to the neutral poston. An emergency hand pump s avalable for emergency extenson of the gear. A nose landng gear squat swtch prevents nadvertent retracton whenever the nose gear strut s compressed. Recent maintenance history of the aircraft There had been a reported loss of hydraulic fluid from the rght brake for some weeks pror to the accdent, but no cause had been identified. Following recovery of the arcraft after the accdent, the actuator assembly was removed, whch revealed the surroundng area to be awash with brake fluid. There was no hydraulic leak from the landng gear actuators. In September 2006 G-BOWO experenced a hard landng on the nose landng gear n gusty wnd condtons, whch was reported nAAIB Bulletn 2/2006, file ref EW/G2006/09/02. Damage was reported to be lmted to the collapse of nose landng gear and damage to the propeller. No nspecton was carred out on the man landng gear pvot assembly. Actuator Sector gear Splined shaft - location of fracture Pivot assembly Figure 1 R82 Man landng gear pvot assembly 94 © Crown copyrght 2008 AAIB Bulletin: 8/2008 G-BOWO EW/C2007/10/03 Metallurgical examination The detached pvot assembly was returned to AAIB for metallurgcal examnaton. The pvot assembly had separated n the area of the splned shaft. The fracture surface had been partally damaged by smearng durng rotatonal movement, most lkely caused durng the repeated attempts to operate the gear pror to the landng. A number of fatgue fracture ntaton stes were found at the edge of the fracture face, adjacent to a lubrcatng hole (see Fgure 2). The examnaton concluded that the separaton of the pvot assembly had resulted from a cyclc fatgue mechansm durng normal functonng of the landng gear n servce. Previous safety action A Servce Bulletn (SB), reference SEB90- and enttled ‘Main Landing Gear Pivot Inspection’, was publshed n 990. It s applcable to the Cessna 72 and 82 models wth retractable landng gear, for whch the pvot assembly desgn s smlar, however G-BOWO, Seral Number R820046, was amongst a number of R82 arcraft not affected by the SB. The SB requred nspecton of the man landng gear pvot for cracks n the splne area; replacement pvots were avalable whch were desgned wth an mproved fatgue lfe. The SB also states that: ‘this inspection must be repeated any time an airplane has experienced a landing gear overload condition or if the brakes have a “spongy” operation that cannot be attributed to brake component wear or improper servicing.’ An accdent occurred n 99 to a Cessna Model 72RG, N9592B whch made an ntentonal wheels-up landng at DuPage Arport, West Chcago, Illnos followng repeated unsuccessful attempts to lower the landng gear. Metallurgcal examnaton by the Natonal Transportaton Safety Board (NTSB) showed that: ‘the splined aluminium shaft on the right main landing gear pivot assembly had failed in torsional overload. Cracks were observed at the roots of many of the spline teeth and were observed to have propagated a significant distance into the shaft.’ The NTSB found that there have been a significant