AAIB Bulletin: 8/2008

Full document text

96 © Crown copyrght 2008 AAIB Bulletin: 8/2008 G-CYLS EW/C2007/12/11 ACCIDENT Aircraft Type and Registration: Cessna T303 Crusader, G‑CYLS No & Type of Engines: 2 Contnental Motors Corp. TSIO-520-AE pston engnes Year of Manufacture: 982 Date & Time (UTC): 3 December 2007 at 06 hrs Location: Guernsey Arport, Channel Islands Type of Flight: Prvate Persons on Board: Crew -  Passengers - None Injuries: Crew - None Passengers - N/A Nature of Damage: Damage to arcraft nose and propellers Commander’s Licence: Arlne Transport Plot’s Lcence Commander’s Age: 39 years Commander’s Flying Experience: 5,400 hours (of whch 6 were on type) Last 90 days - 52 hours Last 28 days - 2 hours Information Source: Arcraft Accdent Report Form submtted by the plot Synopsis Shortly after touchng down after a normal approach, the nose landng gear collapsed, causng substantal damage to the arcraft. It was establshed that the nose gear actuator lockng lugs had faled, allowng the nose gear to unlock and collapse forward on touchdown. Evdence was found of pre-exstng cracks n the lockng lugs; however, t was not determned by what mechansm the cracks had propagated. History of the flight The plot approached Guernsey from the north and was gven clearance for a rght-hand base leg jon for Runway 27. On base leg, he selected the first stage of flap and lowered the landing gear and recalled hearing the usual noses and observng the normal trm changes. He confirmed three green ‘down and locked’ indications were showng and that the gear was actually down by looking in the landing gear viewing mirror. On final approach, he selected landing flap and received the clearance to land. The approach was reportedly stable, wth no crosswnd and the arcraft touched down on the runway just beyond the numbers. On lowerng the nose, t contnued to drop and t quckly became apparent from the nose-down atttude and the damage to the now statonary propellers, that the nose gear had collapsed. The arcraft travelled n a straght lne wth ts nose scrapng on the runway surface, comng to rest about 300 m along the runway. The plot was unnjured and exted normally va the rear door. 97 © Crown copyrght 2008 AAIB Bulletin: 8/2008 G-CYLS EW/C2007/12/11 Aircraft information Background information The Cessna T303 Crusader s an all-metal, low-wng, sx-seat, twn-engned arcraft wth a trcycle landng gear. A total of 315 were manufactured. G‑CYLS was seral number T303-00005 and was bult n 982. It held a current EASA Certificate of Airworthiness, valid until 8 May 2008. Aircraft damage The arcraft sustaned structural damage to ts nose, whch had buckled. It was also heavly abraded on ts undersde from sldng along the runway surface, Fgure . The propellers were also badly damaged from strkng the runway. Closer examnaton revealed that the lockng lugs of the nose gear actuator had fractured, causng the gear to unlock and collapse forward as weght was appled to t on landng. Nose landing gear description The nose gear, whch retracts forwards, conssts of a shock strut mounted n a trunnon assembly, a nosewheel, shmmy damper and a double-actng hydraulc actuator for extenson and retracton. The upper end of the actuator is fixed to the aircraft structure and the end of the actuator ram s attached to the rear of the nose gear. Durng gear extenson, hydraulc pressure s ported to retract the actuator ram, causng the nose gear to extend rearward. When fully down, sprng-loaded lockng hooks on the end of the ram engage onto downlock pns on the body of the actuator. The gear s thus mechancally locked n the down poston by the body of the actuator, whch acts as a rgd drag strut. The downlock pns are located n lockng lugs on the actuator body and are retaned by roll-pns. Nose gear actuator information The actuator fitted to G‑CYLS was manufactured in 1981 and was identified with part number 1280514‑11 and seral number 33. Enqures of the arcraft manufacturer revealed that there are no overhaul or specal nspecton requrements for the nose gear actuator. It s therefore possble that the faled actuator had been on the arcraft snce arcraft buld. Nose gear actuator examination The faled actuator was subjected to detaled metallurgcal examnaton. Both lockng lugs had fractured, lberatng a segment of each lug and ts downlock pn, Fgure 2. However, the roll-pns had remaned n the lugs. Of the two fractures on each lug, one was solely the result of ductle overload and thus secondary to the ntal falure; the other exhbted much less deformaton. One of the two ‘prmary’ fractures was very flat in appearance with no obvous sgns of ductle overload and was also Figure 1 Photograph of G‑CYLS showing damage to nose of aircraft 98 © Crown copyrght 2008 AAIB Bulletin: 8/2008 G-CYLS EW/C2007/12/11 consderably more dscoloured by corroson products than the other, Fgure 3. The other prmary fracture dffered n havng a lesser degree of dscoloraton and a clearly vsble regon of ductle overload. Detaled fractographc examnaton, usng optcal and scannng electron mcroscopy, showed the prmary fractures to be generally ntergranular n nature, wth no evdence of fatgue propagaton. It was not possble to state wth any certanty what mechansm had caused the prmary fractures. Metallographc examnaton of the lugs revealed an unfavourable gran orentaton around the ends of the lugs, such that the appled loads were actng along the gran boundares; ths was evdenced by the drectons of the prmary fractures beng parallel to the gran boundares. Discussion The dscoloraton of the prmary fractures of the actuator lockng lugs s ndcatve that these had been present for some tme, n contrast to the fresh appearance of the final ductile overload failures that resulted in the nose