Parts Catalog for Piper PA-34 Seneca II

suggesting that a washer/spacer had been present between the downlock link and the nose landing gear 17 leg at some time. However the only washer/spacer specified to be fitted in this location has an internal diameter of 19 mm, which just fits over the bolt. Anil Examination of the area of the bolt hole at the top of the nose landing gear leg, where the downlock link was attached, showed deformation of the steel and ovality of the hole (photograph No. 6) which had occurred over a period of time prior to the bolt failing. There was, however, no marking on the adjacent surface that could be associated with a washer or with contact with the protruding bush. Examination of the aircraft's maintenance records showed that work had been carried out on the nose landing gear of the aircraft on a number of occasions since its importation into the UK from the USA. In February 1990, a new bush had been fitted to this bore of the downlock link. Subsequently there had been three occasions, March and April 1990 and January 1991, when the downlock link/nose landing gear leg bolt would have been removed to enable maintenance work to be carried out. Another Piper PA 34 200T aircraft which had been maintained by the same maintenance organisation was examined and the downlock link/nose landing gear leg bolt removed. It was found to be correctly assembled except that there was no washer fitted under the head of the bolt. The bolt had been replaced by that maintenance organisation in October 1990. The Maintenance Manual and the Illustrated Parts Catalogue for this model, the Piper PA 34 200T, were found to give no specific instructions or guidance regarding the location of washers/spacers when assembling this bolt. However it was found that guidance was given, in pictorial form, on the assembly of this bolt in the Illustrated Parts Catalogue for the Piper PA 34 200.bnog so The reason for the displacement of the bush was unclear. The appearance of the damage to the protruding end, ie cracking, local deformation and marks on the outer surface, was consistent with difficulties having been experienced during the fitting operation of the bush or by the bush working its way out of the downlock link during service. The faint annular marking on the inner face of the downlock link suggested that a washer may have been present at some time, although the size of the mark was not consistent with that of the washer that should have been used in this assembly, and there was no similar evidence on the adjacent face of the nose landing gear leg. The manner in which the bolt head had pulled into the bore of the downlock link, as a consequence of the absence of a washer in that position, appeared to confirm that the bush had been protruding at the time of the last assembly. The only other conceivable possibility was that one or two washers had been fitted at some time between the downlock link and the nose landing gear leg and that their internal diameter was large enough to allow them to fit over the bush, such that the bush could then be drawn through during tightening of the nut. However, in order for this to have occurred the bush and the washers would have had to be accurately aligned when assembled in the horizontal position and this would have been extremely difficult. The evidence of the build-up of a grease-like deposit on the protruding surface indicated that these washers had not been fitted during the last occasion upon which the bolt had been fitted. 18 With regard to the fracture of the bolt, which had occurred close to the interface between the downlock link and the nose landing gear leg, it is possible that although the bolt was clearly defective and therefore susceptible to fatigue damage, its failure could have been assisted by the increased bending loads which would have been introduced by the offset between the downlock link and the nose landing gear leg resultant from the displacement of the bush. The ovality and deformation evident at the downlock link end of the bolt hole in the nose landing gear leg certainly suggested that incorrect loading of the bolt had occurred. During the course of this investigation the manufacturer's agency company within the UK was consulted with regard to any known problems with the nose landing gear of this aircraft type. They reported that they had experienced a similar problem with a downlock link/nose landing gear leg bolt failing approximately two years previously, but that the failure had not resulted in an accident. As a result, this company had instigated a 2000 hour scrap life on the bolts fitted to their own fleet of Piper PA 34 aircraft. No Mandatory Occurrence Report (MOR) was raised because such reporting is not mandatory for aircraft below 2,300 kg. As a result of the above findings, the following recommendations have been made to the CAA for them to address internationally through consultations with the Federal Aviation Administration (FAA): od bus 92-10.0 alod The CAA introduce a 'one-time' inspection be carried out on all Piper PA 34 aircraft to ensure that the specified washer is fitted to the downlock link/nose landing gear bolt; that such bolts have the correct head markings and the surface condition of their shanks is satisfactory. 92-11. The CAA ensure that adequate instructions and guidance are given in the Piper PA34 200T Maintenance Manual and Illustrated Parts Catalogue to enable correct assembly of the downlock link/ nose landing gear bolt. 92-12. The CAA require that a suitable life be determined for downlock link/nose landing gear bolts on Piper aircraft.donam d 92-13. to si gribitory wood bed bra The CAA consider extension of the Mandatory Occurrence Reporting system to include aircraft under 2,300 kg maximum gross weight in the Public Transport and Aerial Work categories, and take measures aimed at ensuring that the service experience of operators and maintainers is fed back to the manufacturer and expeditiously shared with other relevant UK operators and maintainers. (This recommendation was also previously made following the investigation into Aerospatiale Twin Squirrel, G-WMPA, on 30 December 1990, AAIB Bulletin 12/91.) 19 Photograph No. 1. Double fatigue failure of the bolt. Photograph No. 2. Head of failed bolt (left) & "good" bolt (right). 20 20 Photograph No. 3. Protruding bush in the downlock link. Photograph No. 4. Side view of the bush showing the crack and deformation lip. 21 Photograph No. 5. Bolt head markings in the downlock link and bush. Photograph No. 6. Ovality of the bolt hole in the top of the nose landing gear leg. 22