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During the landing as the main wheels touched down, the aircraft began to shudder severely and pulled to the right. All attempts by the pilot to regain directional control were unsuccessful and the aircraft ran off the side of the runway. After entering the lightly grassed flight strip, the turning effect increased and the aircraft began to slide sideways. The abnormal side loadings imposed during the slide caused the left main landing gear to collapse. The investigation found that a substantial amount of the threaded section of the nut which secures the right main landing gear torque link tie bolt had stripped allowing the two halves of the torque link to separate. The right main wheel assembly was then free to oscillate up to ninety degrees to the direction of travel as the landing loads were applied. The pilot was not able to apply enough steering control to overcome the effects of the oscillations. The investigation also found that the left and right main landing gear torque links were installed incorrectly. The left set was fitted to the right landing gear and vice versa. This incorrect fitment had the effect of placing excessive tension loads on the link shear nut assembly causing it to fail by stripping the nut threads. Furthermore, neither of the torque link tie bolt assemblies were of the type specified by the manufacturer for this torque link installation. The bolts and shear castellated nuts were of the type used with the original torque links fitted to this aircraft model. The design of the original torque links was significantly different to the modified type fitted to the accident aircraft. With the original links, all torque stresses were borne against the mating surfaces of the link halves and the tie bolt assembly carried only shear loads. The later modified links require the tie bolt to carry some of the torque loads in tension. The incorrect fitment of the failed torque links caused a substantial increase in the normal tension loads on the tie bolt assembly. The shear nut and link bolt assembly was not able to withstand these additional tension loads. In July 1986 the Australian Department of Aviation issued an Airworthiness Directive (AD) based on information contained in the manufacturers Service Bulletin (SB) 746A. The AD required operators to inspect all aircraft models which were not fitted with the torque link replacement kit called for in SB 746A. This AD also recommended that the replacement kit be fitted at the earliest opportunity. Subsequent to the issue of the Australian AD the manufacturer issued two updates to the SB 746A as SB 746B dated 11 June 1991 and SB 746C dated 15 September 1992. SB 746B required the replacement of the torque link connecting nut and bolt to prevent the original shear nut from stripping. The Australian AD had not been revised to reflect the later information contained in SB 746B and SB 746C. SB 746C required the inspection of the torque links for cracks within ten hours. If any cracks were found the torque links were to be replaced with torque link kit 765-155 revision G before further flight. If no cracking was detected the links were to be replaced within the next 100 hours of operation. Both SB 746B and SB 746C stated that "compliance is critical". The accident aircraft met compliance with the Australian AD but not with the SB 746 parts B or C. The aircraft log books indicated that the modified torque links were probably fitted to the aircraft prior to July 1990 when it was imported into Australia. Three other aircraft of the same type were inspected during the initial stages of the investigation and it was found that they met compliance with the manufacturers original SB 746A as required in the Australian AD but not SB 746 parts B or C. The investigation was unable to obtain a current, appropriately amended manufacturer's Maintenance Manual or Illustrated Parts Catalogue for this aircraft type that would show the correct method of fitment for the modified torque links. The manufacturer's Australian distributor indicated that the only way such instructions and illustrations could be obtained was for the operators to purchase a total kit number 765-155 revision G which included fitment details. Several local maintenance organisations and operators stated that they had been unable to procure appropriate updated amendments for their Maintenance Manuals or Illustrated Parts Catalogues for several years. The same situation was said to apply to the amendment service for Service Bulletins and Service Instructions. In each case where the torque links were fitted incorrectly or where the shear nut assembly was still in service the operator or maintenance organisation was not in receipt of either SB 746B or SB 746C. SAFETY ACTION As a result of the investigation the Bureau made the following interim recommendation IR930188 to the Civil Aviation Authority on 24 August 1993. It stated: The Bureau recommends that the Civil Aviation Authority: 1. initiate inspections of all aircraft to ensure compliance with Aerostar Service Bulletin 746C; 2. amend AD/TSA-600/33 Amendment 4 to reflect the latest issue of Aerostar Service Bulletin 746C; and 3. assess revisions to manufacturers data which are quoted in Australian Airworthiness Directives and determine the requirements for subsequent amendment to the relevant Airworthiness Directive. [The Bureau had previously recommended similar action. BASI Report B/913/1009, VH-TPM, Recommendation 1 refers]. In response to this recommendation, the Civil Aviation Authority published Airworthiness Directive AD/TSA-600/33 Amendment 5 effective 15 September 1994. However, this Airworthiness Directive amendment did not require compliance with Aerostar Service Bulletin SB 746C which the aircraft manufacturer classifies as "compliance critical" and that SB 746C "supercedes and voids SB 746, SB 746A and SB 746B". In further correspondence with the Civil Aviation Authority the Bureau requested a further review of the Airworthiness Directive to ensure that it accurately reflects the aircraft manufacturers compliance requirements. The Civil Aviation Authority's response to this correspondence stated in part: "This Authority does not agree with your assessment of amendment 5 to AD TSA-600-33". The Bureau has classified this response as CLOSED/NOT ACCEPTED.
General details
Date: 12 August 1993 Investigation status: Completed 
Time: 6:28 UTC  
 Investigation type: Occurrence Investigation 
 Occurrence type: Control - Other 
Release date: 29 May 1996 Occurrence class: Operational 
Report status: Final Occurrence category: Accident 
Aircraft details
Aircraft manufacturer: Piper Aircraft Corp 
Aircraft model: PA-60-602P 
Aircraft registration: VH-XRD 
Sector: Piston 
Damage to aircraft: Substantial 
Departure point:Archerfield QLD
Destination:Redcliffe QLD
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Last update 23 July 2015