The AAIB's key findings include
15. During the investigation, other instances of cracking on the original standard of clevis lugs, associated non-approved welded patch repair, and a non-approved welding repair of the outboard flange area were found on other Hughes 269 helicopters in the UK, indicating that the non-approved welding repair found on G-ZAPS was not an isolated occurrence on this helicopter type.
16. Hughes Helicopters had previously responded to the cracking problem on the clevis lugs of these centre frame rear cluster fittings with additional periodic inspections and a re-designed –3 type of cluster fitting, but it became apparent during this investigation that there was confusion within UK personnel responsible for the maintenance of Hughes 269 helicopters regarding the difference between the original and re-designed -3 standards of these centre frame cluster fittings, and which inspections applied to which standard of fitting.
17. Six previous accidents to this type of helicopter were identified which had been caused by fatigue failure of clevis lugs on the original standard of centre frame rear cluster fitting; all six accidents had stemmed from fatigue cracking of the left clevis lugs. In addition, one fatal accident had occurred in Australia in 1995 due to fatigue failure of an upper clevis lug on a re-designed -3 centre frame rear cluster fitting. No previous accidents were identified which had occurred due to failure of a clevis lug that had been weld-repaired.
18. This accident, and those which had also occurred previously due to fatigue failure of these clevis lugs on helicopters of this type, demonstrated that such clevis lug fatigue cracking could remain undetected, despite frequent opportunities and requirements for in service inspections of these readily viewed fittings, until eventual failure of such weakened lugs caused accidents. Such findings questioned the regulatory reliance placed upon such inspections to detect fatigue damage of these clevis lugs before catastrophic tailboom separation occurred.
19. A lack of logical standardisation was apparent with respect to the timespans that maintenance records and associated documentation must be kept by aircraft operators and maintenance organisations. The ANO requires operators to retain aircraft Log Books for two years after related aircraft have been permanently withdrawn from service, but JAR 145.55 only requires maintenance organisations to retain work records for a minimum of two years after the aircraft to which they refer have been released on completion of related maintenance work. In effect, the potential advantages to investigations of retaining Log Books for the life of an aircraft can thus be nullified by the absence of the detailed maintenance records to which the Log Books refer, if the related work of interest has been completed more than two years before an aircraft suffers a maintenance related accident.
and
4. Safety Recommendations
The following safety recommendations were made during the course of the investigation:
4.1 Safety Recommendation No 2001-80 The CAA should forward an information notice to all Licensed Aircraft Engineers, and all approved aircraft and component maintenance organisations, reminding them of the requirement that all repairs, including weld repairs, can only be carried out to an approved repair scheme and of their responsibilities to ensure that there is an appropriate repair scheme in the manufacturer’s maintenance or repair manual, or related approval is granted by the manufacturer, before any repair is authorised.
4.2 Safety Recommendation No 2001-81 The CAA should tighten the approval process for persons granted CAA Welders Approval Certificates to ensure that before they carry out any welding repairs to aircraft or aircraft components, written assurance is obtained from the authorising Licensed Aircraft Engineer that such repairs are in accordance with an approved repair scheme.
4.3 Safety Recommendation No 2001-82 The CAA should take early action to introduce a requirement that Welding Certificates of Conformity must state details of the applicable aircraft registration, type, component, part number, serial number and approval for the related weld repair.
4.4 Safety Recommendation No 2001-83 The CAA should remind all Licensed Aircraft Engineers and aircraft maintenance organisations that maintenance should not be undertaken on aircraft without access to the associated Log Books and Technical Log (if applicable) and that all work should be recorded as required.
4.5 Safety Recommendation No 2001-84 In order to better justify assumed airworthiness assurance arising from CAA Survey Reports the CAA should require, before any aircraft or helicopter is surveyed by a CAA Surveyor for the purpose of issuing a Survey Report, that the service history of the type be carefully audited by the Surveyor to identify any critical structural areas which have been the subject of special inspections / Airworthiness Directives to ensure that such areas are closely inspected, if reasonably accessible, during these surveys.
4.6 Safety Recommendation No 2001-85 The CAA should specify who is authorised to carry out and certify a Daily Inspection (A Check), in addition to describing the initial training and continuity training required for such authorised persons, how that training should be recorded and monitored, and where the authorised person should sign to certify that a Daily Inspection (A Check) has been carried out satisfactorily.
4.7 Safety Recommendation No 2001-86 The CAA should require that all pilots use a Pre-Flight Check List from the CAA approved Pilot’s Flight Manual whenever a flight is conducted for training, conversion or testing so that only approved and fully amended Check Lists are used.
4.8 Safety Recommendation No 2001-87 The Schweizer Aircraft Corporation should amend the Pre-Flight Check List contained within the Pilot’s Flight Manual for the Hughes/Schweizer 269 and 300 helicopters to include in the Pre-Flight Inspection a visual check of the right centre frame rear cluster fitting for cracks and damage, and to include the warning that if cracking of cluster fittings is suspected then dye penetrant inspection is required before flight.
4.9 Safety Recommendation No 2001-41 In view of the finding of non-approved welding repairs to the clevis lugs of the Centre Frame Rear Cluster Fittings on two Hughes 269 helicopters, failure of one of which caused a catastrophic in-flight separation of the tailboom assembly, it is recommended that the Civil Aviation Authority and the Federal Aviation Administration take early action to issue Airworthiness Directives to require immediate visual inspections of these fittings on all Hughes/Schweizer 269 and 300 helicopters in order to check for any non-approved welded repairs to the clevis lugs, and to ground any affected helicopters until such repaired Centre Frame Rear Cluster Fittings have been replaced with new fittings. (Safety Recommendation No 2001-41, made 11 April 2001)
4.10 Safety Recommendation No 2001-45 In view of the potential for catastrophic in flight tailboom detachment on Hughes/Schweizer 269 and 300 helicopters due to fatigue fracture of the clevis lug attachments on the Centre Frame Rear Cluster Fittings, and the difficulty in reliably detecting by dye-penetrant testing all such fatigue cracking in service before related lug fracture occurs, it is recommended that the Civil Aviation Authority issues an Airworthiness Directive requiring the mandatory replacement, on all affected helicopters of these types on the UK Register, of all original Centre Frame Rear Cluster Fittings, part numbers 269A2234 and 269A2235, with the manufacturer's re-designed Cluster Fittings, part numbers 269A2234-3 and 269A2235-3; it is further recommended that the Federal Aviation Administration should implement similar mandatory modification action for all affected helicopters of these types abroad. (Safety Recommendation No 2001-45, made 11 April 2001).
4.11 Safety Recommendation No 2001-88 The CAA should conduct a review of JAR 145.55 with the aim of proposing to the JAA the improved harmonisation of maintenance document retention time requirements with those specified in the ANO, so that maintenance Worksheets and component Certificates of Release that are referred to in Aircraft, Engine and Propeller Log Books are retained until the aircraft, engine or propeller has been destroyed or scrapped.
4.12 Safety Recommendation No 2001-89 In order to avoid inadvertent omission of manufacturer’s inspections during maintenance, it is recommended that the CAA withdraw the option to use the generalised CAA Light Aircraft Maintenance Schedule for Hughes/Schweizer 269 and 300 series helicopters so that they may only be maintained to the manufacturer's Handbook of Maintenance Instructions (HMI).
4.13 Safety Recommendation No 2001-90 The CAA should conduct a review of the manufacturer’s maintenance manual requirements for all helicopter types on the UK register which are currently maintained to CAA/LAMS/H/1999 issue 1 and where there are significant additional ‘specific-to-type’ maintenance requirements in the applicable maintenance manuals, require such helicopters to be maintained only to the manufacturer’s maintenance manual.
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Tudor Owen