The Australian Transport Safety Bureau (ATSB) plans to release a report next year on the validity of the usage spectrum assumptions that were used for certification of the Robinson R22 helicopter.
The study follows the investigation of a number of R22 main rotor blade separation incidents, including the June 2003 crash of an R22 on a training flight at Bankstown, Sydney.
That helicopter suffered a main rotor blade separation due to a fatigue crack before it reached its mandatory time in service life.
Since that incident, and a similar one in Israel, Robinson has introduced a redesigned main rotor blade, revised retirement lives for the blades, amended maintenance manuals and published safety alerts. Australia’s Civil Aviation Safety Authority has drafted a notice of proposed rulemaking, which will require the retirement of earlier rotor blades by 1 March 2006 on Australian-registered R22s.
The European Aviation Safety Agency issued an airworthiness directive in July mandating main rotor blades on the European fleet be replaced with the redesigned blades by 1 December.
Last week the ATSB published its final report into the June 2003 crash, which resulted in the death of the two occupants. The main rotor blade failed due to fatigue crack growth in the blade root fitting. The fatigue failure was in a similar position to failures found in two previous accidents in Australia, although both of these were linked to under-recording of hours. Adhesive disbonding between the main rotor blade skin and blade root fitting found on the Bankstown R22 was subsequently discovered on a number of other main rotor blades that had not reached retirement age.
The Bankstown R22, with 2,055h in service and 11 years and eight months calendar life, had not exceeded its 2,200h mandatory time in service life or 12 year calendar time in service life.
As a result of its investigation, the ATSB is researching the usage spectrum of an R22 used for cattle mustering in the north of Australia – a popular role for R22s in the country. The ATSB intends to compare the actual usage spectrum with the assumed usage spectrum that was used for certification in order to assess some of the structural and maintenance control assumptions on which the airframe integrity is based.
EMMA KELLY/PERTH
Source: Flight International
