16 July 2001
Tail rotor pitch change spider
A recent crash of a British registered AS 355F2 has been attributed to the in-flight disruption of the spider bearing which is part of the tail rotor hub pitch change assembly.
Manufacturer's Service Bulletin (SB) 65.00.15 (Modification 076551), applicable to the AS 355 series, was carried out by a line maintenance mechanic only 20 flying hours prior to the crash.
Instructions in this SB required that the housing be heated to 80°C before insertion of the bearing. This is to reduce the slight interference fit and to minimize the risk of damage to the anti-fretting varnish on the bore of the housing as the bearing is installed. Discussion with the engineers who had installed the new bearing stated that this procedure had been carried out using an uncalibrated domestic oven.
Subsequent to the above, the UK CAA has unilaterally issued a CAA Letter to Affected Owners and Operators. The letter specified that SB 65.00.15 should only be embodied by a maintenance organization with an appropriate component rating (i.e. JAR 145) with the subject pitch change spider included on their capability list, and to be undertaken only if all necessary tooling, including a calibrated oven and a suitable press, are available.
Transport Canada shares the UK CAA concerns and has asked the DGAC (France) who would best accomplish replacement of the pitch change spider bearing as per SB 65.00.15. Transport Canada similarly questioned the DGAC about SB 65.00.38 which is applicable to the AS 350 series rotorcraft.
Because replacement of the spider bearing must be carried out in a very precise and sequential manner, Transport Canada strongly recommends that engineers be extra vigilant when accomplishing these SBs, and that they use a calibrated oven equipped with a temperature control unit and a temperature indicator.
Any defects or further occurrences should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.
For further information, contact a Transport Canada Centre, or Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone (613) 952-4358, facsimile (613) 996-9178 or e-mail email@example.com.
For Director, Aircraft Certification
Chief, Continuing Airworthiness