The emergency landing on 2 May at Sydney, Australia, of an Ansett Boeing 747-300 is likely to cause Boeing to upgrade to service-bulletin status a 1993 service letter recommending that aileron cable guards and pulley covers be replaced with new material.
The aircraft, leased from Singapore Airlines (SIA), suffered partial loss of aileron control shortly after departure for Japan. The pilot reported that he could turn in only one direction, and that the "lock-out" protection device apparently failed to free the system. The incident is under investigation by the Australian Bureau of Air Safety Investigation.
A piece of broken cable guard had lodged in an aileron pulley on the US-registered aircraft, which had undergone heavy maintenance in Singapore and was on temporary lease to Ansett from SIA.
An airline source says that SIA has experienced a similar problem, and a December 1993 Boeing service-letter bulletin records that, in one such event, the cable guard cracked in service because of installation stresses and contamination with grease. Boeing revised the material used to fabricate the cable guards and pulley covers, and recommends replacement of components with the improved parts "-when replacement is required".
Airline sources say that a service bulletin does not make action compulsory, but airlines are more likely to act on its recommendations.
Source: Flight International
