Report by NTSB on a similar incident on an A320: https://www.ntsb.gov/ntsb/brief2.asp?ev_id=20001205X00227&ntsbno=NYC99IA062&akey=1 which in part reads: BEGIN QUOTE Documents from Airbus indicated there have been three similar incidents in which A320 airplanes landed with the nose wheels rotated about 90 degrees. Examination of the steering control modules on two of the airplanes revealed extrusion of the selector valve's external seals similar to that found on N628AW. Airbus had attributed the extrusion failures to the lack of a backup seal or the effects of aging on the seals. As a result of these incidents, Airbus issued Service Bulletin (SB) A320-32-1197 on October 8, 1998, to recommend replacement of the external seals on the steering control module's selector valve on A320 and A321 airplanes within 18 months of the SB's issuance. At the time of the incident, neither the French Direction General de l'Aviation Civile (DGAC), or the Federal Aviation Administration (FAA), had adopted the service bulletin as an airworthiness directive. The operator was not required to comply with the service bulletin, and had not complied with it. On March 24, 1999, the DGAC issued Airworthiness Directive (AD) 1999-124-129(B) to require compliance with the SB. On December 17, 1999, the FAA issued AD 99-23-09 which was based upon the French AD, with a 12 month time of compliance for modification of the nose wheel steering control valve. END QUOTE If I read this correctly, the AD's require the seals to be replaced just once (on all the airplanes flying at the time of the directive?). Maybe it says every eighteen months? Kind of puzzling. Gerry http://www.pbase.com/gfoley9999/ http://www.wilowud.net/ http://home.columbus.rr.com/gfoley http://www.fortunecity.com/victorian/pollock/263/egypt/egypt.html