irworthiness Directive 2009-25-02, requiring owners of 690, 690A and 690B Twin Commanders (with the exception of six serial number-specific aircraft) to have their aircraft inspected for corrosion between the upper wing skin panels and engine mount beam support straps. The inspection must be performed within
the next 150 hours time in service beginning January 8, or by Jan. 8, 2011, whichever comes first.
According to a spokesman for the company, many of the aircraft in the fleet have already been inspected and modified, but approximately 270 have yet to comply with the directive. Twin Commander Aircraft has been gearing up for the required inspection by preparing
the necessary replacement parts kits.
“We’re cautioning operators who have not yet complied that prolonged delay might result in failure to meet the compliance date requirement as a limited number of authorized personnel try to service a large number of aircraft,” he said.
Authorized service centers have been preparing by alerting customers of the impending airworthiness directive and sending technicians to special training at FlightSafety International. The company has stipulated that the work be performed by technicians who have completed FSI’s SB237 course because of the complexity and critical nature of the work and inspection.
The AD is based on Twin Commander Alert Service Bulletin 237, which describes an inspection process that calls for removal of the upper engine nacelles to expose
the engine mount beam support straps and removal of the straps to inspect for corrosion on the exposed upper wing skins.
At a minimum, the steel engine mount beam support straps must be replaced with new straps providing better corrosion protection. If corrosion is found, the upper wing skins must be replaced. The service bulletin allows for various replacement options, depending on the extent of corrosion. Different options can be used
on right and left wings.