Twin Commander Eases Bulkhead AD Compliance

 - October 9, 2013, 10:20 AM
A modified thicker-gauge upper window channel must be installed before Twin Commander operators can take advantage of a procedure that allows them to delay compliance with a recent airworthiness directive.

Twin Commander Aircraft and its authorized service centers are responding to accommodate owners and operators affected by a recent airworthiness directive calling for inspection and modification of the aft pressure-bulkhead area.

Twin Commander proposed, and the FAA recently approved, a procedure that provides some operators relief from the strict compliance requirements in AD 2013-09-05, which is based on Service Bulletin (SB) 241.

The revision to SB241 allows operators to perform an inspection of the aft pressure-bulkhead area, and if the inspection does not reveal cracking, the operator will be able to resume flying for another 100 flights or 110 flight hours, whichever comes first. This procedure may be repeated two more times before implementation of the AD is required. The procedure does require that a modified thicker-gauge upper window channel be installed first.

Matt Isley, Twin Commander Aircraft’s president, said installation of the thicker upper window channel takes about six days, costs approximately $10,000 and can be performed by a qualified technician. The inspection itself takes about a week and can be done concurrent with the replacement of the upper window channel.

“The determination of the allowable flight hours and number of flights is based upon crack growth analysis. If you check it today and tomorrow a crack begins, the question is how long it will take that crack to grow to the point it becomes a problem. The analysis indicates it would take five times longer than [the time period] we’ve recommended, so there is a significant safety buffer. However, the engineering analysis is based upon installation of the thicker upper window channel to brace the section above and below the picture window. The upper window channel distributes the load that would otherwise be concentrated in the aft pressure bulkhead,” Isley told AIN.

“This procedure is of particular value to those operators who can’t afford to wait to get a slot in maintenance for the fix. For instance, seasonal operators for whom the bulk of their work is occurring now need to be able to keep that airplane in the air,” Isley said.

To date about 110 aircraft have been modified; approximately 440 active aircraft are affected by the AD, and about half of them are based in the U.S.