Some operators of Twin Commander 690A/B model twin turboprop business aircraft have been given a reprieve from being compelled to carry out immediate repair work in the area of the type's rear pressure bulkhead.

The Federal Aviation Administration airworthiness directive AD 2013-09-05, issued in May, required detailed modification work to be carried out on the area. However, the FAA and support company Twin Commander Aircraft have now agreed that although the requirement for inspection remains immediate, if on inspection no cracks are found the aircraft may continue to fly for another 100 flights or 110 flight hours, whichever comes first, before the work must be carried out.

Twin Commander president Matt Isley said: “This will give operators who are facing a busy flying season a reprieve. Given the number of aircraft affected by the AD, it will also allow some operators an option to continue flying as they wait for an inspection slot to open up at a qualified maintenance center.” The company explained that the required modification first entails installation of a thicker-gauge upper window channel, but inspections can be conducted up to three times - provided no cracking is found - before the full service bulletin (SB241) inspection and modification must be performed.

The problem for this out-of-production - but still popular - business aircraft type was discovered three years ago during routine inspection, and Twin Commander Aircraft issued SB241 in September 2012, resulting in the AD. “These cracks developed over time due to wing loads and pressure cycle stresses concentrating in a single area on the aircraft,” Isley said. “Thus the need for a service bulletin to inspect the affected area, and make necessary modifications so that no further inspections will be required.”

Isley warned: "Although the FAA’s AD note does not require it, it is extremely important that operators use those maintenance facilities that have received the proper factory training to perform this work. The modification work is complex and there is potential for damage and costly corrective repairs if the work is performed improperly.”

Source: Flight International