Fielding a SHM System for an Aged Military Aircraft

Abstract

Aging military aircraft require an increasing amount of structural inspections to safely maintain them. In a case with Norwegian Defence Sea King search and rescue helicopters, required X-ray and Eddy Current inspections on two of the Main Gearbox Attachment Lugs threatened to ground the fleet. The lugs are made of casted aluminum and subsequently have a very short critical crack length. After extending the use of the helicopters beyond its safe life of 10000 flight hours, crack lengths became critical faster than the OEM recommended inspection intervals. The SMART layer sensor network was installed on the remaining fleet of helicopters while they were in for heavy maintenance. With the help of hardware for data acquisition and analyzing software, the RNoAF technicians have been able to inspect the cracks at short intervals. Acellent have verified the data integrity and reported crack status. With the Acellent SHM system installed in the remaining active fleet of Sea Kings, the following requirements where adhered to: • The installation did not need any certification • The sensors did not cover the damaged area • Time used for inspection is well beyond 10 minutes • The installation did not require any design changes • Applying the sensors did not increase normal depot downtime.