Transport aircraft receiving repairs or alterations to any fatigue critical structure (FCS) must undergo a damage tolerance evaluation (DTE), setting out how the structure must be monitored and maintained for years to come. The DTEs occur for good reason – a tragic 1988 incident where a roof section unzipped from an Aloha Airlines 737 helped spur the FAA requirement – but can be challenging for airlines and others responsible for obtaining them.
A partner with expertise in diverse aircraft types, their components, fatigue assessment, operations, maintenance procedures and FAA compliance can perform the evaluations cost-effectively and expeditiously so fleet operations are not unnecessarily disrupted.
The wings and the skin, ribs and stringers of a fuselage are just a few of the primary structures that can be designated fatigue critical, because their failure would affect the airworthiness of the aircraft. On some aircraft, secondary structures such as an engine cowling hinge are considered fatigue critical as well, because if the hinge failed, the cowling could fly off and hit a horizontal stabilizer or other part and affect the plane’s airworthiness.
When those structures undergo repair under Part 25 of FAA regulations, a damage tolerance evaluation must be performed within 12 months of the return to service. The DTE, required under Part 26, looks at the materials and the stress they’ll undergo and sets out maintenance procedures. If fatigue inspections are required, their intervals and the method of inspection are set out in a damage tolerance inspection (DTI) document.
Alterations are another common occurrence triggering a damage tolerance evaluation, which must be performed before the modification is certified and the aircraft can return to the air. In some cases, the provider performing the alteration – say installing cabin communications systems on a fleet – is charged with obtaining the DTEs on behalf of the certificate holder, the airline. The alterations, too, can generate fatigue-related damage or affect additional critical structures, bringing the requirement for more DTEs.
SeaTec’s engineering services team has years of expertise with manufacturers, major airlines and technical operations that equip us to perform damage tolerance evaluations.
With each DTE, our engineers examine how the repair or alteration was performed, look at the materials involved and then conduct a fatigue and damage tolerance analysis using industry-recognized methodology and conservative assumptions. Based on the findings, the customer receives:
- An instruction for continued airworthiness (ICA) report detailing new or adjusted inspections.
- An FAA Form 8110-3 signed by the designated engineering representative, confirming approval of the evaluation and recommended inspection processes.
Whether a one-off evaluation for a repair or multiple DTEs involving modifications, the SeaTec team tailors its process and turnaround times to meet the operator’s schedule, knowing from experience that time on the ground is revenue lost.
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