Wednesday, September 8, 2010

Aging Aircraft Safety Rule Deadline, Fatigue-Critical Structures & ASIG

Welcome to Wired!

In medicine, the guiding principle is “First, Do No Harm.” In other words, treating the malady is not supposed to adversely  affect the patient’s immediate health or long-term quality of life.

737 Convertable A similar rule will soon affect Part 121 and 129 operators. At the heart of the Aging Aircraft Safety Rule (AASR) is the requirement that the repair, alteration, or modification of fatigue-critical structures does not affect airframe integrity and safety. To ensure this outcome, by December 20, 2010, operators must have in place a maintenance program based on the airframe’s damage tolerance.

“Aging,” however, is a misnomer. AASR affects every US-registered airplane in 121/129 service that was delivered before the December 20, 2010 deadline. Whether you’re flying a venerable DC-8 or a 777 that was delivered yesterday, AASR applies to you. At best guess, it affects roughly 4,000 airplanes and 240 operators. (That number could more than double if Transport Canada and EASA decide to adopt its requirements.)

In the FAA dictionary, a fatigue-critical structure “is susceptible to fatigue cracking that could contribute to a catastrophic failure.” This includes structures that become susceptible to catastrophic fatigue cracking due to alteration or repair.

ASIG has built considerable knowledge of and experience with  AASR requirements and processes through years of STC work.  Since  January 11, 2008, the rule has required that STCs include damage tolerance inspections of fatigue-critical structures. It has made the same requirements for new or revised repair and master-change service bulletins. The point is that regardless of how the information is delivered, STC or service bulletin, the essential process for acquiring the necessary data is the same.

 Advisory Circular 120-93, Damage Tolerance Inspections for  Repairs and Alterations, provides the necessary guidance. To comply, by December 20 operators must reassess their structural maintenance programs and how they handle repair approvals. They must survey all active airplanes and document what existing  repairs, alterations, and modifications require damage tolerance inspections. Compliance might sound easy, but it requires complex process and procedural changes and revisions to existing maintenance programs.

In the FAA dictionary, an “existing” repair, alteration, or modification will have been performed before December 20, 2010 on a fatigue-critical structure not already covered by a damage tolerance evaluation and resulting inspections.

B727 The survey and evaluation process starts with an “as-delivered” aircraft, with  OEM supplied documents setting the baseline.  These documents define and list fatigue-critical structures and include updated damage-tolerance maintenance data in repair manuals and in  fleet and master-change service bulletins. STC holders, such as ASIG, provide baseline data for applicable modifications.

The Operator Implementation Plan (OIP) is built on the foundation of baseline data. It includes a timeline for such milestones as completing the fleet survey, determination of damage tolerance inspections, and accomplishment of those first inspections. The OIP is due by December 20, 2010, and the operator’s FAA principal maintenance inspector must review and approve it.  ASIG’s leadership team has its foundation in air carrier engineering management.  Their efforts have led to the derivation of a variety of FAA accepted procedural compliance programs supporting airframe “thumb-printing,” specifically those tracking, detailing and analyzing damage tolerance.   Damage tolerance programming and DTA show-compliance determinations are at the very core of ASIG’s Structural DER cadre.

Once the OIP and the individual airframe applications are approved, the work continues after the deadline as operators follow their OIP to compile their damage tolerance data and revise their maintenance programs that sustain fatigue-critical structures and airframe integrity.

ASIG extends its sincere thanks to thanks to Mr. Mike Gray of Sun Country Airlines for suggesting we address this industry critical topic.

Until next time, stay 5x5, mission ready, and Wired!