Safety News

‘New Aging Rule: More detailed inspections lie ahead for operators of the oldest small commercial aircraft flying. The FAA plans to implement new requirements by 2004 for maintenance and inspection programs for transports with more than nine seats.

The changes will include requirements that those transports in commercial service for more than 14 years undergo recurring inspections. The maintenance and inspection of these aircraft also will have to be shifted to a "damage-tolerance" basis from the "fail-safe" basis on which many of the aircraft were built and certificated.

The notice of the rule change, published December 6, 2002, is the FAA’s effort to satisfy a longstanding demand from Congress for more diligent aging aircraft inspections. The touchstone for aging airframe issues is the 1988 accident in which an 18-foot section of the upper fuselage tore lose from an Aloha Airlines 737 at 24,000 feet on a flight to Honolulu, Hawaii. One flight attendant was killed and seven people on Flight 243 were seriously injured. Investigators determined a series of minute cracks around rivets in a lap splice united after a lesser failure essentially unzipped the 737.

That focused the industry’s attention on the phenomenon of "multiple site damage" and the problem of transports flown beyond their intended service lives. (The 737’s design life was 75,000 cycles; the Aloha aircraft had been flown for more than 89,000.)

It also focused public and political attention on the safety of aging airframes. One result was Congress’s insistence, codified in the 1991 Aging Aircraft Safety Act, that the FAA inspect old aircraft at set intervals.

The new rule focuses on smaller transports used in Part 121, 129, and 135 operations. The structural-inspection and corrosion-control programs for "heavy iron" aircraft were overhauled within a couple of years of the Aloha accident. Exempted from the new requirements are single-engine aircraft, multi-engine aircraft with nine or fewer seats, and all aircraft operated solely within Alaska. The rule does not cover aircraft operated in on-demand or cargo-only service under Part 135.

For the multi-engine aircraft covered by the new aging-aircraft requirements, those that have been in service for more than 14 years must undergo an inspection and records review supervised by FAA officials within five years. That inspection must be repeated every seven years thereafter.

For affected aircraft in commercial service more than 24 years, FAA-supervised inspections and records review must be performed within four years and repeated every seven years.

Affected aircraft that have been in commercial service for fewer than 14 years when the rule takes effect on December 8, 2003, the FAA-supervised inspections and records review must be performed no later than five years after the 14th year of commercial service is completed, then repeated every seven years.

The rule gives operators who use segmented maintenance programs the option of working with their FAA principal maintenance inspectors on an alternative means of compliance that satisfies the new requirements without disrupting the segmented schedule.

A key change wrought by the rule is the shift to damage-tolerance inspections. Many older aircraft were designed and certificated–and their maintenance programs predicated–on fail-safe design principles, which basically say that failure of critical structure won’t prevent the safe completion of a flight. That is, if something major breaks, the pilots will still be able to get the aircraft on the ground safely.

The damage-tolerance design concept adopted in the early 1970s is more conservative. It dictates that aircraft structure should fail in a manner that allows the failure to be detected in a scheduled inspection. In general, damage-tolerant designs make the assumption that the defect will be missed in the first two scheduled inspections, and therefore the structure should be robust enough to carry all prescribed loads in a partially failed condition until the third scheduled inspection rolls around.

The design concept logically drives the establishment of more conservative inspection timetables.

To assist in determining the inspection intervals required to comply with the new rule, the FAA took the unusual step of specifying design lives for the affected aircraft. Traditionally, it leaves that determination to the aircraft manufacturers. A sample of the design life goals is presented here.

In issuing the proposed rule, the FAA said, it attempted to adjust inspection intervals to coincide with heavy maintenance visits for the affected aircraft. But those visits may not be thorough enough to satisfy the new requirements, the agency warned operators, and additional areas of an aircraft may have to be opened for FAA inspectors or designees to examine.

The agency is accepting comments on the proposed rule until February 4.