US passenger and cargo airlines on Tuesday sought to stop, or at least change, a Federal Aviation Administration proposal to overhaul management of structural fatigue in older aircraft.

The biggest passenger carriers and their cargo counterparts said the agency's proposal last April was premature and incomplete.

They also said the FAA significantly underestimated what it would cost the airlines in maintenance and aircraft retirement costs to comply with the regulation.

"Unfortunately, the proposed rule is quite simply unjustified. It should not be made final," the industry's primary trade group, the Air Transport Association, said in documents filed with the Transportation Department.

For the first time, the FAA proposed strict criteria for determining life limits for commercial aircraft, potentially affecting thousands of aircraft currently in service.

The plan would also push new costs -- at least USD$360 million over 20 years -- onto an industry with several carriers that fly many older planes, the FAA said.

Manufacturers, such as Boeing and Airbus, would pick up about 10 percent of the cost while airlines would pay the rest. But industry estimates costs in excess of USD$3 billion, if certain scenarios involving aircraft retirements were considered.

FedEx said the proposal was overly complex and would "drain resources."

Regulators say airlines would save hundreds of millions of dollars in maintenance and other costs, if the rule was put in place as written.

Carriers say most current practices are adequate and any changes must be carefully considered.

A House of Representatives aviation subcommittee hearing on FAA safety programs is scheduled for Wednesday.

Currently, manufacturers must determine an expected aircraft life and show serious fatigue damage will not occur in new designs. There is no rule limiting operation once a plane exceeds its estimated life and fatigue becomes a concern.

Boeing says its planes are built to be commercially viable for 25 years, but can be flown longer if they satisfy airworthiness regulations.

Many big older planes have minor cracks caused by physical changes related to cabin pressure differences and are repaired. Small cracks can occur in an aircraft's skin or on structural parts such as frames and spread to different areas.

Fatigue issues received closer attention in 1988 when a section of upper fuselage on an Aloha Airlines 737 peeled up during flight. A flight attendant was sucked out of the aircraft. The plane landed safely.

FAA then stepped up fatigue inspections, corrosion prevention and repairs to reduce the number of repetitive checks. But those programs do not address the most serious type of fatigue damage.