US airlines and aircraft manufacturers would have to equip more than 3,200 passenger jets with safety systems to reduce the potential of fuel tank fire or explosions, according to a Federal Aviation Administration proposal on Monday.

Regulators did not include cargo jets in the plan but the rule will not be finalized until after a four month public comment period, the agency said.

The proposal took nearly a decade to develop and was unveiled a year later than planned. Transportation safety advocates said the agency moved too slowly.

White House budget planners reviewed the measure before it was proposed to assess the cost of installing tank safety systems on new planes or retrofitting models in service. The FAA estimates the industry will spend more than USD$800 million over decades.

If finalized, the rule would affect more than 3,200 new and existing jets with center-wing fuel tanks. Most

 of the aircraft are made by Boeing but planes manufactured by Europe's Airbus are also included.

Airliners covered represent the bulk of the commercial US fleet.

"We're proposing to increase the level of aircraft safety by reducing the potentially explosive ingredient of flammable fuel vapors," said FAA administrator Marion Blakey.

The FAA estimates nine aircraft would be destroyed by tank explosions over the next 50 years if the agency took no action.

Boeing 737s, the most popular commercial plane, would be among the first scheduled for retrofits. The leading option is a newly developed inerting system that renders fuel vapors inflammable by reducing oxygen levels in the tank.

As an alternative, industry can reduce ignition sources, like wiring problems, but the FAA said there is no expectation that these can be eliminated.

Other models scheduled for early action are Airbus A320s and Boeing 747s although the FAA said the proposal mainly affects Boeing aircraft. Boeing 767 and 777 models will also be covered under the seven year retrofit plan.

Airbus's new A380 super jumbo, which is undergoing final tests before delivery, is not affected because it does not have a center fuel tank, the FAA said. Boeing's 787 "Dreamliner" has a fuel tank safety system already built into its design.

Airbus has disputed any suggestion tank safety could be compromised by fuel vapors. Three major incidents underpinning the proposal involved Boeing jets.

Nevertheless, Airbus said it will work with the FAA. Boeing said the company was planning to use its own inerting system on aircraft covered by the rule.

 The Air Transport Association, the main trade group for domestic airlines, said the proposal was consistentwith expectations of major carriers after lengthy consultation.

The proposal stemmed from the July 1995 TWA Flight 800 explosion over the Atlantic. The Boeing 747 broke apart after takeoff from New York, killing all 230 people aboard. Investigators believe a wiring problem triggered a spark that ignited fuel vapors in the jet's center tank.

Two other incidents in Asia in the early 1990s and in 2001 involved 737s and were on the ground.