By Tim Hepher

PARIS, July 20 (Reuters) - Planemaker Airbus <EAD.PA> <EAD.DE> said on Friday that the type of aircraft involved in Tuesday's air crash in Sao Paulo can fly for up to 10 days with a broken thrust reverser.

Debate over the cause of Brazil's worst air crash has shifted from the slick runway to the aircraft's braking systems after it was disclosed one of the A320 airliner's thrust reversers was not operating at the time of the accident.

Nearly 200 people were killed in the crash.

"The A320 Master Minimum Equipment List approved by the certification authorities stipulates that the aircraft can fly for up to 10 days with a thrust reverser inoperative," said an Airbus spokeswoman at its Toulouse, France, headquarters.

Aviation experts say thrust reversers complement the brakes but are not the aircraft's primary braking system and that it is usually safe to fly without them.

That means reversers are not part of the mandatory features on an aircraft -- known as the "Minimum Equipment List," or MEL.

But the advantage to airlines and pilots is that they reduce wear on brakes and can shorten landing distances when needed. Brakes are among the costliest items to maintain.

"Thrust reversers are considered to be nice to have but are not essential kit," said David Learmount, Operations and Safety Editor at Flight International magazine.

"Thrust reversers are not on the MEL so no rules were broken, said Learmount, who is also a former professional pilot.

But he added: "It is a different issue as to whether it was wise in the conditions that prevailed at the time."

Other analysts stressed that a thrust reverser could have curbed a margin for error already dented by the short runway at Sao Paulo's Congonhas airport, which sits in the middle of South America's largest city.

The lack of a reverser is not likely in itself enough to cause an accident without a series of other adverse factors, such as landing speed, the touchdown point, runway wetness, bad weather and other potential technical problems, said aviation consultant Pierre Condon.

"Every day there are planes flying without thrust reversers. It is not abnormal, although perhaps less the case on an A320," said Condon, a former editor of French aviation magazine Air & Cosmos.

Runway surfaces that are new and as yet ungrooved tend to be more slippery than older ones, Learmount said. The runway that TAM Linhas Aereas <TAMM4.SA><TAM.N> jet skidded off in Sao Paulo had recently been repaved and had not yet been grooved to drain rainwater.

Brazilian aviation authorities say the runway, which has been closed since the crash, complied with safety norms.

"No one is perfect and no pilot lands perfectly, but there are margins that you get from the runway length and thrust reversers," Condon said. "But the pilot had no margin because the runway is not long and there was a missing thrust reverser."

The pilot was familiar with the airport and the runway because he flew the route frequently, the airline has said.

AlertNet news is provided by