By Todd Benson

SAO PAULO, July 19 (Reuters) - Debate over the cause of Brazil's worst air crash began to shift on Thursday from widespread claims of a faulty runway to potential pilot error or mechanical failures.

Since Tuesday's fiery accident at Sao Paulo's Congonhas airport that killed around 200 people, many officials and aviation experts have focused on the rain-soaked runway that the plane skidded off before slamming into a gas station and cargo terminal.

But a video of the botched landing of the Airbus <EAD.PA> A320 released by the national airport authority suggests other factors were also at play in Brazil's second major aviation disaster in less than a year.

The footage appears to show the TAM Linhas Aereas <TAMM4.SA><TAM.N> plane accelerating instead of braking when it touched down on the short, slippery runway -- perhaps because the pilot was trying to lift off again.

"The government is clearly trying to convince public opinion that the runway at Congonhas was not at fault," said Elnio Borges, president of the Varig Pilots' Association. "They're going to do everything they can to blame the pilot."

Officials estimate up to 200 people were killed in the crash, including casualties on the ground and all 186 passengers and crew on board.

By Thursday afternoon, firefighters had pulled 181 charred bodies from the smoldering wreckage.

Four badly injured victims have died in hospital, bringing the official toll to 185. At the TAM cargo building hit by the plane, as many as five employees were still missing.

SAFETY CONCERNS

The crash highlighted long-standing safety concerns about Sao Paulo's aging domestic airport. Congonhas, which sits in the middle of South America's largest city, is known for its short and slick runways.

The TAM plane was trying to touch down on a surface that had been repaved in June after officials tried to ban large jets over fears they could skid off the short landing strip.

But the runway still had not been grooved to drain rainwater, prompting criticism that the airport was reopened prematurely because it is so important to Brazil's economy.

"The real question is why was Congonhas reopened in that state," said Paulo Sampaio, an aviation consultant at Multiplan Consultora in Rio de Janeiro. "It's a crime."

The airport resumed operations on Wednesday with an alternate runway. But federal prosecutors filed a petition to have it shut until both runways were determined to be in line with safety standards.

The video of the landing seems to cast doubt on whether the runway was at fault. It shows the plane speeding up after touching down very close to the designated limit for landings and suggests the pilot tried to take off again after realizing he could not brake in time.

"It's evident that something went wrong that didn't allow him to slow down in time," said Jose Carlos Pereira, president of the national airport authority.

"We have to clarify why the plane accelerated again," he added. "But only the black box can tell us that."

Firefighters have already recovered one of the plane's two cockpit recorders, which will be sent to the United States for analysis. French and U.S. safety investigators are helping Brazilian authorities probing the cause of the crash.

Air travel in Brazil has been chaotic since a Boeing 737 <BA.N> clipped wings in mid-air with a private jet last September and crashed in the Amazon jungle, killing 154 people.

Air traffic controllers, fearing they were being made scapegoats for that accident, have staged periodic work slowdowns to protest against deficient radar and radio equipment.

Delays and cancellations have become routine, prompting frustrated passengers to occasionally storm onto airfields. (Additional reporting by Denise Luna and Claudia Pires)

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