The 78-minute tape indicated the signal-boosting repeater used to amplify and retransmit radio signals did, in fact, effectively pass transmissions on Sept. 11, 2001, The New York Times reported in its Saturday editions.

The finding contradicts an earlier emergency response study which was endorsed by Mayor Michael Bloomberg and Fire Commissioner Nicholas Scoppetta.

That study attributed part of the problem to the destruction of a signal-boosting repeater in the attack. The repeater was mounted atop neighboring 5 World Trade Center to amplify and retransmit radio signals, and was destroyed when the first tower collapsed.

Although very few communications from the north tower are heard on the tape, the Port Authority said that firefighters in the south tower can be heard speaking over their radios until the building falls, indicating that the system worked.

The new analysis raises the possibility that other factors, including human error and other equipment failures, might have triggered the communications breakdown believed to have contributed to the deaths of 343 firefighters.

Officials at the Port Authority, which was responsible for the equipment, have maintained that complaints about the communications system they installed have been used to deflect blame.