Questions about the radio system used by the Fire Department during the World Trade Center terror attacks are being raised anew by the 9/11 commission, which has grilled a hero FDNY chief whose brother died when the buildings crumbled.
Commission staffers in recent weeks asked Deputy Chief Joseph Pfeifer why he did not use the critical Channel 7 frequency on the Motorola "handie talkies" in favor of another channel on the morning of Sept. 11, 2001.
Channel 7 was the only radio channel capable of transmitting messages from commanders in the Twin Towers' lobbies to firefighters on the upper floors. The channel used a signal booster - a "repeater" - located on the roof of 5 World Trade Center.
Commission investigators learned Pfeifer switched frequencies when they were listening to a 78-minute recording of FDNY radio chatter at the trade center that showed the repeater and radios worked.
The FDNY says problems with the repeater and the digital Motorola radios prevented up to 121 firefighters in the north tower from hearing evacuation orders given an hour before the building collapsed.
Results of the commission probe into the city's handling of the terror attacks will be aired next Tuesday and Wednesday when members hold hearings at the New School for Social Research in Greenwich Village - where commission member Bob Kerrey is president.
The commission is also questioning why Pfeifer allowed a civilian Port Authority employee to initially turn on the repeater control console.
Investigators are trying to determine whether having a civilian set up the repeater for operation may have been a factor in difficulties Pfeifer says he later experienced trying to use it.
Pfeifer also said there was nothing unusual about him asking a Port Authority employee to initially operate the repeater.
"That happens all the time," he said. "It's the Port Authority's building, and I asked them to turn the repeater on."
Pfeifer, 48, was the first battalion chief to arrive at the north tower after the 8:48 a.m. attack and was responsible for setting up communications.
He tested radio transmission on Channel 7 with Battalion Chief Orio Palmer, who was also in the lobby of the north tower, but the two could not hear each other, FDNY spokesman Francis Gribbon said.
Pfeifer sent an aide to try a portable repeater kept in his vehicle but found that did not work, either. He then switched to Channel 2 to confer with other brass, while using Channel 1 to address responding units, Gribbon said.
Both those frequencies were capable of reaching about five floors, said retired FDNY Chief Albert Turi, who was questioned by probers three weeks ago.
"Channel 7 would be the one we had to listen to to hear transmissions coming through the repeater system," Turi said.
After Pfeifer gave up on Channel 7, firefighters were ordered to switch their radios to Channel 2, which became the command channel.
One result was many firefighters struggling to rescue office workers in the north tower had no idea the south tower was hit by a second jet at 9:03 a.m.
When the south tower was struck, Palmer moved to the lobby in that tower and found out the repeater and radios worked when he was able to speak with firefighters as high up as the 78th floor, Gribbon said.
Those exchanges were recorded by the repeater, along with the test conversations between Palmer and Pfeifer.
At 9:28 a.m., Chief Joseph Callan, who had relieved Pfeifer, broadcast on the two radio channels in use orders that firefighters leave the north tower.
"Everyone come down out of the building. Leave the building immediately," Callan said, according to an interview he gave retired FDNY Chief Vincent Dunn.
But few in the north tower heard his order - and when the building collapsed an hour later, Pfeifer's brother, Kevin, was among the dead.