By Don Phillips and Steven Pearlstein
Washington Post Foreign Service
Sunday, September 6, 1998; Page A01

PEGGY'S COVE, Nova Scotia, Sept. 5—After the pilot told air traffic controllers that "we have to land immediately," Swissair Flight 111 went silent and began a five- to six-minute, 9,700-foot death spiral into the Atlantic Ocean, according to preliminary radio and radar data released today.

Perhaps 10 minutes before the plane lost contact Wednesday night with controllers at the Moncton, New Brunswick, air traffic control center, the pilot reported smoke in the cockpit and began descending toward the Halifax airport. Investigators said it appears that the crew donned oxygen masks as conditions deteriorated.

Investigators also announced the first potential break in their effort to determine why the McDonnell Douglas MD-11 crashed, killing all 229 people aboard, saying they heard today the telltale "ping" from the emergency locator transponder on one of the two "black boxes" -- either the cockpit voice recorder or the flight data recorder.

However, deteriorating seas forced divers to leave the water just as they were pinpointing the source of the signal with hand-held scanners at a depth of about 190 feet.

The fresh insights into the cause of the crash came on a day when several bus loads of mourners made a somber pilgrimage to this coastal village to see where their friends and relatives died.

With some carrying bouquets and others clutching teddy bears provided by the local Red Cross, the mourners held quiet vigils under the watchful eyes of Royal Canadian Mounted Police officers who kept the public and press at a distance.

In briefings by Canadian officials, the families were told that few if any of the victims' bodies had been recovered intact and that it could be weeks before remains are identified and ready to be sent home.

As the mourners looked on, more than 40 vessels, including three frigates, crisscrossed the widening search area while helicopters buzzed overhead and a submarine scoured the ocean floor with sonar.

More than 1,500 people have been mobilized to help with the search and care for the relatives, including dive teams from Vancouver and state police from as far away as Massachusetts.

"They've been magnificent," said Tim Larson of East Hartford, Conn. "We can't thank them enough."

A private service for the friends and relatives was held tonight in Halifax. On Sunday, they are scheduled to visit a nearby military base where they can view some the clothing, passports and personal effects that have been gathered.

Investigators, meanwhile, also began checking maintenance records and interviewing "numerous" witnesses who said they had heard or seen the plane. Investigators did not identify the witnesses, but sources said they included a nearby British Airways crew that heard the radio conversation and agreed that the Swissair crew was probably wearing oxygen masks at the end.

But the release of the transcript of some of the pilot's last words was the most gripping of today's developments.

Vic Gerden, investigator in charge for the Transportation Safety Board of Canada, released a partial radio transcript and map of the plane's ground track that indicated a rapidly deteriorating situation on the plane. For about 10 minutes, the crew appeared to be in control of the plane, and the aircraft appeared to be responding normally.

But at the end, the crew abruptly ended contact, and the plane's radar transponder stopped operating. A silent transponder could mean a number of things, ranging from a loss of electricity to a crew flipping electrical circuit breakers in a desperate trouble-shooting effort.

About 16 minutes before the crash, the pilot radioed controllers: "Swissair 111 heavy is declaring 'Pan Pan Pan' [an international distress signal short of an emergency]. We have smoke in the cockpit, request deviate immediate right turn to a convenient place, I guess Boston."

A controller answered, "Would you prefer to go to Halifax?

The pilot replied, "Affirmative for Swissair 111 . . . prefer Halifax from our position."

At that time, the plane was at 33,000 feet and about 70 nautical miles southwest of Halifax, while Boston was 300 nautical miles behind. The plane began descending at 3,000 feet per minute. At some point before the final transmission, the plane leveled off at about 10,000 feet.

The controller began vectoring the plane toward a landing on Runway 6, an approach from the southwest.

"You've got 30 miles to fly to the [runway] threshold," the controller said.

"We need more than 30 miles," the pilot replied.

"Turn left . . . to lose some altitude," the controller said.

After discussing dumping fuel and making a sweeping 180-degree turn, the situation deteriorated, but the pilot gave no clue what had happened.

"We are declaring an emergency. . . . We are starting to vent now. We have to land immediately," the pilot said.

Gerden said it is unclear whether the pilot meant the crew was venting smoke from the plane, dumping fuel or some other action.

Twice, the controller cleared the crew to dump fuel but received no answer.

About a minute after the last transmission, radar picked up only "primary" radar echoes, indicating loss of the transponder that reports the plane's altitude and identification to controllers.

"This will be a slow one," said one source inside the investigation. The plane went down in at least 150 feet of water, a difficult working area for divers.

However, when the recovery team finds the recorders, the investigation could proceed rapidly because of the sophistication of the data recorder that measures numerous aircraft movements and records dozens of aircraft systems and control inputs.

Kurt Bruehwiler, Swissair's division manager of line maintenance, said in an interview that the data recorder has 140 channels, far more than older varieties in service.

However, a source close to the investigation pointed out that the plane's radar transponder stopped working at 9,700 feet. If the plane's electrical systems shut down at that point, the recorders also would shut down and would not record the plane's last plunge.

The investigation also is continuing in the United States and elsewhere.

The FBI and the Federal Aviation Administration are tracing every cargo shipment on the aircraft but so far have found nothing to indicate the presence of hazardous material or flammables. Determining whether illegal hazardous material or contraband was aboard will be more difficult and must await the detailed analysis of the investigation.

However, Bill Savage, Swissair's cargo sales and service manager in New York, said in an interview that Swissair cargo is unlikely to contain illegal material because the airline works almost exclusively with established shippers who are well known to both the airline and the FAA.

Tragically, the brother of one crash victim died on another Swissair flight today. The man, whom Swissair would not identify, complained of medical problems shortly after Flight 125 left Chicago for Zurich Friday night. The plane landed at Toronto as two doctors on board tended to the man. He had been returning to Zurich to console other members of the crash victim's family.