PORT HUENEME, Calif. - One of the ``black boxes'' aboard Alaska Airlines Flight 261 recorded a loud noise in the minutes before the MD-83 went out of control and plunged into the ocean, a federal investigator said Friday.
The noise was one of two revealed by analysis of the cockpit voice recorder, said John Hammerschmidt, a member of the National Transportation Safety Board.
The tape revealed new details of what occurred on the doomed flight in its last minutes as the pilots struggled to control a problem with the horizontal stabilizer - the part of the tail that controls up and down pitch of the plane. The plane nose-dived into the Pacific Ocean en route from Puerto Vallarta, Mexico, to San Francisco on Monday, killing all 88 aboard.
About 12 minutes before the end of the recording the plane apparently lost vertical control, Hammerschmidt said.
The crew recovered control in about 1 minutes. Then a flight attendent is heard telling the pilots she heard a loud noise from the rear of the jet.
``The crew acknowledged that they had heard it too,'' he said.
``Slightly more than one minute before the end of the recording, a loud noise can be heard on the recording and the airplane appears to go out of control.''
The plane has an audible alarm to indicate a stall, or dangerous loss of lift. No such warning is heard on the tape, Hammerschmidt said.
He said the investigation was progressing rapidly, including work at sea by a Navy vessel using side-scan sonar to map debris in the Santa Barbara Channel.
Sonar appeared to show the debris in a single concentration within an area the size of a football field, and the survey was continuing one mile out in each direction, he said.
Some of the debris has been videotaped by a remote-operated underwater vehicle. Most of the debris examined so far in pieces about 5 feet or 6 feet long, but there was a section of fuselage estimated to be 10 feet long.
The submersible has sent up video of the tail and all-important horizontal stabilizer, including a 5-foot section of the leading edge of the stablizer, and a piece of the skin of the vertical stabilizer about 5 feet to 7 feet in size, Hammerschmidt said. The horizontal stabilizer is 40 feet long.
Most pieces of debris were 3 feet or smaller, he said.
Ten miles off Port Hueneme, a ship steamed back and forth over the debris field, towing a sonar device through the water to create an image of the bottom detailed enough to distinguish parts of the jetliner from rocks and other natural features or manmade junk like lobster pots.
The task - sailors call it ``mowing the lawn'' - had been expected to take two to three days, but Hammerschmidt said it would likely be completed Friday.
After that, remote-operated vehicles like the one that salvaged the plane's ``black box'' flight recorders will be sent down to take video images and eventually help retrieve bodies and wreckage.
``You can't do it overnight,'' said Navy Capt. Terry Labrecque. ``You have to be methodical.''
The NTSB has previously said that radio transmissions and eyewitness reports from other commercial pilots in the area show the plane turned upside down or ``corkscrewed'' into the water following a series of increasingly desperate maneuvers that lasted at least half an hour.
Also Friday, relatives of victims - many of whom worked for or were connected with Alaska Airlines - were preparing for another private memorial, set for Saturday in the Pepperdine University chapel overlooking the ocean in Malibu. On Sunday, the Coast Guard planned to drop flowers from that service over the crash site.
Fifteen members of various bands of American Indians gathered on marshland near Point Mugu Friday for a ceremony in honor of victim Morris Thompson and his family.
A prominent Native American leader in Alaska and former commissioner for the Bureau of Indian Affairs, Thompson, 61, his wife Thelma and daughter Sheryl were killed in the crash.
The Indians burned sage to cleanse their spirits; passed a pipe, which is a symbol of life; took turns leading tribal chants; then turned east, west, south and north, some pointing feathers to the sky, to honor the four directions.
Only four bodies have been recovered. Relatives waited for word on further efforts to bring back remains.
The wreckage lies in an underwater canyon beneath the Barbara Channel, where depths range from 90 feet at the edges to 700 feet.
A remote-operated underwater vehicle called Scorpio 1 explored a small part of the debris field after bringing up the second flight recorder Thursday, and sent up video images of the plane's tail, with the airline's trademark image of a smiling Alaska native.
The stabilizer that is the focus of the investigation was also videotaped, said John Hammerschmidt, a member of the National Transportation Safety Board. Other than the tail, the only large pieces of the plane spotted on early dives were a section of the fuselage with four windows and several pieces up to six feet wide, Hammerschmidt said.