NTSB chief details last seconds of Flight 261

Excerpts of today's statement by Jim Hall, chairman of the National Transportation Safety Board, on the investigation of the crash of Alaska Airlines Flight 261:

You will remember that when we released CVR (cockpit-voice recorder) information last week, we told you that when the approximate 31-minute recording began, the pilots were discussing an existing problem with the aircraft's stabilizer trim. According to the FDR (flight-data recorder), the crew had flown for one hour and 53 minutes with the autopilot disengaged. It was at this point that the first event of note occurred.

. . . Approximately 12 minutes before the end of the FDR recording, the data indicate the aircraft was cruising in straight and level flight at an altitude of 31,000 feet and airspeed of 301 knots calibrated air speed (346 mph), with the autopilot engaged. . . . As recorded on the CVR, the crew commented that they were not able to maintain vertical control and actions to overcome the problem were discussed.

The airplane began to descend at an average descent rate of 7,000 feet per minute, more than three times the typical rate of descent from cruise flight. During this sequence the speed brakes were deployed. After about a minute, the aircraft regained what could be characterized as controlled flight. At this point, Flight 261 was at about 24,300 feet.

For the next nine minutes or so, the aircraft was in controlled flight, descending from 24,000 to about 18,000 feet. Toward the end of this period, the crew extended the slats and then extended the flaps for a period of little more than 30 seconds, and the CVR reflects comments that the aircraft is controllable in this configuration. The crew then retracted the slats and flaps. CVR and FDR data show that the airplane remained in control at this time.

Things then began to happen very quickly. The aircraft was at about 18,000 feet, air speed 270 knots (310 mph), pitch attitude 2.7 degrees nose up. The stabilizer was in the full nose-down trim position, and the elevator was deflected more than 12 degrees in the nose-up position. This elevator deflection was approximately 50 percent of full travel.

At this time, the flaps began to extend to 11 degrees. Approximately three seconds after the start of the flap movement, the slats began to deploy.

Beginning at about four seconds after the beginning of the flap/slat deployment, the pitch-attitude data show the airplane pitching nose-down, . . . reaching a nose-down pitch attitude of 59 degrees in approximately 3 seconds. . . . Over the next 2.5 seconds the maximum nose-down attitude of 70 degrees was reached. During this rapid nose-down pitching motion, the aircraft experienced a negative 3-G (G-force) vertical acceleration. . . . The aircraft did not reach level flight thereafter. A 60-degree per second roll rate to the left began, . . . consistent with the airplane rolling into an inverted position. This final descent from 17,900 feet lasted just over a minute. The aircraft wreckage is located at Latitude 34 03.5 North, Longitude 119 20.8 West. . . .

(Hall introduces information from radar.)

You see where we have marked the area of the loud noise we reported to you last week that was heard on the CVR. This basically corresponds to the beginning of the final descent of the aircraft that I've just explained. These primary radar hits might be indicative - and I emphasize MIGHT be indicative - of something coming off Flight 261 near this point.

. . . Using these radar data, we have instructed assets of the U.S. Navy to search an area of the ocean where we believe something that would have departed the aircraft at that point could have landed, about four miles from the main wreckage site. This is of course a difficult task, complicated by the fact that we do not know whether something did actually separate from the aircraft.

As to other activities in this investigation, the Navy has completed mapping the accident area with underwater side scanning sonar and video. This information will help guide us in developing a salvage plan. Last night, the Navy found and recovered about an 8-foot section of what we believe to be the left horizontal stabilizer and some portion of the center horizontal stabilizer.

. . . Our Maintenance Records Group convened in Seattle on Feb. 2 and has interviewed 15 Alaska Airlines maintenance and dispatch personnel in Seattle and Los Angeles. The last heavy maintenance check was a C check on Jan. 13, 1999. C checks are conducted about every 15 months.

This aircraft had two previous stabilizer-trim maintenance write-ups, both of them in 1999. In October, the trim system checked out OK and the aircraft was returned to service. In November, the alternate trim switch was replaced.

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NTSB Web site

Full text of today's briefing and other information on the Flight 261 investigation can be found at www.ntsb.gov. There is also a link from www.seattletimes.com