LAX01LA136
LAX01LA136

On April 19, 2001, at 0948 hours Pacific daylight time (PDT), an Airbus Industrie A320-232, N654AW, encountered turbulence while in cruise flight at 31,000 feet msl near Raton, New Mexico. The flight, which departed New York, New York, at 0858 eastern daylight time, was destined for Las Vegas, Nevada, and landed there at 1113 PDT. One flight attendant was seriously injured; one other flight attendant and 3 passengers received minor injuries; and the airline transport certificated pilot, the second pilot, and the remaining flight attendant and 118 passengers were not injured. The airplane was not damaged. The flight was operated by America West Airlines, Inc., under 14 CFR Part 121, as flight 7, a regularly scheduled domestic passenger flight. The flight was operating on a instrument flight plan and visual meteorological conditions prevailed.

The company flight dispatcher reported that he advised the flight crew of a recently issued significant meteorological notice (SIGMET) via company communications radio about 30 minutes before the accident. The SIGMET was for forecast and reported occasional severe turbulence over southern Colorado and northern New Mexico between 31,000 feet and 39,000 feet. The dispatcher recommended that the flight descend below the area of forecast turbulence or alter course around it. The crew advised they would "discuss the situation and get back with me;" however, the next communication from the flight was about 30 minutes later when they reported the encounter with moderate to severe turbulence over the Cimarron (New Mexico) navigational aide at 31,000 feet and the injury to one flight attendant.

In their report to the Safety Board, the company Director, Operations Safety, reported "At approximately 0915 PDT, the dispatcher communicated to the captain that the flight was approaching an area of forecast moderate to severe turbulence associated with mountain wave activity. The forecast (SIGMET Papa1) covered an area of the front range of the Rocky Mountains, between flight Level 310 (FL310) and FL390. The dispatcher recommended that the flight alter course (to return to the original flight plan in lieu of the direct routing the flight was on) and descend to FL280. The captain queried air traffic control, and upon receiving reports of smooth air at FL310, he descended from FL350 to FL310 and remained on the direct routing. Approaching the area of forecast turbulence, he illuminated the seat belt sign and advised the passengers of the potential for turbulence. He also advised the flight attendants to stow the galley equipment. Approximately 3 to 4 minutes later, the flight encountered Severe Clear Air Turbulence. Once it was determined that there were injured crewmembers and passengers aboard (and that they were receiving medical attention), the captain coordinated with dispatch and the flight landed in Las Vegas with[out] further incident."

The pilot reported he recalled dispatch issued the SIGMET for severe turbulence from 33,000 feet to 37,000 feet and they were cruising at 31,000 feet. There also had been a pilot report of severe turbulence in "that" area. Pilots of other aircraft were telling air traffic controllers that they were experiencing mountain wave activity at higher altitudes (than they were at). The pilot notified the flight attendants, turned on the "fasten seat belt" sign, and made a cabin announcement telling the passengers to remain in their seats as a precautionary measure. "Approximately three to four minutes later, we went from smooth air to a light mountain wave indication followed by an abrupt encounter with severe turbulence which lasted about seven to eight seconds. This encounter caused us to drop 400 feet of altitude immediately, the autopilot disconnected and the aircraft attitude was upset to a pitch down followed by a momentary TCAS [Traffic Collision Avoidance System] warning. Items loose in the cockpit became airborne. It was the first officer's leg so he continued to fly the aircraft back to our clearance altitude of FL310. We notified ATC [Air Traffic Control] and requested FL280 to find smoother air."

The airplane's digital flight data recorder was read out by the manufacturer, Honeywell Commercial Electronics Systems. The altitude parameter showed the airplane cruised at flight level 350 (FL350, approximately 35,000 feet, msl) until 0909:30, at which time it descended to flight level 310 (FL310, approximately 31,000 feet, msl), arriving there at 0911:30. The airplane remained at FL310 until the turbulence encounter at 0948. Prior to 0948:37, the normal acceleration parameter remained near 1.0. In the 16-second period between 0948:37 and 0948:53 the normal acceleration parameter first increased to 1.441, then dropped abruptly to -0.379, then increased to 1.449, then dropped to 0.105, then increased to 1.348, then dropped abruptly to 0.215 followed by an abrupt increase to 1.371, before returning to approximately 1.0. At 0950:23, the altitude parameter showed the airplane started a descent from FL310 until it leveled at flight level 280 (approximately 28,000 feet, msl) at 0951:55.

A transcript of communications between flight 7 and the Denver Air Route Traffic Control Center was provided by the Federal Aviation Administration (FAA) Northwest Region Quality Assurance Office. At 0930, following a handoff from a different sector, flight 7 checked in and said "[flight] seven at three one zero request a ride report." The controller replied: "expect occasional light chop nothing real bad." At 0935, there were a series of communications, on the same frequency, between United Airlines flight 8146 (at flight level 280) and the controller regarding ride quality. The controller told the United flight that flight level 280 was the "best ride," and that "everything upstairs flight level three five through flight level four one zero is a lot worse it's severe mountain wave and intermittent moderate." The controller then added (to United): "flight level three one zero is occasional light to moderate as well a little worse than flight level two eight zero." At 0946, flight 7 transmitted: "we're just getting a little bit of a nibble here at three one zero but um i'm out looking ahead it looks like two eight zero might be little bit smoother altitude how's it look to you." The controller queried another aircraft at flight level 280, which reported "light ripples," and then told flight 7 that it would be about 3 minutes before he could clear flight 7 to descend to the lower flight level. At 0949:01, flight 7 transmitted: "we just got um a jolt of moderate ah turbulence and we request two eight zero." The controller replied: "traffic twelve oclock and four miles eastbound flight level two niner zero lower when clear." At 0950:02, the controller cleared flight 7 to descend to flight level 280.

The injured flight attendant was one of two in the aft galley when the turbulence was encountered. The other flight attendant, who received minor injuries, reported she had just returned to the aft galley after picking up cabin service items. During her return to the galley, the captain made the announcement about anticipated turbulence. As she reached the aft galley they encountered turbulence. She grasped an assist handle, the other flight attendant grasped one on the opposite side, and they locked forearms in the center. They were "jolted" a couple of times during which she recalled her feet came off the floor and then the turbulence subsided. They "scrambled" toward their jumpseats; however, they encountered additional, more severe, turbulence and it became impossible to hold onto anything. She recalled being thrown about the galley; hitting the ceiling, counters, and doors before being "slammed" to the floor. She landed face down on the floor and thought she had injured her back and both ankles. They were still in turbulence so she crawled on her stomach to the last row of seats and held on to the seat frame. She reported the sounds were deafening and people were screaming. Some overhead bins opened and items fell out. The turbulence subsided and she assisted the injured flight attendant to a seat before helping the remaining flight attendant (in the forward cabin) with passenger and flight duties.

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