|Title:||In-flight upset, Trans World Airlines, Inc., Boeing 727-31, N840TW, near Saginaw, Michigan, April 4, 1979|
|Micro summary:||This Boeing 727-31 experienced a serious in-flight upset, losing some 34,000' of altitude before recovery.|
|Event Time:||1979-04-04 at 2148 EST|
|Publishing Agency:||National Transportation Safety Board (NTSB)|
|Site of event:||Near Saginaw, MI, FL390|
|Departure:||John F. Kennedy International Airport, Jamaica, New York, USA|
|Destination:||Minneapolis/St. Paul International Airport, Minnesota, USA|
|Airplane Type(s):||Boeing 727-31|
|Operator(s):||Trans World Airlines|
|Type of flight:||Revenue|
|Executive Summary:||About 2148 EST, on April 4, 1979, a Trans World Airlines, Inc., Boeing 727, operating as Flight 841, entered an uncontrolled maneuver at 39,000 feet pressure altitude near Saginaw, Michigan. The aircraft descended to about 5,000 feet in about 63 seconds before the flightcrew regained control. About 2231, the flightcrew made an emergency landing at Metropolitan Airport, Detroit, Michigan. Of the 89 persons aboard, 8 passengers received minor injuries. The aircraft was damaged substantially.|
The flight was cruising in visual flight conditions at night at 39,000 feet when the uncontrolled maneuver began; there was no turbulence. There was a cloud layer near 20,000 feet, and at 2155, the reported weather at Saginaw was 500-foot overcast with 3 miles visibility in light snow; small breaks were reported in the overcast.
Analysis of the evidence indicated that the uncontrolled maneuver began about 2147:47 with isolation of the aircraft's No. 7 leading edge slat (on its right wing) in the extended or partially extended position. During the preceding 14 seconds, the aircraft had rolled slowly to the right to about 35° of right bank and was returned to near wings level flight. Thereafter, the aircraft rolled again to about 35° of right bank in about 4 seconds. About 2147:51, the right roll was stopped near 35° of bank for a few seconds. At that time, the aircraft reached a condition wherein mach number, angle of attack, and sideslip combined to reduce the aircraft's lateral control margin to zero or less, and the aircraft continued to roll to the right in a descending spiral. During the following 33 seconds, the aircraft completed 360° of roll while descending to about 21,000 feet. The aircraft entered a second roll to the right during which the No. 7 slat was torn from the aircraft. Control of the aircraft was regained about 2148:58 at an altitude of about 8,000 feet.
The Safety Board determines that the probable cause of this accident was the isolation of the No. 7 leading edge slat in the fully or partially extended position after an extension of the Nos. 2, 3, 6, and 7 leading edge slats and the subsequent retraction of the Nos. 2, 3, and 6 slats, and the captain's untimely flight control inputs to counter the roll resulting from the slat asymmetry. Contributing to the cause was a preexisting misalignment of the No. 7 slat which, when combined with the cruise condition airloads, precluded retraction of that slat. After eliminating all probable individual or combined mechanical failures, or malfunctions which could lead to slat extension, the Safety Board determined that the extension of the slats was the result of the flightcrew's manipulation of the flap/slat controls. Contributing to the captain's untimely use of the flight controls was distraction due probably to his efforts to rectify the source of the control problem.
|Learning Keywords:||Operations - Altitude Excursion|
|Operations - Upset in-flight (extreme attitudes, stall, spin)|
|Consequence - Damage - Airframe or fuselage|
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