NTSB Identification: CHI01IA055.
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Scheduled 14 CFR operation of AMERICAN EAGLE AIRLINES, INC. (D.B.A. AMERICAN EAGLE AIRLINES)
Incident occurred Wednesday, December 27, 2000 in CHICAGO, IL
Probable Cause Approval Date: 08/26/2002
Aircraft: Embraer EMB-135LR, registration: N721HS
Injuries: 12 Uninjured.
NTSB investigators used data provided by various sources and may have traveled in support of this investigation to prepare this aircraft incident report.
The captain said that during takeoff from O'Hare International Airport (ORD) the airplane accelerated normally, rotated, and "jumped into the air". At 800 feet agl, the captain called for the climb checklist. It was about this time that the captain noticed that he could not trim nose down. The captain had the first officer check his trim switch and the backup system. They did not respond. The captain elected to bring the airplane back to ORD. The captain said that both he and the first officer had their control yokes pushed forward to the stop and were still climbing. The captain said he was finally able to stop the climb and level the airplane at approximately 8,000 feet. The captain said they declared an emergency and referred to the Pitch Trim 1 and 2 Failure checklists. The checklist directed they lower flaps to 9 degrees. "When we brought in the flaps, the aircraft pitched way nose high. We were out of control." The captain regained control of the airplane and had the first officer retract the flaps. The captain said they lowered the landing gear. It improved the airplane's stability slightly. They pulled and reset the trim circuit breakers twice. These actions did nothing. The captain said he lined up for an approach to runway 9R. The captain determined he was too high to land, so he executed a 360-degree descending turn. On completion of the turn, the captain said they needed to slow down so they deployed the spoilers. The captain said the airplane abruptly pitched way up. The captain said he and the first officer pushed both yokes forward. The captain advanced the throttles, and retracted the spoilers. "That second, I banked hard left, 50 to 60 degrees as I recall, and chopped the power. It took all our abilities to get the nose down." After they got the airplane back under control, the captain said approach control informed them that runway 4R was straight ahead. The captain elected to land on runway 4R. The captain said he left the airplane configured as it was (landing gear down, flaps and spoilers retracted) and flew a long shallow approach. "I said to myself, God please let me land this airplane. Over the runway, I chopped the power and let it settle on the runway." A post-incident examination of the airplane's spoiler control unit revealed that when the spoilers were given the command to retract, the unit was not sending an input to the horizontal stab control unit (HSCU) to put in 1 unit of nose down stabilizer trim. Examinations of the trim system components and the other airplane systems revealed no anomalies. Following the incident, the airplane's manufacturer revealed that the horizontal stab actuator was determined to be inadequate to move the horizontal stabilizer in all flight conditions. "The incidents are most likely caused when the flight crew fails to trim the airplane after takeoff before reaching a certain airspeed where the air loads on the stabilizer may overpower the trim actuator, resulting in the horizontal stabilizer not responding to the pitch trim command from the flight crew." The manufacturer issued an alert service bulletin mandating the installation of a cockpit placard and revisions to the airplane flight manual establishing a maximum speed of 160 knots to pitch-trim after takeoff. The FAA issued an emergency AD mandating the installation of the cockpit placard and revisions to the airplane flight manual. The FAA has also tasked the manufacturer to make design changes that will enable the trim actuator to handle increased load limits. The FAA has also mandated changes that will provide improved pitch trim failure indications and ergonomic improvements of the yoke trim switches.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The jammed horizontal stabilizer trim that occurred during the airplane's initial climb after takeoff. Factors relating to the incident were the inadequate capability of the horizontal stabilizer trim actuator to move the stabilizer during all flight phases, and the inadequate design of the system by the manufacturer. Full narrative available
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