Accident Overview

Photo of China Airlines A300 takeoff
Photo of China Airlines A300 takeoff
Photo copyright Gordon Tan - used with permission

History of Flight

China Airlines Flight 140 departed from Taipei International Airport, Taiwan on April 26, 1994 towards its destination of Nagoya Airport, Japan (flight plan route). After initial descent and contact with Nagoya Approach Control, the flight was cleared for the Instrument Landing System (ILS) approach to runway 34 (ILS 34 approach) and was switched to the Nagoya tower frequency at approximately 2007 local time. It was nighttime and Nagoya airport weather at the time was reported as winds from 280 degrees at 8 knots, visibility of 20 kilometers, cumulus clouds at 3,000 feet and a temperature of 20 degrees Celsius. During the initial phase of the approach, both autopilot systems (AP1 and AP2) were engaged as well as the auto throttles. After passing the ILS outer marker and receiving landing clearance, the first officer, who was the pilot flying, disengaged the autopilot system and continued the ILS approach manually.

Photo of A300 Cockpit
Photo of A300 Cockpit
Photo copyright John Padgett - used with permission
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When passing through approximately 1,000 feet on the approach glidepath, the first officer inadvertently triggered the GO levers placing the auto throttles into go-around mode, which led to an increase in thrust. This increase in thrust caused the aircraft to level off at approximately 1,040 feet for 15 seconds and resulted in the flight path becoming high relative to the ILS glideslope. The captain recognized that the GO lever had been triggered and instructed the first officer to disengage it and correct the flight path down to the desired glide slope. While manually trying to correct the glide path with forward yoke, the first officer engaged the autopilot, causing it to be engaged in the go-around mode as well. As he manually attempted to recapture the glide slope from above by reducing thrust and pushing the yoke forward, he was providing pitch inputs to the elevator that were opposite the autopilot commands to the THS, which was attempting to command pitch up for a go around.

The THS progressively moved from -5.3 degrees to its maximum nose-up limit of approximately -12.3 degress as the aircraft passed through approximately 880 feet. During this period the first officer continued to apply increasing manual nose-down command through forward yoke control which resulted in increasing nose-down elevator movement, opposite the THS movement, masking the out-of-trim condition. The first officer attempted to use the pitch trim control switch to reduce the control force required on the yoke. However, because pitch trim control of the THS is inhibited during autopilot operation, it had no effect. In a normal, trimmed condition the THS and elevator should remain closely aligned. However, because of the opposing autopilot (nose up) commanded THS and manually commanded elevator (nose down) for approximately 30 seconds, the THS and elevator became "mis-trimmed". 

Photos of China Airlines Flight 140 crash scene
Photos of China Airlines Flight 140 crash scene
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Passing through approximately 700 feet, the autopilot was disengaged but the THS remained at its last commanded position of -12.3 degrees. Also at this time, due to the thrust reduction commanded by the first officer, the airspeed decreased to a low level, resulting in an increasing angle of attack (also termed alpha, or AOA). As a result, the automatic alpha floor function of the aircraft was activated, causing an increase in thrust and a further pitch-up. The alpha floor function of the A300 is an AOA protection feature intended to prevent excessive angles of attack during normal operations. Because of the greater size of the THS relative to the elevator (approximately three times greater in terms of surface area), the available elevator control power or authority was overcome as the aircraft neared 570 feet on the approach. Upon hearing the first officer report that he could not push the nose further down and that the throttles had latched (alpha floor function engaged), the captain took over the controls unaware of the THS position.

Photo of China Airlines Flight 140 crash scene
Photo of China Airlines Flight 140 crash scene

Upon assuming control, the captain initially attempted to continue the approach but was surprised by the strong resistive force to his full nose-down control inputs. He retarded the throttles in an attempt to recapture glide slope. Unable to control the increasing nose-up pitch, which had reached 22 degrees, he called for the GO-lever shortly thereafter in attempt to execute a go around. The increasing thrust added additional nose-up pitch moment and resulted in and uncontrolled steep climb as airspeed continued to decrease and AOA continued to rise. During the attempted go-around, the captain only operated the pitch trim briefly, indicating he was unaware of the mis-trimmed position (extreme nose-up) of the THS. Furthermore, flaps/slats had been retracted two positions (30/40 to 15/15) to the go-around setting, which increased the airplane pitch up and reduced the stall margin. The aircraft continued to climb steeply up to 1,730 feet with AOA rapidly increasing and airspeed decreasing, reaching a maximum pitch angle of approximately 53 degrees until the stall warning and subsequent stall.

Once stalled the aircraft nose lowered to a steep dive and the captain applied full aft yoke in an attempt to recover from the dive; however, the aircraft remained stalled until impact.

An animation of the accident flight path and factors which contributed to the accident are available at the following link: (Accident animation).

A300 Pitch Control

Photo of A300 Tail showing Stabilizer and elevator
Photo of A300 Tail showing Stabilizer and elevator
Photo copyright Wim Callaert - used with permission
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Critical to this accident are the pitch control surfaces, consisting of the Trimmable Horizontal Stabilizer (THS) and elevator. The greater size of the THS provides much greater control power than that available from the elevator. 

Figure of Control Wing Surfaces of A300
Figure of Control Wing Surfaces of A300

A300 Auto Flight System

Illustration of A300 Cockpit
Illustration of A300 Cockpit
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The A300 Auto Flight System (AFS) is designed to assist in control of the aircraft in all phases of flight from takeoff through landing. The control surfaces are controlled by a servo system receiving command signals from the Flight Augmentation Computer (FAC), the Flight Controls Computer (FCC), and the Thrust Control Computer (TCC). Key functions provided by each as they relate to this accident are as follows:

Flight Augmentation Computer (FAC) provides yaw damping functions to support rudder control for dutch roll damping, turn coordination, and autopilot assistance in case of engine failure to counter lateral acceleration/yaw during recovery. The FAC also provides pitch trim commands to the THS. Specific pitch trim command functions important to this accident include:

  • Electric Trim: Pitch control loads may be alleviated using the electric trim switches on each control yoke, which adjusts the position of the THS. Electric trim is available in manual flight or when the autopilot is in the Command Wheel Steering (CWS) mode.
  • Illustration of FMA Displays
    Illustration of FMA Displays
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  • Auto Trim: Auto trim is a function activated by the autopilot which commands the THS based on the command mode of the autopilot.
  • Override Function: The pitch trim modes can all be overridden by manual movement of the pitch trim wheel located in the center console of the flight deck. Movement of this wheel is designed to disconnect the pitch trim system and allow pilots to override the THS.
  • Flight Envelope Protection /Alpha Floor Protection: This function is intended to protect the aircraft from stall by automatically providing maximum thrust when excessive AOA is detected. When alpha floor is engaged, "THR L" (throttles latched) is indicated on the Flight Mode Annunciator (FMA) on the pilots' primary flight display and the throttle levers move forward towards maximum thrust at a rate of eight degrees per second.

The Thrust Control Computer (TCC) and Auto Throttle System (ATS) provide thrust commands to the engines based on throttle position and/or signals to maintain the thrust limit or a target thrust. The flight crew can override the auto thrust system and control the engines manually by light control pressure on the throttle levers.

Photo of GO Lever Location
Photo of GO Lever Location
Photo copyright Tzewei Pang - used with permission
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The Flight Control Computer (FCC) provides the functions of the autopilot/flight director (AP/FD) in a variety of modes (basic, altitude, level change, profile, heading select, navigation, VOR, LOC, takeoff, land, and go-around modes). AP/FD mode is selected by the crew through push buttons located on the Flight Control Unit (FCU) just below the glare shield. Of the several AP/FD modes available, the following are important to this accident:

  • Land mode: Land mode is designed to capture ILS glide slope, guiding the aircraft to the runway axis and to flare. Land mode is engaged through the land pushbutton on the FCU with the following conditions met: 
  1. Radio altimeter height greater than 400 feet above ground level
  2. ILS frequency and runway course selected on ILS control panel

Land mode is disengaged by any of the following: 

  1. Selection of go-around mode
  2. Pressing the land mode button again
  3. Selecting another AP/FD mode on the FCU
  • Go-around mode: Go-around mode was designed to provide both lateral and longitudinal guidance during the execution of a go-around maneuver. ATS is automatically engaged and longitudinal guidance is provided to maintain the reference speed. This mode is also designed to maintain wings level. Go-around mode is activated by triggering the GO levers on the throttles so long as slats/flaps are extended to at least 15 degrees. Go-around mode may be disengaged by selecting another AP/FD mode except for land mode.
Photo of Left Side Thrust Lever
Photo of Left Side Thrust Lever

Autopilot Override Function: At the time of this accident, the design of the A300 auto-flight system would disconnect the autopilot if the pilot applied manual pitch inputs to the control wheel greater than 15 kilograms (33 pounds) in all modes except land and go around. In land and go-around modes the system was designed to allow the pilot to override autopilot elevator control. However, this action would not disconnect the autopilot control of the THS regardless of the control force applied. The Flight Crew Operating Manual (FCOM) explained, "This override was conceived in order to protect the pilot against AP abnormal behavior." The FCOM also included the following caution:

"On the longitudinal axis, the autopilot override does not cancel the AP auto-trim orders. So with the AP in CMD, if the pilot counteracts the AP (elevators order) the AP will move the THS (auto-trim order) so as to maintain the A/C on the scheduled flight path. A risk of out of trim is real - and may lead to a hazardous situation in land and go-around mode only."

THS-in-motion Flight Crew Awareness/Warning

Photo of accident airplane
Photo of accident airplane

The design of the A300 provides the following to inform/warn the crew of movement of the THS:

  1. Visual trim indicators located on the center pedestal which display current position of the THS.
  2. Manual pitch trim control wheels (one on each side of the pedestal) which contain both position markings and turn according to THS movement.
  3. THS motion warning which provides an aural warning during periods of use of the electric pitch trim switches located on each control yoke.

As cited in the accident report, both the visual indicators and manual pitch trim wheels are outside the pilot's field-of-view while looking forward along the aircraft's flight path and may be difficult to accurately read in a darkened flight deck as was the case for this nighttime approach. Additionally, by design, the THS aural warning was inhibited during the approach because the autopilot was engaged in a command mode. The accident board concluded that there was inadequate warning or recognition capability for the flight crew to be alerted to the movement of the THS to an abnormal, out-of-trim condition as the flight crew attempted to maintain the approach glide path.

Pitch Effects Due to Thrust

For aircraft with engines below the wing, as is the case with the under-wing mounted engines of the A300, a rapid increase in thrust creates a significant increasing pitch. While the crew was struggling to manually reduce pitch during the approach, the activation of the alpha-floor function, resulting thrust increase, and positive pitch moment further compromised the flight crew's ability to control pitch. As the captain took over control and attempted a go around, the further increase in thrust by the ATS, coupled with the out-of-trim THS, quickly overcame the manual control authority on the elevator and allowed for a severe increase in pitch attitude and accompanying rapid increase in AOA towards stall.

Illustration of Pitch Effects
Illustration of Pitch Effects

Crew Resource Management

The investigation concluded that effective crew resource management was not practiced by the crew. Areas identified by the investigation involved task sharing, standardization of terms used for instruction, response, confirmation and execution of operations, in order to assure that crews maintain appropriate situational awareness. Further identified by the investigation was the manner in which the captain assumed control of the airplane, and a lack of preflight discussion and agreement as to the situations where it might be appropriate for the captain to assume control.

This and several other accidents involving human errors in using aircraft automation sparked increased focus on consideration of human factors and automation in the design of transport aircraft.

FAA Human Factors Team Report

In 1994 the FAA launched a study to evaluate all flight crew/flight deck automation interfaces of current generation transport category airplanes. The FAA chartered a human factors team to conduct the study. Team members included experts from the FAA, the European Joint Airworthiness Authorities (JAA), and academia. The objective of the study was to examine the contributing factors from the perspective of design; flight crew training and qualifications; operations; and regulatory processes. The FAA also tasked the team to develop recommendations to address any problems identified.

With regard to autopilot issues, the team identified several specific problematic issues, including:

  • Pilot/autopilot interactions that create hazardous out-of-trim conditions
  • Autopilots that can produce hazardous speed conditions and may attempt maneuvers that would not normally be expected by a pilot; and
  • Insufficient wording in the Airplane Flight Manual regarding the capabilities and limitations of the autopilot.

The full text of this team's report issued in 1996 is available at the following link: (FAA Report: Flightcrew Interfaces and Modern Flightdeck Systems).

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