27 Years ago today: On 26 April 1994 a China Airlines Airbus A300 crashed on approach to Nagoya; killing 264 out of 271 occupants.
|Tuesday 26 April 1994
|1990-10-30 (3 years 6 months)
|Total airframe hrs:
|2 Pratt & Whitney PW4158
|Fatalities: 15 / Occupants: 15
|Fatalities: 249 / Occupants: 256
|Fatalities: 264 / Occupants: 271
|Written off (damaged beyond repair)
|Nagoya-Komaki International Airport (NGO) ( Japan)
|International Scheduled Passenger
|Taipei-Chiang Kai Shek International Airport (TPE/RCTP), Taiwan
|Nagoya-Komaki International Airport (NGO/RJNN), Japan
China Airlines Flight 140 departed from Taipei International Airport, Taiwan, bound for Nagoya Airport, Japan. 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.
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”.
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.
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 impacting the ground tail-first, 300 feet to the right of the runway and burst into flames.
CAUSES: While the aircraft was making an ILS approach to runway 34 of Nagoya Airport, under manual control by the F/O, the F/O inadvertently activated the GO lever, which changed the FD (Flight Director) to GO AROUND mode and caused a thrust increase. This made the aircraft deviate above its normal glide path. The APs were subsequently engaged, with GO AROUND mode still engaged. Under these conditions the F/O continued pushing the control wheel in accordance with the CAP’s instructions. As a result of this, the THS (Horizontal Stabilizer) moved to its full nose-up position and caused an abnormal out-of-trim situation. The crew continued approach, unaware of the abnormal situation. The AOA increased the Alpha Floor function was activated and the pitch angle increased.
It is considered that, at this time, the CAP (who had now taken the controls), judged that landing would be difficult and opted for go-around. The aircraft began to climb steeply with a high pitch angle attitude. The CAP and the F/O did not carry out an effective recovery operation, and the aircraft stalled and crashed.
The AAIC determined that the following factors, as a chain or a combination thereof, caused the accident:
* The F/O inadvertently triggered the Go lever. It is considered that the design of the GO lever contributed to it: normal operation of the thrust lever allows the possibility of an inadvertent triggering of the GO lever.
* The crew engaged the APs while GO AROUND mode was still engaged, and continued approach.
* The F/O continued pushing the control wheel in accordance with the CAP’s instructions, despite its strong resistive force, in order to continue the approach.
* The movement of the THS conflicted with that of the elevators, causing an abnormal out-of-trim situation.
* There was no warning and recognition function to alert the crew directly and actively to the onset of the abnormal out-of-trim condition.
* The CAP and F/O did not sufficiently understand the FD mode change and the AP override function.
It is considered that unclear descriptions of the AFS (Automatic Flight System) in the FCOM (Flight Crew Operating Manual) prepared by the aircraft manufacturer contributed to this.
* The CAP’s judgment of the flight situation while continuing approach was inadequate, control take-over was delayed, and appropriate actions were not taken.
* The Alpha-Floor function was activated; this was incompatible with the abnormal out-of-trim situation, and generated a large pitch-up moment. This narrowed the range of selection for recovery operations and reduced the time allowance for such operations.
* The CAP’s and F/O’s awareness of the flight conditions, after the PlC took over the controls and during their recovery operation, was inadequate respectively.
* Crew coordination between the CAP and the F/O was inadequate.
* The modification prescribed in Service Bulletin SB A300-22-602 1 had not been incorporated into the aircraft.
* The aircraft manufacturer did not categorise the SB A300-22-6021 as “Mandatory”, which would have given it the highest priority. The airworthiness authority of the nation of design and manufacture did not issue promptly an airworthiness directive pertaining to implementation of the above SB.