Japan Commuter AT42 near Kagoshima on Oct 12th 2019, upset causes injury to flight attendant

Last Update: August 18, 2021 / 18:07:55 GMT/Zulu time

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Incident Facts

Date of incident
Oct 12, 2019

Classification
Accident

Airline
Japan Air Commuter

Flight number
JC-3763

Departure
Kagoshima, Japan

Destination
Tanegashima, Japan

Aircraft Registration
JA01JC

Aircraft Type
ATR ATR-42

ICAO Type Designator
AT42

A Japan Air Commuter Avions de Transport Regional ATR-42-500, registration JA01JC performing flight JC-3763 from Kagoshima to Tanegashima (Japan), was enroute at 11,000 feet about 55nm south of Kagoshima at about 11:20L (02:20z) when the aircraft experienced an upset causing serious injuries to a flight attendant. The crew returned the aircraft to Kagoshima for a safe landing about 38 minutes after departure.

Japan's TSB reported the flight attendant received a serious injury, the posterior fracture of right ankle, when the aircraft experienced an upset at about 3200 meters of altitude about 65km (35nm) northnorthwest of Tanegashima.

On Aug 18th 2021 the JTSB released their final report concluding the probable causes of the accident were:

The JTSB concludes that the probable cause of this accident was that the Aircraft was suddenly shaken, therefore, the cabin attendant who was walking along the aisle fell off balance and injured.

It is probable that regarding the Aircraft was suddenly shaken was because the Aircraft attitude changed due to the nose-up pitch control by the flight crew members to avoid exceeding the VMO and the nose-up effects resulting from an increase in the Aircraft speed, following the encounter of localized changes in the wind direction and velocity.

The JTSB analysed:

(1) Cabin Attendant’s Injury

It is highly probable that the cabin attendant, who was walking along the aisle toward the aft of the cabin, fell off balance and injured due to the sudden shaking of the Aircraft in relation to major changes in vertical acceleration (Maximum vertical acceleration: +3.3 G) and roll angle that had been recorded in FDR from around 11:18:28 when the seat belt sign remained off.

(2) Flight Crew Members’ Forecast of Weather Conditions

Based on the weather information provided prior to this flight, PIREP, and flight condition in the round flight which the Aircraft made before this flight between Kagoshima Airport and Kikai Airport, it is probable that the flight crew members anticipated that they would be less likely to encounter turbulence that could affect the Flight.

(3) Atmosphere Conditions

According to Figure 6, at the time of the accident, the outside air temperature decreased, and the wind conditions estimated from FDR records changed from a tailwind (about 20 kt) to a headwind (about 20 kt), and to a tailwind (about 30 kt) in a short time (See Figure 6(a)). In addition, when the Aircraft was flying in the vicinity of the accident site on the way back to Kagoshima Airport, the outside air temperature increased, and the wind conditions estimated from FDR records changed from a headwind (about 20 kt) to tailwind (about 10 kt), and to headwind (about 30 kt) (See Figure 6 (b)).

Therefore, it is highly probable that the Aircraft encountered localized changes in the wind direction and wind velocity and the outside air temperature which were difficult to forecast not being shown in weather information like hourly atmosphere analysis chart.

(4) Responses of the Flight Crew Members

It is highly probable that because the fight crew members did not anticipate the shaking during the descent, the descent speed of 240 kt was selected in accordance with its flight plan for the flight.

As shown in Figure 3, because the IAS of the Aircraft was about to exceed 240 kt after starting to descend, it is highly probable that the FO set the engine power to the flight idle. However, due to changes in the wind direction and wind velocity, and the outside air temperature, the IAS of the Aircraft further increased, therefore, it is highly probable that the PIC and the FO pulled the control columns strongly in the nose-up direction almost at the same time in order to avoid exceeding the VMO. At this time, according to the FDR records, the attitude of the Aircraft changed by 8.6° in the nose-up direction for about one second, and the Aircraft exceeded the VMO for about one second. It is highly probable that the change in the Aircraft’s attitude was caused by the nose-up pitch control provided by the flight crew members and the nose-up effects resulting from an increase in the aircraft speed.

The flight crew members stated the Aircraft did not easily take a noseup, however, there were no descriptions about failure related to the flight control system in the maintenance record of the Aircraft, in addition, the Aircraft examination conducted after this accident found no abnormality.

Accordingly, it is somewhat likely that the nose-up was unsuccessful and the flight crew members felt adequate control was needed, not because there was a failure in the flight control system, but because they pulled the control columns at a higher speed, thus the aerodynamics hinge moment became large.

VMO should not be deliberately exceeded, but is required to be set at the speed that should include a safety margin considering the time for the pilot to respond even when the alarm is activated, so the pilot can reduce the speed to the VMO level without excessive flight control force and special flight skills.

Besides, in the AOM of the Company, it is described that aggressive or large elevators input should be avoided because such input may lead to high load (G) and result in structural damage. Furthermore, as a CAUTION, it is also described that the aircraft must be controlled from one control column only and dual input in opposite direction may result in a Pitch Disconnect.

At the time of the accident, as the Aircraft increased speed and was about to exceed the VMO, the FO pulled the control column, but was not able to reduce the speed as intended, and having seen it, the PIC also pulled his control columns immediately. Those operations by the flight crew members could reduce the degree of exceeding the VMO, however, the FDR recorded the vertical acceleration exceeding the limit load factor. In the examination of the Aircraft conducted after the flight, no failure was confirmed with the Aircraft, however it is probable that exceeding the limit load factor could result in structural damage. It is probable that with due consideration of the criteria set out for the VMO, the flight crew members should have reduced the speed by operations without rapid and excessive flight control force. In addition, as dual input may cause a Pitch Disconnect, it is important with regard to safety that the aircraft shall be controlled from one control column only by either one of the flight crew members in accordance with the AOM of the Aircraft. Furthermore, it is probable that the PIC pulled his control column immediately in order to support the FO, however, from the view point of preventing dual input, when a flight crew member who is not the PF operates the control column, it is required to ensure that they carry it out after clearly expressing the intention of “Take Over” by calling “I Have” without fail.

(5) Vertical Acceleration of the Aircraft

As shown in Figure 3, the changes in the Aircraft’s vertical acceleration (about +0.6 G to about +3.3 G) had been recorded in FDR from around 11:18:28.

In addition, when the Aircraft was flying in the vicinity of the accident site on the way back to Kagoshima Airport, the changes in the vertical acceleration (about +0.2 G to about +1.6 G) were recorded, therefore, it is highly probable that the Aircraft had been shaking before its IAS approached the VMO. It is probable that the Aircraft was shaken because it encountered localized changes in the wind direction and wind velocity shown in Figure 6 (a).

Besides, it is probable that the maximum vertical acceleration of +3.3 G recorded in FDR around 11:18:31 was the result that the vertical acceleration was added because the Aircraft attitude changed when the PIC and the FO pulled the control columns strongly in order to avoid exceeding the VMO when the IAS had approached the VMO while the Aircraft had been shaking.

Furthermore, the result of the calculation by the Design and Manufacturer has given +2.7 G as the vertical acceleration caused by the fact which the PIC and the FO aggressively pulled the control columns, and the maximum vertical acceleration of +2.8 G has been obtained from the examination which simulated the Aircraft’s attitude changes using a simulator.

(6) Responses of the Company

The Company had not provided the flight crew members with recommended operation procedures in the case of approaching or exceeding the VMO.

It is probable that the Company needs to provide information and
training regarding the VMO including operating procedures for safe aircraft operation.