Oriental Bridge DH8D at Fukue on Oct 23rd 2020, hard touchdown and tail strike
Last Update: September 30, 2022 / 15:08:26 GMT/Zulu time
The aircraft was unable to continue service, the return flight OC-92 was cancelled (35 passengers were affected).
The airline confirmed the aircraft made a hard landing and suffered a tail strike while landing in Fukue. There were no injuries. The occurrence was rated an accident and reported to Japan's Ministry of Transport. Japan's TSB is going to investigate.
Fukue Airport features a runway 03/21 of 2000 meters/6560 feet length. LOC and VOR approaches are published for both runways 03 and 21.
On Sep 30th 2022 the JTSB released their final report concluding the probable cause of the accident was:
In this accident, the JTSB concludes that the probable cause of this accident was that the Aircraft was most likely in an excessive nose-up attitude and the lower side of its tail contacted the runway because the captain continued the nose-up operation until moments before the touchdown since the Aircraft did not stop descending due to the airspeed reduction caused by turbulence during the landing flare.
The JTSB summarized the sequence of events:
At 08:49 on October 23, 2020, a Bombardier DHC-8-402, registered JA845A and belonging to Oriental Air Bridge Co., Ltd. (hereinafter referred to as "the Company"), took off from Fukuoka Airport for Fukue Airport as its scheduled flight 93. The captain sat in the left seat as PF and the FO sat in the right seat as PM.
When the Aircraft was cruising at an altitude of 10,000 ft, the captain and the FO made preparations for instrument approach landing on Runway 03 at Fukue Airport, and the captain held an approach briefing. As the calculated reference landing speed (hereinafter referred to as “the VREF”) was 119 kt at this time, the captain added 10 kt and set the target approach speed to 129 kt.
The captain told the FO to approach changing from Instrument Flight Rules (IFR) to Visual Flight Rules (VFR) if there was no problem in weather. When the captain and the FO checked the aerodrome routine meteorological reports (METAR) for the Airport reported at 09:00, it was under visual meteorological conditions and the wind direction and velocity were also within the limitations for landing at the Airport, which were stipulated in the Company ’ s route manual. In addition, the wind conditions for the airport confirmed by company radio were within the limitations despite some changes in the wind direction and velocity.
At about 09:10, as the captain and the FO visually recognized Fukuejima Island where the Airport is located, the captain changed the flight rule from IFR to VFR and started to descend. There was air current disturbance at an altitude of 5,000 ft or below while descending, and the Aircraft continued descending while shaking intermittently. At about 09:12 when the Aircraft established communication with Fukue Remote* and was informed of the wind direction and velocity at the Airport, the wind conditions were within the wind direction and velocity limitations established by the Company. Therefore, the captain continued approaching.
At 09:21:13, the Aircraft reported to Fukue Remote that it had reached the Runway 03 right base. At about 09:23, the Aircraft was approaching at an altitude of about 1,200 ft over the Runway 03 final approach course, and at 09:23:42, the captain disengaged the autopilot system and switched to manual control at an altitude of about 700 ft.
As the wind direction was 340° to 350° and the wind velocity was 20 to 30 kt and turbulent air was generated in the area around the final approach course according to on-board observation, the Aircraft was approaching while shaking intermittently. At this time, the Aircraft approach angle went below 3° approach path and its airspeed was also increasing. When the Aircraft was passing the altitude of about 600 and 450 ft, the airspeed increased and exceeded the target approach speed that is a reference speed, and thus the FO made a deviation call to inform the captain of the excessive speed.
Although the Aircraft frequently changed the approach path and its speed during the final approach, the captain continued to approach targeting somewhere in the middle between the aiming point marking and the runway touchdown zone marking in front as its aiming point while performing corrective operation repeatedly, and the Aircraft passed the runway threshold at a speed of 131 kt. At 09:24:29, the airspeed indicator in the right seat momentarily showed that the airspeed decreased to 118 kt at an altitude of about 30 ft AGL and the aiming point also moved close to the runway touchdown zone marking in front. Therefore, the FO made a deviation call. The captain continued to approach the runway and commenced to flare at an altitude of about 20 ft AGL because the airspeed indicator in the left seat showed 124 kt and the touchdown point would usually be extended by flaring. The captain lifted the nose of the Aircraft as usual, but the Aircraft did not stop sinking (the descent rate was not reduced), thus the captain pulled the control column to nose up. When flaring the Aircraft, the captain intended to adjust the attitude of the Aircraft for the touchdown after he stopped sinking by performing a noseup operation, however, the descend rate was not reduced as the captain had expected, and the Aircraft touched down at 09:24:32.
After the Aircraft touched down, the warning light in the cockpit came on and a message indicating that the fuselage had touched the runway was displayed. When the captain performed visual inspections after landing, traces of contact with the runway surface were confirmed on the outer skin of the lower aft fuselage. After that, a detailed examination of the damage to the Aircraft performed by a mechanic confirmed not only damage to the outer skin but also damage and deformity on the structural members inside the Aircraft.
The JTSB analysed:
As the Aircraft was shaking at an altitude of 5,000 ft or below during the descent, turbulence was most likely generated at the bottom layer of the airspace around the airport.
In addition, judging from the wind direction and velocity values observed at the Airport at around the time of the accident, the north-northwest winds with gusts of wind were likely prevailing, around the final approach course, turbulence was possibly generated amid the influence of geographical features on the windward side.
The data of pressure altitude and airspeed after passing the runway threshold were taken every one second and recorded in the FDR of the Aircraft, in which the difference between the right and left and the variation width fluctuated widely. However, while the pressure altitude fluctuated widely, the radio altitude uniformly varied at a rate of 10 ft/sec. So, certainly, the Aircraft was descending with the descent rate of 600 ft/min after passing the runway threshold. As a result, the values of the pressure altitude of the Aircraft most likely fluctuated due to a disturbance surrounding the Aircraft, and turbulence was generated over the runway of the Airport. Besides, as the airspeed was largely reduced compared to the ground speed change calculated with the track information on the GPS and others, after the Aircraft passed the runway threshold, fluctuating wind direction and velocity due to turbulence most likely resulted in a rapid decrease in the headwind component to the Aircraft.
During the Aircraft’s final approach, it was most likely that large pitch attitude and airspeed fluctuations occurred due to the rough air.Therefore, it was more likely that the captain made an approach while performing a corrective operation frequently on the final approach to maintain the target approach speed and approach path.
During the final approach, the target approach speed of the Aircraft changed and exceeded the airspeed as registered in the Company’s Airplane Operating manual for the Aircraft, which resulted in the FO’s deviation call.
This is probably because the airspeed of the Aircraft momentarily changed due to the wind direction and velocity fluctuations (gusts of wind) as a result of turbulence.
Furthermore, during the final approach of the Aircraft, without making the speed, pitch attitude and power setting settled and stable, the captain continued to approach up to the runway threshold while performing a corrective operation. The Company's Airplane Operating Manual stipulates that a goaround should be performed when the non-stabilized state continues at an altitude of 1,000 ft or below over the runway, however, in the AOR, it is permitted to continue to approach when such conditions are temporarily and remain within a corrective range, and the corrective operations are proactively performed. Therefore, the captain probably continued to approach while performing corrective operations.
Condition of the Aircraft after passing the runway threshold
According to the FDR records (Figure 1), the engine torque dropped from about 19 to 12 % after the Aircraft passed the runway threshold. And the airspeed in the left seat (captain’s side) was 131 kt (VREF+12 kt) when it passed the runway threshold but decreased to 116 kt (VREF － 3 kt) at the time of touchdown. As the airspeed of the Aircraft dropped 15 kt in speed in the left seat and 11 kt in the right seat for four seconds from when the Aircraft reached the runway threshold to when it touched down, the airspeed decreased most likely at the deceleration rate of about 3 kt/sec from when the Aircraft passed the runway threshold to when it touched down. This airspeed reduction was most likely caused by the decrease in headwind component because the change in ground speed was small.However, the deceleration rate of about 3 kt/sec was too large for the speed change after passing the runway threshold, therefore, it is highly probable that the Aircraft was flaring while greatly decreasing the airspeed.
Most likely the lift of the Aircraft decreased as the airspeed decreased, and therefore, probably the control column input during flare operations was not enough to stop descent. For this reason, it is probable that as the captain continued to pull the control column to stop the descent, the Aircraft was in an excessive nose-up attitude with the pitch angle reaching a maximum value of 9° immediately before touchdown, the Aircraft touched down before stopping descent, and the lower side of its tail contacted the runway.
In addition, because the Aircraft was flaring while greatly decreasing its airspeed after the Aircraft passed the runway threshold, it probably became difficult for the captain and the FO to predict the Aircraft behavior and they failed to make a proper judgement on power adjustment or go-around within a little time to touchdown.
The Company's AOR stipulates that even if the parameter values related to the stabilized approach exceed the estimated criteria of the significant deviation due to a sudden change of wind direction or disturbance in air stream, the values exceeding the criteria are allowed if it is temporary, could be adjusted, and is being adjusted proactively. However, in this case, it is important to make the aircraft parameters settled and stable by performing corrective operations. Besides, even after passed the runway threshold, it is desirable to perform a go-around proactively when the aircraft behavior becomes different from pilots’ prediction due to disturbance in air stream or others, because it is difficult to take the appropriate responses within a little time to touchdown.
RJFE 230300Z 33015KT 300V360 9999 SCT035 16/08 Q1013
RJFE 230200Z 34015KT 300V010 9999 FEW030 SCT035 16/08 Q1013
RJFE 230100Z 33021G33KT 9999 FEW030 SCT035 16/08 Q1013
RJFE 230000Z 34018G31KT 310V010 9999 FEW030 SCT035 15/07 Q1013
RJFE 222300Z 34018KT 9999 FEW035 SCT040 15/07 Q1012
RJFE 221000Z 35008KT 9999 -SHRA FEW010 SCT030 BKN035 17/16 Q1011
This article is published under license from Avherald.com. © of text by Avherald.com.
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