First Flying DHC6 at Aguni on Aug 28th 2015, runway excursion on landing

Last Update: December 29, 2016 / 16:21:28 GMT/Zulu time

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Incident Facts

Date of incident
Aug 28, 2015

Classification
Accident

Flight number
DAK-101

Destination
Aguni, Japan

Aircraft Registration
JA201D

ICAO Type Designator
DHC6

A First Flying De Havilland DHC-6-400 Twin Otter, registration JA201D performing flight DAK-101 from Okinawa to Aguni (Japan) with 12 passengers and 2 crew, landed on Aguni's runway 19 at about 08:55L (23:55Z Aug 27th) but veered right off the runway, went across a ditch and came to a stop entanged into bushes. All 14 occupants were taken to a local hospital with minor injuries, the aircraft sustained substantial damage.

The weather was reported good at the time of the accident.

Japan's Ministry of Transport reported the right hand main tyre got punctured during landing causing the aircraft to veer right about midway down the runway and impact the perimeter about 23 meters off the edge of the runway. There was a fuel leak but no fire.

The airline reported the captain had 5,500 hours of flying experience, the first officer 16,800 hours of flying experience.

Japan's TSB have dispatched investigators on site.

No METARs and no local weather station reports are available.

On Dec 29th 2016 the JTSB released their final report concluding the probable causes of the accident were:

It is highly probable that this accident occurred because, when the Aircraft landed, the PF could not properly control the aircraft that had started to deflect after touchdown, as a result of which it departed from the side of the runway and collided with the Perimeter Fence, and the aircraft was damaged.

It is probable that the Aircraft started to deflect after touchdown because the PF forgot the checklist and the PIC as PM did not properly monitor or did not perform the necessary pointed out, as a result of which the Aircraft touched down with the nose wheel deflected to the right.

It is somewhat likely that the PF could not properly control the Aircraft that had started to deflect after touchdown because he did not have sufficient knowledge concerning the aircraft system of the Aircraft, as a result of which he could not fully understand the situation when the deflection started. It is somewhat likely that the inadequate response of the PIC in the event of an unforeseen situation contributed to this.

It is probable that PF had insufficient knowledge and could not fully understand the situation when the deflection started, because the Company had not properly confirmed the effectiveness of ground school training that should be held prior to route training and training on the establishment of knowledge.

The JTSB reported one crew member and 10 passengers received minor injuries and the aircraft received substantial damage as result of the occurrence.

The first officer (62, ATPL, 16,323 hours total, 61 hours on type) was pilot flying, the captain (57, ATPL, 5,685 hours total, 196 hours on type) was pilot monitoring. The first officer was in training to become pilot in command on the DHC6 and occupied the left hand seat. The captain had received training as flight instructor, in particular taking control from the trainee, and occupied the right hand seat.

During briefing for landing the first officer stated, he wanted to use flaps 20 resulting in a Vref of 77 KIAS, the captain agreed.

The aircraft positioned for the approach and crossed the runway 19 threshold at 75 KIAS. The aircraft touched down on a heading of 189 degrees magnetic, bank angle 0.5 degrees to the left and 76 knots over ground. Immediately after the wheels touched down a screeching sound could be heard on the CVR, that continued until the aircraft came to a stop. The captain instructed "Don't brake" twice, the aircraft began to veer right off the runway and departed the paved surface at a heading of 201 degrees magnetic at 59 knots over ground. About 3 seconds after the aircraft departed the paved surface the CVR recorded the sounds of a collision.

In his postflight testimony the captain stated, that after touchdown due to the screeching sound and abnormal right hand tendency of the aircraft he believed the first officer had applied asymmetric brakes, at that time he did not have his feet on the brake pedals. As the first officer did not seem to be able to correct the tendency, the captain operated the rudder and covered the power levers with his hands attempting to apply asymmetric reverse power, however the right hand tendency did not stop.

The first officer reported the right hand tendency started immediately when the nose gear touched down and he had the sensation as if something was holding the nose. He applied left rudder, but this did not change the right hand tendency. He had confirmed the nose wheel steering tiller was in its center position before landing. The first officer believed nose wheel and rudder were mechanically linked, so that the nose wheel would also move when the rudder is being operated.

Examination of the nose wheel steering mechanism showed the nose wheel was deflected by 31.5 degrees to the right when the nose wheel steering (NWS) mechanism was removed from the aircraft. The aircraft manufacturer subsequently examined the mechanism, performed tests and reported that the NWS was operational reaching its maximum left and right deflections, inputs on the nose wheel steering tiller would create a proper deflection, the mechanism would return to its center position when the force on the steering tiller was removed. However, the manufacturer added, there was a creep on this NWS. The aircraft manufacturer presented his opinion:

The NWS of the Aircraft was working mostly the same as a serviceable product, except for the phenomenon of a creep.

It is probable that the cause of a creep phenomenon was internal damage to the hydraulic pressure working mechanism, but this could not be identified during this test.

Since the phenomenon of a creep seen after applying force without steering commands input only arose when the nose wheel was not subject to force, and the extent was very limited and not uniform, it is probable that there is no problem in the directional control mechanism after landing.

The JTSB analysed: "the PF had a conversation with the PIC concerning the state of scattered cloud around the Airport at 08:48:00, immediately after finishing the landing briefing at 08:46:37. However, there was no record that the DESCENT & APPROACH CHECKLIST and LANDING CHECKLIST had been performed by the time of touchdown at 08:54:31, while there is also no record of a conversation confirming the NWS position without using the checklists. In view of these facts, it is highly probable that the Aircraft made its approach without the procedure for confirming that the nose wheel is centered and the checklist being performed before landing." and later analysed: "It is highly probable that the Aircraft touched down near the runway centerline with the nose wheel slightly deflected to the right, then rolled with the nose gradually turning to the right, and started deviating to the right when it was near the halfway position on the runway."

The JTSB analysed with respect to the Nose Wheel Steering mechanism:

As described in 2.13.1.1, there is no mechanical connecting mechanism between the NWS of the Aircraft and the rudder flight control system. If an aircraft takes off with the nose wheel centered, the dead weight of the nose wheel will cause the centering latch to engage with a slot on the airframe side and the nose wheel will be locked in a position (center) with the nose wheel centered.

As described in 2.13.1.2 (1), the PTM explained that the nose wheel must be centered after every takeoff by moving the NWS control lever towards the center until the centering latch locks in the center position and resistance is felt, because the centering latch will not engage properly if the nose wheel is not centered at takeoff. But there was no statement of this content in the training manual of the Company.

As described in 2.1.2 (2), the PF stated that the control lever, which should have been in the center position based on marking after takeoff, had previously been known to move from the center in the before landing check.

In view of these facts, it is probable that the PF and the PIC did not have a detailed understanding of the system involving the centering latch that locks the nose wheel after takeoff, and even in the flight training undertaken by them both before route training, had only confirmed the marking of the center position visually, but had not moved the control lever to confirm that resistance is felt. It is probable that this is the reason why situations in which the centering latch did not engage with the slot on the airframe side and the nose wheel was not locked in the center position during flight had occurred in the past.

The JTSB analysed: "it is highly probable that the Aircraft had made its approach without it being confirmed that the NWS was in the center position before landing. It is probable that this was because the PF was distracted by the situation of clouds around the Airport and had thus forgotten to perform the procedures to be done by memory and to give instructions for the checklist to be performed, and also because the PIC, as the PM, did not properly monitor the situation of checklist accomplishment by the PF or did not perform the necessary pointed out."
Incident Facts

Date of incident
Aug 28, 2015

Classification
Accident

Flight number
DAK-101

Destination
Aguni, Japan

Aircraft Registration
JA201D

ICAO Type Designator
DHC6

This article is published under license from Avherald.com. © of text by Avherald.com.
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