Thai B772 at Dhaka on Jul 24th 2018, temporary runway excursion

Last Update: May 2, 2019 / 15:00:41 GMT/Zulu time

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Photo of Thai Airways HS-TJD, Boeing 777-200 — Thai Airways HS-TJD, Boeing 777-200 (Photo credit: Alec BHX/KKC / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jul 24, 2018

Classification
Incident

Airline
Thai Airways

Flight number
TG-321

Departure
Bangkok, Thailand

Destination
Dhaka, Bangladesh

Aircraft Registration
HS-TJD

Aircraft Type
Boeing 777-200

ICAO Type Designator
B772

A Thai Airways Boeing 777-200, registration HS-TJD performing flight TG-321 from Bangkok (Thailand) to Dhaka (Bangladesh) with 154 passengers and 16 crew, landed on Dhaka's runway 14 in heavy rains at 12:18L (06:18Z) but burst its right hand main tyres and temporarily veered off the runway to the right. The aircraft returned onto the runway and became disabled while attempting to vacate the runway via the high speed turn off (second last exit runway 14, short taxiway H).

The airline reported the aircraft landed in heavy rains, the right hand tyres burst, the pilots however were able to safely control the aircraft.

Ground observers reported the aircraft veered to the right after touchdown obviously contacting a number of runway edge lights and returned onto the runway.

On May 2nd 2019 The Aviation Herald got hold of the final report by Aircraft Accident Investigtion Group of Bangladesh (AAIGBD) concluding the probable causes of the serious incident were:

The cause of the serious incident was due to ‘Human Factor’, wherein,

a) The flight crew‟s inadequate coordination during manual handling of the aircraft while approach to land resulted the aircraft neither touch down within the „touchdown zone‟ nor at or close to the centerline of the RWY due to inappropriate alignment with the RWY; and,

b) According to the DFDR read out, the PIC applied the left rudder immediately after touch down to bring the aircraft back to centerline. The PIC provided left rudder input for a duration of approximately 19.6s, reaching a peak recorded value of 25.7679 inches (left rudder pedal forward). However, either, the left rudder pedal input was insufficient or, there were requirement to use left wheel brakes also (which was not applied initially) to prevent the aircraft from veering off the right edge of the runway due to inertia.

CONTRIBUTING FACTORS

a) Human factor:

1. Flight crew decision not to hold around the vicinity of the airfield for the weather to clear off and thereafter commence the second approach for landing; and,

2. Flight crew decision, not to go around the second time;

b) Weather factor:

1. Reduced visibility due to rain and thundershower during the approach time; and,

2. Slant visibility restricted pilot vision to sight the RWY late;

c) Maintenance factor:

The right main landing gear tires being Retread may not have sustained the shocks resulting major damages after hitting, one after another, the nine manholes/handholds.

d) Aerodrome Factor:

1. It was observed that there was increased risk of damage to the aircraft from striking a hard vertical surface (the isolation transformer concrete pits for runway lighting system) being close to the runway shoulder.

2. Many (in excess of nine) manholes/handholds, located too close to the RWY edge, having the dimension of about 5 feet (length) x 4 feet (width) x 2 feet (depth) with sharp vertical edges protruding above the ground surface by about 4-6 inches adversely contributed towards causing heavy damage to the tires when the aircraft rolled over those at high speed.

The Aircraft Accident Investigtion Group of Bangladesh (AAIGBD) reported the first officer (36, CPL, 2,437 hours total, 1,762 hours on type) was pilot for the first ILS approach to runway 14 and initiated a go around upon reaching the decision height due to not being able to establish visual contact with the runway. The aircraft joined the missed approach procedure and positioned for another approach, the captain (40, ATPL, 12,000 hours total, 11,780 hours on type) was now pilot flying. The aircraft performed another ILS approach to runway 14. About 52 seconds after descending through 1000 feet AGL the crew sighted the approach lights of runway 14 in moderate to heavy rain in 10-11 knots cross wind. The crew was informed the runway was wet. The crew continued the approach and touched down to the right of the runway center line 576 feet past the runway threshold, the right hand main gear touched down first, the bank angle was about 15 degrees to the right. After rolling 786 feet the right main gear contacted went off the paved surface onto grass. The aircraft turned left now tracking parallel to the runway, rolled 1536 feet parallel to the runway, the right main gear about 6-7 feet off the paved surface of the runway. The AAIGBD wrote: "During this time, the right main gear wheels overran crashing about nine concrete cable laying pits, covered with iron-sheets, each having about 5 feet (length) x 4 feet (width) x 2 feet (depth) dimension. At this time, all the six (6) right main landing gear wheel tires were assumed to have been largely damaged and torn into fragments. The outer rear wheel drum of the right gear was found broken into a few pieces. The right main landing gear of the aircraft, thereafter, with broken wheel rim and devastated tires reverted back on the runway surface."

The aircraft returned onto the runway center line over the next 5000 feet of roll, subsequently joined high speed turn off H and stopped near the end of the taxiway short of taxiway S.

The AAIGBD described the damage: "During the whole process of aircraft landing roll, huge amount of wheel debris and brake assembly parts those got detached from the wheel assembly into pieces, were found scattered along the path described by the aircraft covering a large area of runway and grassy mud. Naked wheel rims were found making half to one inch deep cut marks all along on the runway and high speed taxi surfaces covering a distance of about 6500 feet. Post occurrence inspection of the aircraft revealed that the entire right wheel well, the surrounding airframe and even the right engine exhaust area were partially and wholly covered with grassy mud. The aircraft inspection by the investigating team also observed minor bent to some degrees of the right inner flap of the aircraft with grassy mud deposition around the flap hinges."

The aircraft also caused damage to the runway structures: "About nine wiring concrete pits of about 5 feet (length) x 4 feet (width) x 2 feet (depth) dimension, lying along the RWY right edge in the grassy mud area, were partially or largely broken and damaged; The exposed rims of the broken Tires cut through about 5000 Feet of the RWY surface with 2 Inch X ½ Inch marks."

The AAIGBD analysed:

While the visibility remained marginal, but above the limiting bracket, the aircraft, according to the DFDR readout, flew perfectly towards the centerline with a minor d-crab, catering for the incoming wind of speed 8-8.5 kts from the right. According to the deliberation by the flight crews and the DFDR & CVR analysis, it was revealed that the RWY was sighted by the PIC and followed by the FO just prior to Minima at 135-145 feet AGL. Soon after, he PIC disconnected the AP at 135 feet AGL and started flying the aircraft manually. Although landing clearance was given by the tower controller, there was no response from the aircraft for landing. Furthermore, the tower controller asked if the flight crews have sighted the RWY, but there was no response from the flight crews

The PIC flew the aircraft manually in order to maintain its d-crab profile for a while and thereafter to align the aircraft properly with the RWY centerline with the aircraft right wing slightly dipped down to cater for the cross wind and simultaneously applying the left rudder to counteract the aircraft drift. During this process, the aircraft went slightly below the glide slope with its longitudinal axis remaining about 5 degrees starboard of the RWY longitudinal axis.

Apparently, the rearmost outer wheel of the right landing gear touched the RWY surface well short of the RWY touch down zone and on to the right edge of the RWY veering the aircraft to right towards the right RWY edge and even beyond.

Once the right landing gear of the aircraft with its all six wheels were on the grassy mud, most damages to the wheels took place due to hitting the concrete pits. At least four out of six tires were fragmented into many pieces, the outer rearmost wheel rim got broken and considerable damage occurred to the whole wheel and associated brake assemblies.

While interrogating the flight crews, the investigation team learnt that although the pilots appreciated that the aircraft landed on the right edge of the RWY, neither of the flight crew could appreciate that the right main landing gear of the aircraft left the concrete surface and rolled along the muddy surface and thereafter overran nine pits causing severe damages to the wheels. It was only when the aircraft came out of the grassy mud, on to the concrete surface again with bare and broken rim cutting the RWY surface and the aircraft was juddering mildly, the FO realized and advised PIC that the aircraft right wheel tires may have given up (burst).

The Investigation Team, hereby analyses that the Pilot action by the PIC immediately after disconnecting the AP was not adequately coordinated to ensure that the aircraft touches down approximately at the „touchdown zone‟ and as close to the centerline of the RWY as possible.

The Investigation Team also noted that following a missed approach at the first approach, the flight crew, rather rapidly, initiated the second approach, which could have been delayed for the weather to clear up and thereafter, landing could be made in an improved weather condition.

The AAIGBD analysed that the tower was unable to see the aircraft during landing and remained unaware of the runway excursion too. Only another aircraft landing about 2 minutes later made tower aware of debris laying at the right hand side of the runway. An immediate runway inspection found evidence of the runway excursion. As TG-321 had stopped on the high speed turnoff it was clear TG-321 had suffered the runway excursion, tower dispatched emergency vehicles to the aircraft.

Related NOTAM:
A0233/18 NOTAMN
Q) VGFR/QMXLC/IV/NBO/A/000/999/
A) VGHS B) 1807240920 C) 1807261200 EST
E) TWY H SHALL REMAIN CLSD DUE TO DISABLE ACFT ON THE TWY

Metars:
VGHS 240800Z 15004KT 2000 TSRA BKN009 FEW025CB OVC090 26/25 Q1001 TEMPO +TSRA=
VGHS 240730Z 13004KT 2000 TSRA BKN009 FEW025CB OVC090 26/25 Q1002 TEMPO +TSRA=
VGHS 240700Z 00000KT 2000 TSRA BKN009 FEW025CB OVC090 26/25 Q1001 TEMPO +TSRA=
VGHS 240630Z 23007KT 2000 TSRA BKN009 FEW025CB OVC090 26/25 Q1002 TEMPO +TSRA=
VGHS 240600Z 21008KT 3500 RA BKN009 FEW025CB OVC090 28/25 Q1002 TEMPO TSRA=
VGHS 240530Z 14012KT 4000 HZ BKN010 FEW025CB BKN100 31/26 Q1002 TEMPO TSRA=
VGHS 240500Z 14008KT 4000 HZ BKN010 FEW025CB BKN100 31/26 Q1002 TEMPO TSRA=
VGHS 240430Z 15004KT 4000 HZ BKN010 FEW025CB BKN100 30/26 Q1002 TEMPO TSRA=
VGHS 240400Z 11006KT 4000 HZ BKN010 BKN100 30/26 Q1002 TEMPO RA=
VGHS 240330Z 12007KT 3500 HZ BKN010 FEW025CB BKN100 29/26 Q1003 TEMPO TSRA=
VGHS 240300Z 11006KT 3500 HZ BKN009 FEW025CB OVC090 29/26 Q1003 TEMPO TSRA