Singapore A333 at Yangon on May 21st 2014, temporary runway excursion on landing

Last Update: November 20, 2017 / 14:33:28 GMT/Zulu time

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Photo of Singapore Airlines 9V-STS, Airbus A330-300 — Singapore Airlines 9V-STS, Airbus A330-300 (Photo credit: Prayitno/more than 2.5 millions views: thank you! / Flickr / License: CC by)

Incident Facts

Date of incident
May 21, 2014

Classification
Incident

Airline
Singapore Airlines

Flight number
SQ-998

Departure
Singapore, Singapore

Destination
Yangon, Myanmar

Aircraft Registration
9V-STS

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

Airport
Yangon International Airport, Yangon

Airport ICAO Code
VYYY

A Singapore Airlines Airbus A330-300, registration 9V-STS performing flight SQ-998 from Singapore (Singapore) to Yangon (Myanmar) with 252 passengers and 13 crew, landed on Yangon's runway 21 in heavy rain but veered off the runway with its right main gear about 2000 feet down the runway at about 09:16L (02:46Z) and was steered back onto the runway about 4000 feet down the runway. The aircraft came to a stop on the runway with two main gear tyres damaged and was towed to the apron.

The airport was closed for about 30 minutes as result of the occurrence.

Passengers reported the aircraft touched down very hard.

A replacement Airbus A330-300 registration 9V-STM performed the return flight SQ-997 with a delay of 6:45 hours.

On May 28th 2014 the French BEA reported in their weekly bulletin that the aircraft veered off the paved surface of the runway and returned onto the runway, the excursion being about 670 meters/2000 feet long. There were no injuries. The aircraft sustained a deflated #7 tyre and damage to the innermost flap canoe fairings on the left and right side in addition to the loss of the green hydraulic system. Singapore's AIB is investigating the serious incident.

On Nov 20th 2017 Singapore's AIB released their final report without a formal conclusion to the probably causes of the serious incident and released following discussion instead:

When the aircraft was below 100 feet and just prior to the flare, the aircraft began to drift to the right. The Co-pilot and FO called out to the PIC to go to the left. The PIC also heard a “Dual Input” aural voice message9 and the Co-pilot called for a go-around just before the aircraft touched down on the runway.

By urging the PIC to go to the left, the Co-pilot and FO had recognised that the aircraft’s approach to the runway had become unstabilised. However, the PIC probably had not recognised this situation yet. By the time he heard the “Dual Input” aural voice message and the Co-pilot’s call for a go-around, the aircraft was below 20 feet and was about to touch down. It was still possible to execute a go-around, but the PIC elected to land the aircraft and then to align the aircraft with the runway centreline.

While it is a matter of judgment call on the part of a pilot as to whether he should go around or proceed to land when the aircraft was about to touch down on the runway, this incident highlights the preferable option of a go-around when the approach has become unstabilised.

Runway Excursion

Just before the aircraft touched down, both the PIC and Co-pilot were giving opposite roll inputs through their control side sticks. The net roll input was rightwards most of the time.

The practice of two pilots applying inputs into the control side stick is not in accordance with the aircraft manufacturer’s standard operating procedures nor the operator’s training. The Co-pilot’s left roll input was likely an attempt on his part to help correct the aircraft’s right drift, having realised that the PIC had not applied sufficient correction.

This net rightwards input for the roll allowed the aircraft to continue drifting to the right just prior to the touchdown. The right drift led to the aircraft’s touching down near the right edge of the runway. The momentum of the aircraft kept the aircraft moving towards the right, leading to its excursion from the runway.

Side stick handling

As mentioned in Footnote 2 in paragraph 1.1.9, there could be a tendency on a pilot’s part to over-adjust with side stick inputs, which could lead to an oscillatory effect. Such a tendency could be due to the way the side stick is held. Holding the side stick too tightly could make it difficult to input just the right amount.

As mentioned in paragraph 1.1.10, the aircraft had already drifted to the right of the runway centreline at the time of the aircraft’s flaring. The PIC recognised the need to realign the aircraft with the runway and kicked the left rudder to bring the aircraft back to the runway centreline with the intent of brining the aircraft back to the centreline. However, he also applied a right roll input, which had the effect of allowing the right drift to continue. This could have been an instinctive input as a result of de-crabbing training (a left rudder input to be coupled with a right roll input and, conversely, a right rudder input to be coupled with a left roll input). The PIC should preferably have rolled the aircraft to the left and flown the aircraft back to the centreline before de-crabbing. However, it is doubtful whether there was enough time for this manoeuvre, given that the aircraft was less than 20 feet from the ground. It therefore cannot be overemphasised that a much preferred option is to always go around whenever an approach has become unstabilised.

Runway shoulder

Between the points where the aircraft exited and re-entered the paved runway surface, the surface of the shoulder that abutted the runway was not flush with the surface of the runway and was also uneven. This condition of the shoulder did not seem to meet the recommended practice spelt out in paragraph 3.2.4 of Annex 14 Volume 1.

The captain (60, ATPL, 16,317 hours total, 1,432 hours on type) was pilot flying, the first officer (40, ATPL, 12,505 hours total, 45 hours on type, named "Co-Pilot" in the report, first officer by AVH) was pilot monitoring. Another first officer (40, ATPL, 5,545 hours total, 885 hours on type, named FO by the report, observed by AVH) occupied the observer's seat.

The SAIB reported the captain disconnected the autopilot at 1100 feet AGL, the crew became visible with the runway at about 800 feet AGL. Approach control cleared them to land on Yangon's runway 21, the crew puzzled and expecting to be handed off to tower before landing inquired, approach control confirmed they were cleared to land and were to remain on this frequency. At about 500 feet AGL the aircraft entered a rain shower, the wind screen wipers were engaged, the crew was able to maintain visual contact with the runway. The left crosswind began to shift and vary in speed. At about 100 feet AGL the left cross wind reduced from 20 to 10 knots. The captain therefore reduced the crab angle and rolled the aircraft to the right to correct for the reduced left drift, but obviously overcorrected, so that the aircraft began to drift to the right of the runway center line at about 50 feet AGL. Both First Officer and Observer called to turn left, the first officer began to provide left roll inputs with the captain still producing right inputs causing a "dual control" announciation at about 20 feet AGL. The first officer called for a go around, the captain however continued the approach. The aircraft touched down with the right main gear about 26 meters to the right of the runway center line (5 meters within the right runway edge, runway width 61 meters). One second later the right main gear departed the right hand edge of the runway. The captain applied left rudder, the aircraft returned onto the runway after the right main gear rolled over soft ground for about 610 meters and the left main gear rolled over soft ground for about 300 meters. The crew received a green hydraulic reservoir low quantity indication and stopped the aircraft on the runway. The aircraft was towed off the runway.

Post flight examination revealed damage to the green hydraulic system disabling nose wheel steering, damage to the innermost flap fairing canoes on both left and right hand side, the left engine ingested mud and debris, several tyres received cuts, tyre #7 deflated.

Metars:
VYYY 210500Z 13003KT 6000 BKN012 FEW015CB OVC090 25/23 Q1008 CB W
VYYY 210430Z 14003KT 6000 TS BKN012 FEW015CB OVC090 25/23 Q1008 CB W
VYYY 210400Z 03005KT 5000 TSRA BKN015 FEW018CB OVC090 24/24 Q1008
VYYY 210330Z 14004KT 5000 TSRA BKN015 FEW018CB OVC090 24/24 Q1009
VYYY 210300Z 22010G20KT 2000 TSRA BKN010 FEW018CB OVC080 27/27 Q1009
VYYY 210230Z 06005KT 7000 FEW018 FEW020CB SCT110 29/25 Q1008
VYYY 210200Z 08005KT 7000 FEW018 FEW020CB SCT110 27/24 Q1008
VYYY 210130Z 12003KT 7000 FEW018 FEW020CB SCT110 27/24 Q1008
VYYY 210100Z 10003KT 6000 SCT015 FEW020CB SCT110 26/25 Q1008
VYYY 210030Z 09003KT 6000 SCT015 FEW020CB SCT110 26/25 Q1007
VYYY 210000Z 05003KT 6000 SCT015 FEW020CB SCT110 25/23 Q1007
VYYY 202330Z 09003KT 6000 DZ SCT015 FEW020CB SCT110 25/23 Q1007
VYYY 202300Z 12003KT 6000 BKN015 FEW020CB BKN110 25/23 Q1006
VYYY 202230Z 12003KT 6000 SCT015 FEW020CB 25/23 Q1006