Virgin Australia B738 at Darwin on Dec 6th 2016, temporary runway excursion on landing
Last Update: May 15, 2019 / 14:14:50 GMT/Zulu time
Australia's ATSB reported the occurrence was rated a serious incident, an investigation has been opened after the aircraft veered off the runway in gusty wind conditions and received minor damage as result. Two investigators were dispatched on site.
On May 15th 2019 the ATSB released their final report concluding the probable causes of the serious incident were:
- After passing the decision height for the approach, the aircraft drifted under the influence of a slight crosswind and landed 21 m to the right of the runway centreline.
- Due to heavy rain, darkness and limited visual cues, the flight crew did not detect the aircraft’s deviation from the runway centreline prior to landing.
- The absence of centreline lighting and the 60 m width of runway 11/29 at Darwin result in very limited visual cues for maintaining runway alignment during night landings in reduced visibility. [Safety issue]
Other factors that increased risk
- Category I runways that are wider than 50 m and without centreline lighting are overrepresented in veer-off occurrences involving transport category aircraft landing in low visibility conditions. The installation of centreline lighting on wider category I runways is recommended but not mandated by the International Civil Aviation Organization Annex 14. [Safety issue]
- Virgin Australia did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility. [Safety issue]
- The En Route Supplement Australia (ERSA) did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility. [Safety issue]
- While the aircraft was on descent, the airport’s primary anemometer failed due to a lightning strike. Although there were windsocks and a second, test anemometer at the airport, the reliability and timeliness of the wind information that the controllers could provide to flight crews was temporarily degraded.
- Although air traffic services broadcast details of an amended aerodrome forecast (TAF) for Darwin issued at 2207, the flight crew were not made aware of a subsequent amended TAF issued at 2237. However, the flight crew were provided with multiple updates of current weather conditions prior to landing at 2302.
- Because they were unsure what had occurred, the flight crew did not report the possibility of a runway excursion to air traffic control until 29 minutes after it occurred. This delayed the response by the airport operator and air traffic control to ensure that the runway was safe for subsequent operations.
The ATSB analysed:
During the landing on runway 29 at Darwin at night, the aircraft touched down 21 m to the right of the runway centreline while tracking about 3° to the right. Apart from the sudden degradation of visibility, other aspects of the landing (in terms of the aircraft’s configuration, airspeed, distance down the runway and descent rate) were normal. Soon after touching down, the right main gear departed the sealed surface.
The runway excursion (veer-off) was due to the aircraft deviating from the runway centreline during the final stages of the final approach. There were no aircraft serviceability issues. The crosswind was not sudden or strong enough to be significant under most circumstances.
In summary, the main visual cues the flight crew of VH-VUI had in the last few seconds prior to touchdown (from 100 ft above ground level) were the runway edge lights. It was during this period that the aircraft started and then continued to deviate from the runway centreline.
It appears that the aircraft started drifting right under the influence of an increasing (although light) crosswind, and a small amount of right bank. However, deviations occur during manual control for a number of reasons, and the important aspect in this case is that the deviation was not detected and corrected. The deviation occurred in turbulent conditions, which required continuous corrections to the aircraft’s attitude and flight path, and there were insufficient external visual cues during this high workload period for the flight crew to effectively detect the deviation and make appropriate adjustments. The available evidence did not indicate fatigue, medical issues or distraction affected the flight crew’s performance.
A significant factor reducing the effectiveness of the visual cues in this case was the wider than normal width of the runway (60 m compared to the much more common 45 m), and the corresponding increased distance between the two rows of runway edge lights. As indicated by simple graphical representations (see Appendix A), it is more difficult to detect a deviation when approaching a wider runway compared to a narrower runway. By the time a deviation is identified on a wider runway, the momentum of the lateral movement may be such that the deviation is difficult to correct prior to touchdown.
More importantly, the rate of veer-off occurrences due to misalignment during late final approach is much higher at 60 m wide runways than 45 m wide runways. All of these occurrences have taken place at night in situations where rain or other environmental factors reduced other visual cues.
This problem has been recognised for a long time, with the International Civil Aviation Organization (ICAO) and regulatory authorities recommending the use of centreline lighting on runways wider than 50 m that are used for Category I ILS approaches.
When the aircraft touched down the flight crew were aware they had landed to the right of the centreline but did not fully comprehend the extent of the deviation and the rate of drift. The captain applied corrective control inputs but, by the time the situation was apparent, was unable to prevent the right main landing gear departing the sealed surface of the runway.
The amount of corrective control input applied by the captain was influenced by the potential to lose control on the wet runway, in combination with the advice from the first officer who thought that the aircraft was clear of the runway lights.
The captain delayed the application of reverse thrust after landing until the aircraft was established on the runway. This action probably helped prevent further excursion off the runway.
Given the extent of the deviation from the runway centreline at touchdown, and the time required to assess the situation, it was very likely the excursion would have happened regardless of the available traction. Traction was probably reduced to some extent after touchdown, and it may have slightly delayed the subsequent recovery back onto the runway. The ATSB notes that the outer 7.5 m of the runway was not grooved, and did not meet the relevant surface texture or friction requirements. Although not contributing factors to this occurrence, such problems could degrade aircraft control in future situations where an aircraft has significantly deviated from the runway centreline.
After the landing the crew were unsure whether the aircraft had left the runway. The flight crew discussed whether they had hit the runway lights. Based on the first officer’s perception of the situation, they thought that they had not.
There was no opportunity for ground crews to examine the aircraft and confirm a potential veer-off until the storm had cleared, but there remained a risk that following aircraft could be affected by debris on the runway, and having fewer runway lights available.
This occurrence indicates that it is important to be conservative after a potential veer-off occurrence. A timely report of the possibility that a veer-off had occurred, even if there was doubt, would have provided the airport operator and air traffic control with a better opportunity to ensure the runway was serviceable for other aircraft.
YPDN 061500Z 34002KT 9999 FEW035 SCT105 26/25 Q1009
YPDN 061430Z 34004KT 9999 VCSH FEW020 SCT065 BKN105 26/25 Q1009
YPDN 061400Z 31007KT 9999 VCSH FEW010 SCT020 BKN050 FEW020CB 26/25 Q1009
YPDN 061342Z 32011KT 5000 -TSRA FEW010 SCT020 BKN035 FEW020CB 25/24 Q1010 RETS
YPDN 061330Z 29015KT 2000 +TSRA FEW011 BKN020 BKN035 FEW020CB 26/24 Q1010
YPDN 061327Z 29016KT 2000 +TSRA FEW011 BKN020 BKN035 FEW020CB 26/25 Q1010
YPDN 061317Z 23009KT 7000 TSRA FEW018 SCT023 BKN045 FEW023CB 27/25 Q1010
YPDN 061300Z 25007KT 190V310 9999 -TSRA FEW018 SCT023 BKN060 FEW023CB 28/25 Q1009
YPDN 061230Z 31009KT 9999 VCSH FEW018 SCT035 BKN060 29/26 Q1009
YPDN 061200Z 32010KT 9999 -RA FEW018 SCT045 BKN060 30/26 Q1009 NOSIG RMK USE TAF FOR ARRIVALS AFTER 1230Z
YPDN 061130Z 29007KT 9999 FEW025 SCT035 BKN060 30/25 Q1008 NOSIG RMK USE TAF FOR ARRIVALS AFTER 1230Z
YPDN 061100Z 27006KT 9999 FEW025 BKN060 30/25 Q1008 NOSIG RMK USE TAF FOR ARRIVALS AFTER 1230Z
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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