Virgin Australia B738 at Christchurch on May 12th 2015, control issues during landing

Last Update: September 18, 2018 / 14:06:47 GMT/Zulu time

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Incident Facts

Date of incident
May 12, 2015

Classification
Incident

Airline
Virgin Australia

Flight number
VA-134

Departure
Sydney, Australia

Destination
Christchurch, New Zealand

Aircraft Registration
VH-VOP

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

Airport
Christchurch International Airport, Christchurch

Airport ICAO Code
NZCH

A Virgin Australia Boeing 737-800, registration VH-VOP performing flight VA-134 (dep May 11th) from Sydney,NS (Australia) to Christchurch (New Zealand), landed on Christchurch's runway 29 in rain at 00:15L (May 11th 12:15Z) but encountered water standing on the runway and hydroplaned before coming to a stop. The aircraft subsequently taxied to the apron.

Australia's ATSB opened an investigation into the occurrence rated an incident stating the aircraft suffered control issues when it encountered standing water and aquaplaning while landing on Christchurch's runway 29 arriving from Brisbane,QL (Australia) on May 11th at 12:15Z (May 12th 00:15L), the aircraft was stopped approximately 5 meters from the end of the runway.

Radar data show the aircraft arrived from Sydney at 12:15Z and confirmed the aircraft landed on runway 29 vacating the runway at the last exit. There was no flight scheduled to arrive from Brisbane within 9 hours before to 15 hours past the occurrence.

New Zealand's TAIC is investigating an occurrence, which appears to be quite similiar, see Incident: ANZ B733 at Christchurch on Mar 6th 2015, runway excursion on landing.

On Sep 18th 2018 Australia's TSB released their final report concluding the probable causes of the incident were:

Contributing factors

- Due to the crew experiencing increased workload, the crew misperceived critical landing information, which resulted in the aircraft’s landing performance being determined based on a damp (dry) runway rather than a wet runway.

- The runway surface conditions combined with the autobrake selection resulted in the aircraft exceeding the landing performance limitations for runway 29 for both the reported and actual wind conditions.

- Using the operator's Airport Analysis Manual to establish that the aircraft could land safely on runway 29 relied on the crew's judgement to determine the braking level required. While that judgement was consistent with the flight crew training manual, the Quick Reference Handbook indicated that a higher braking level than chosen was needed to meet the landing distance safety margin requirements.

- It was very likely that the amount of water on the later part of runway 29 resulted in less than 'good' braking action. Along with the possibility of viscous aquaplaning and despite the crew applying hard braking, this water resulted in a reduced braking capability.

- Several months prior to the incident, Virgin Australia Airlines/Virgin Australia International changed their policy on calculating landing performance for damp runways from referencing a wet runway to a dry runway. [Safety issue]

- There was no regulatory direction from the Civil Aviation Safety Authority on how a damp runway was to be considered for aircraft landing performance. [Safety issue]

- Virgin Australia Airlines/Virgin Australia International did not have a policy requiring crews to independently cross-check environmental information and landing performance calculations in-flight, removing an opportunity to detect crew errors. [Safety issue]

Other factors that increased risk

- The operator provided guidance on landing performance through an uncontrolled mechanism, which did not provide assurance that crews had read, understood and applied the critical information contained within that guidance.

- The flight following department did not highlight to the crew the changing weather conditions, which had the effect of minimising their landing options for Christchurch.

- The subjective nature of assessing runway surface conditions and braking action, increases the risk of incorrect landing performance determination.

- Civil Aviation Order 20.7.1B stipulated that a 1.15 (15 per cent) safety margin was to be applied to the actual landing distance for jet-engine aircraft with a maximum take-off weight greater than 5,700 kg. This safety margin may be inadequate under certain runway conditions, which increases the risk of a runway excursion. The corresponding guidance in Civil Aviation Advisory Publication 235-5(0) had not been updated to account for this. [Safety issue]

- The inherent complexity of re-calculating landing performance data in-flight using the operator’s Quick Reference Handbook increases the risk of errors, especially during times of elevated crew workload.

Other findings

- The operator's guidance was inconsistent with its policy for determining in-flight landing performance.

- Initial aircraft autobraking above the required deceleration rate, combined with the crew’s application of hard manual braking and delayed stowage of reverse thrust, likely reduced the risk of a runway excursion.

- The main landing gear brake pressure recording switch was faulty, therefore, the amount of brake pressure applied during landing was not recorded by the flight data recorder.

The ATSB reported that the Boeing was the second aircraft on approach to Christchurch, the first aircraft was an A320 however talking to ATC on a different frequency. Upon contacting Christchurch Approach the Boeing crew was told, runway 02 was in use, the runway was dry, and reported weather matched the preflight preparations. The A320 however was told a runway change was pending due to changing surface winds, it had started raining, runway 29 became active, the surface was dry. The ATSB wrote: "The A320 crew continued discussions with ATC regarding the changing weather conditions at Christchurch. The crew determined that, rain on the reported dry runway rendered it wet, therefore, they were unable to land at Christchurch due to performance restrictions and elected to divert to Wellington."

While the Boeing was descending towards Christchurch Approach told them that ATIS had changed stating: "quite a few changes from the previous, you want to have a listen". A minute later ATC cleared the flight to further descent to FL160, the crew acknowledged with "Velocity 160" (ATSB wrote: "inadvertently transposing their cleared flight level for their call sign"). The crew requested the surface winds which were reported from 250 degrees at 12 maximum 18 knots. The crew prepared for the revised approach, noticed weather ahead and requested a deviation around the weather.

About 4 minutes later ATIS changed again, the runway was now reported wet in light rain, ATC advised the crew of the changes, the crew therefore did not listen to ATIS again.

Another 4 minutes later the A320 changed to the same frequency and advised again they were diverting to Wellington. However, another aircraft, that had departed Christchurch, reported they had taken off runway 29 about 5-10 minutes earlier and the runway was damp, not wet.

Believing ATC had reported the runway damp the crew determined they could land on runway 29 (however, due to the wet surface they were one ton over weight for landing on runway 29). While the aircraft maneouvered to establish on the extended runway center line ATC advised that the rain had stopped and the winds were easing until they were reported calm just as the aircraft joined final approach. The captain, pilot monitoring, saw the runway surface, which did not appear to be reflective, and assessed the runway being damp.

The ATSB described the landing:

At 1214, the aircraft touched down on runway 29 within the touchdown zone. Immediately after, full reverse thrust was applied and the speedbrakes deployed.

During the landing roll, as the aircraft passed the runway 02/20 and 11/29 intersection (Figure 7), the FO reported that he did not receive the expected sensation of being restrained against the seat belt and shoulder harness and the aircraft did not decelerate as expected. The FO also indicated that it felt like the aircraft was sliding. In response, the FO made a call to the effect of ‘aquaplaning’ or ‘skidding’ and applied constant ‘hard’ (but not full) manual braking, overriding the autobrake system. The captain noted that there was a lot more surface water on that section of the runway than what was observed at the beginning of runway 29.

The captain assisted the FO with manual braking. Both crew reported that they could feel the rudder/brake pedals ‘pulsing’, which indicated the antiskid system was operating. The crew elected to keep reverse thrust deployed to assist with braking.

The FO reported that he was focusing on the red runway end lights and noticed the aircraft drift slightly right, which he then corrected to bring the aircraft back onto the centreline. The captain reported that, when reverse thrust was stowed near the runway end, there was enough surface water on the runway to create a wall of spray. The FO reported that the aircraft came ‘slowly sliding’ to a stop about 5 m from the runway end lights. The aircraft was then taxied to the terminal.

About 3 minutes after landing, ATIS ‘Bravo’ (B) was issued, where the runway-in-use changed to runway 02 and the reported surface conditions were changed to ‘damp’.

Following engine shutdown, the crew re-checked the landing performance data for a damp (dry) runway. They also considered the amount of water spray observed at the runway end and believed the surface conditions at that time were not damp. Soon after, the captain spoke to a ground engineer who had also observed the significant amount of water spray. The engineer stated that water seemed to pool in that area of the runway when it rained. The captain and FO had not previously been aware of any tendency for water to pool on that runway. The FO conducted a visual inspection of the aircraft’s tyres with an engineer to see if any reverted rubber was present; none was detected.

The ATSB reported the aircraft touched down at 138 KIAS (Vref40 135 KIAS), the autobrakes activated after touchdown at setting 3 and did achieve the deceleration target of 0.224G subsequently exceeding the target at 0.29G. When the aircraft slowed through 79 KIAS, shortly after crossing the runways intersection, autobrakes were disengaged and manual braking commenced but soon fell below the deceleration target. The first officer, pilot flying, applied hard braking with the captain assisting. Overall the deceleration rate achieved over the full length of the landing roll was 0.179 G. Reverse thrust was reduced to idle only when the aircraft slowed through 20 knots (normally 60 KIAS).

The ATSB analysed:

Crew’s actions prevented a runway excursion

According to the AAM, the aircraft was unable to land on runway 29 when wet. The QRH indicated that, for a wet runway with ‘good’ reported braking action, the actual landing distance was marginally less than the landing distance available with the actual reduced air distance and reference speed. However, the surface conditions on the later part of the runway likely resulted in less than ‘good’ reported braking action, which reduced the aircraft’s braking capability. Consequently, the aircraft was stopped about 5 m from the runway end. It was likely that the initial exceedance of the AUTOBRAKE 3 deceleration rate, combined with the crew's application of hard manual braking and retaining reverse thrust prevented a runway excursion.

With respect to damp runways the ATSB analysed:

Regulatory direction regarding damp runways

While the term ‘damp’ was used by air traffic service providers and airport operators internationally to describe runway surface conditions, it was not used by CASA or by major aircraft manufacturers for providing performance data. Consequently, there was no regulatory direction from CASA to operators on how a damp runway was to be considered for performance purposes.

Instead, it was the operator who determined if a damp runway was treated as dry or wet. In this case, the definition adopted by Virgin Australia Airlines/Virgin Australia International was based on operational requirements and that used the by European Aviation Safety Agency.

In addition, the term has been applied inconsistently among Australian operators. This is of particular concern since research has shown that a damp runway may not provide an equivalent braking surface as a dry runway. This increases the risk of an excursion as a result of overestimating an aircraft’s braking efficiency.

In addition the ATSB analysed:

Operator’s landing performance policy and guidance inconsistent

At the time of the incident, the operator’s policy stipulated that the AAM was to be used for determining landing performance. While it was recognised that the operator was in discussions with CASA regarding the CAO 20.7.1B changes, the policy differed from the guidance provided in the Virgin Australia Q and A. The Q and A indicated that the AAM was to be used pre-dispatch and the QRH used in-flight. However, it was not known if the inconsistency between the policy and guidance resulted in confusion among crews. Irrespective, CAO 20.7.1B allowed both the AAM (certified data) and QRH (advisory data) to be used to establish landing performance in-flight.

Further, during transition training for the incorporation of Virgin Australia New Zealand into Virgin Australia International, the New Zealand crews were instructed to use the AAM to determine their in-flight landing performance. This was considered an interim measure until the operator’s policy had been updated to reflect the CAO 20.7.1B changes. However, the Q and A guidance advised crews to use the QRH in-flight. While the crew of VOP were not aware of the Q and A prior to the incident, their transition training was consistent with the policy but contradicted the guidance.

The ATSB analysed the exceedance of the runway 29 landing performance:

Runway 29 landing performance exceeded

According to the AAM, with a wet runway surface, the aircraft’s actual landing weight was above the landing performance limit weight for both the reported and actual wind conditions by about 100 kg and 5.7 T respectively. Therefore, at the time of landing, the aircraft exceeded the AAM landing performance limitations for runway 29.

The captain assessed that the initial part of runway 29 was damp. A pilot who departed Christchurch about 30 minutes prior to VH-VOP (VOP) landing had also reported that the runway surface was damp rather than wet. However, the surface conditions were reported wet by ATC and the amount of water spray observed during the later stages of the landing indicated that this section of the runway at least was wet.

At the time of landing, the reported wind conditions from the automatic terminal information service indicated a 3 kt headwind, while the actual wind determined by the flight data recorder showed a 5 kt tailwind. Notably, the automatic weather station data was showing a change in the wind direction around this time and the automatic terminal information service issued shortly after landing indicated the wind was now variable.

The Quick Reference Handbook (QRH) landing distance charts provide a landing solution by taking into account braking selections. With AUTOBRAKE 3, as selected by the crew, for a wet runway (‘good’ reported braking action):

- For the reported wind conditions, the calculated actual landing distance was within the landing distance available. However, when the 15 per cent in-flight safety margin stipulated in the Civil Aviation Safety Authority (CASA) Civil Aviation Order (CAO) 20.7.1B was applied, the landing distance required exceeded the landing distance available.

- For the actual wind conditions, both the calculated actual landing distance and landing distance required exceeded the landing distance available (air distance of 305 m and reference speed plus 5 kt). However, when taking into account the reduced air distance and speed at touchdown established from the flight data recorder, the calculated actual landing distance was within the landing distance available, but the landing distance required exceeded it.

Therefore, to meet the CASA in-flight landing distance requirements, a setting of AUTOBRAKE MAX or MAX MANUAL would have been required. Landing performance calculations are designed to ensure the aircraft stops within the confines of the runway. By exceeding these requirements, the risk of an overrun event is increased.

Of significance, the QRH calculations also showed that the wet runway, 5 kt tailwind and additional effects from the runway surface conditions combined, increased the aircraft’s expected actual landing distance by about 12 per cent.

Metars:
NZCH 111330Z AUTO 36004KT 310V050 9999 NCD 09/08 Q0990 NOSIG
NZCH 111300Z AUTO 36004KT 300V040 9999 NCD 10/08 Q0991 NOSIG
NZCH 111230Z AUTO 14001KT 9999 -RA FEW070/// 12/09 Q0991 BECMG 24020G35KT
NZCH 111200Z AUTO 26008KT 220V290 9999 -RA SCT060/// BKN070/// 13/09 Q0993 BECMG 24020G35KT
NZCH 111130Z AUTO 36005KT 9999 SCT070/// OVC090/// 15/06 Q0992 NOSIG
NZCH 111100Z AUTO 04009KT 9999 BKN070/// 16/06 Q0992 NOSIG
NZCH 111030Z AUTO 04010KT 9999 OVC070/// 16/06 Q0992 NOSIG
NZCH 111000Z AUTO 05016KT 9999 BKN080/// 16/06 Q0991 NOSIG
NZCH 110930Z AUTO 06011KT 9999 FEW065/// BKN080/// 16/06 Q0991 NOSIG
NZCH 110900Z AUTO 05009KT 9999 BKN080/// 15/06 Q0991 NOSIG