18 Sep 2018 - Report issued into VH-VOP 737-800 aquaplaning on landing
On 11 May 2015, a Boeing 737 aircraft, registered VH-VOP and operated by Virgin Australia International, conducted a scheduled passenger service from Sydney, New South Wales to Christchurch, New Zealand. Shortly after midnight, the aircraft landed on runway 29 at Christchurch. Runway 29 was shorter than the main runway at Christchurch. The aircraft landed within the required touchdown zone, using full reverse thrust, speedbrakes, and the autobrake system engaged the wheel brakes. Recorded flight data showed that the aircraft initially achieved, and at times exceeded the selected AUTOBRAKE 3 target deceleration rate. However, after crossing the runway intersection, the aircraft did not continue to decelerate as expected and the crew believed the aircraft appeared to slide or skid. In response, the crew overrode the autobrakes and applied hard manual braking while retaining full reverse thrust for longer than used in normal operations. The crew also corrected a minor directional deviation. The aircraft came to a stop about 5 m from the runway end. There were nil recorded injuries or aircraft damage.
Extracts of the report are given below but the full 71 page AustralianTSB report is available here
*** Updated 23 Nov 2020 ***
What the ATSB found
The ATSB found that, due to increased workload, the crew misperceived the runway surface conditions and believed it was damp when in fact it was wet. As there was no regulatory direction on how a damp runway was to be considered for aircraft landing performance purposes, the operator’s policy was to treat a damp runway the same as a dry runway. As a result, the crew established the aircraft’s landing performance based on a dry rather than a wet runway and the expected runway 29 landing performance was not achieved.
The ATSB also found that, several months prior, the operator had changed its policy whereby damp runways had previously been treated as wet runways.
Based on the crew’s observations and a review of the available recorded data, it was very likely that the surface conditions on the later part of the runway had degraded to the extent that they adversely affected the aircraft’s braking capability. It was also possible that the aircraft experienced viscous aquaplaning. However, the initial exceedance of the target deceleration rate, combined with the crew’s actions, likely prevented a runway overrun.
Further, a post-incident analysis of the flight data recorder by the aircraft manufacturer found that a 5 kt tailwind existed on final approach and landing. This also significantly affected the aircraft’s landing performance and further reduced safety margins.
Additionally, and along with the United States Federal Aviation Administration, the ATSB found that the 15 per cent in-flight safety margin applied to actual landing distances during landing performance calculations may be inadequate under certain runway conditions. In these conditions, additional conservatism is encouraged.
This incident highlights the adverse consequences of crew experiencing a high workload during critical phases of flight, including missing important information needed to determine an accurate landing performance.
In addition, runway surface condition and braking action reports (intended for the benefit of other pilots landing aircraft after them) can be subjective, and the terminology used to describe these can be inconsistent. Considerable efforts have been made by organisations such as the United States Federal Aviation Administration to address this issue with the introduction of the runway condition assessment matrix.
Flight data recorder (FDR) analysis
The aircraft was fitted with a FDR and following the incident, the data was downloaded by the operator and provided to the ATSB. The aircraft’s recorded data was also analysed by Boeing. The data showed the following (Figure 9):
Figure 9: Aircraft’s ground path and recorded data after crossing the runway 11/29 and 02/20 intersection.
Image shows the aircraft’s ground path (in yellow) and recorded data after crossing the runway 11/29 and 02/20 intersection (the zigzag yellow line on the last section of the runway was the result of flight data recording limitations). Source: Google earth, annotated by the ATSB
Boeing conducted simulations using the recorded data available in an attempt to characterise the amount of brake pressure applied and the runway conditions. While assumptions were made regarding the runway condition and commanded brake pressure, the results indicated that ‘good’ braking capability was initially achieved until the aircraft crossed the runway intersection. Between the intersection and the runway end, the aircraft’s braking capability significantly reduced. Deceleration throughout the landing was initially consistent with the characteristics of a wet runway and then consistent with a flooded runway after crossing the runway intersection. Boeing further stated that, since runway 29 was not grooved, if standing water was present between the intersection and runway end, the aircraft’s braking capability would have been reduced.
From the evidence available, the following findings are made with respect to the reduced braking effectiveness during landing involving a Virgin Australia International Airlines Boeing 737-800, registered VH-VOP that occurred at Christchurch Airport, New Zealand on 11 May 2015. These findings should not be read as apportioning blame or liability to any particular organisation or individual.
Safety issues, or system problems, are highlighted in bold to emphasise their importance. A safety issue is an event or condition that increases safety risk and (a) can reasonably be regarded as having the potential to adversely affect the safety of future operations, and (b) is a characteristic of an organisation or a system, rather than a characteristic of a specific individual, or characteristic of an operating environment at a specific point in time.
Definitions of the following headings are provided in the section titled Terminology used in this report.
Other factors that increased risk
The full AustralianTSB report is available here