On 9 January 2020, a Fokker 100 (VH-NHY) being operated by Network Aviation for Qantas Link on a scheduled domestic passenger flight from Perth to Newman overran the wet destination landing runway by 70 metres after touchdown in the presence of both a strong crosswind and moderate rain. There were no occupant injuries and only minor aircraft damage resulted.
An Investigation into the accident was carried out by the Australian Transport Safety Bureau (ATSB). Relevant aircraft flight data was available in support of the Investigation.
It was noted that the Captain, who was acting as PF for the sector, had a total of 5,594 hours flying experience of which 1,963 hours were on type. The First Officer had a total of 2,920 hours flying experience of which 182 hours were on type.
The flight under investigation was the first of the day. The crew pre-flight briefing included a review of the forecast destination weather conditions which included heavy rain and a crosswind gusting up to 25 knots. The Captain decided to act as PF and loaded additional fuel to allow for a possible diversion to Port Headland, an approved alternate which took the aircraft up to MLW (maximum landing weight). The available information included the fact that the recorded cumulative rainfall at the destination airport was almost 9 cm. The Captain was familiar with operations into Newman but it was only the second time there for the First Officer.
Destination weather obtained en route was in line with the forecast already noted. The Captain stated that because of the potential for windshear during final approach, it was decided to make a flap 25 approach with speed brakes extended in place of the usual flap 42 approach thereby accepting an increased VAPP of 153 KIAS. The Captain stated that as they operated regularly to Newman, the required landing distance had not been calculated as they knew that aircraft could land there at MLW on both a wet and a dry runway. Nearer to destination, the AWIS (Automatic Weather Information Service) report was obtained and similar except for the mean wind direction backing slightly and the 2,072 metre-long 30 metre-wide runway 05 was confirmed for landing.
The forthcoming approach was discussed in respect of the possibility of windshear, turbulence and the likely significant crosswind component, but rainfall rate and the potential for water contamination or reduced braking effectiveness on the un-grooved runway were not discussed. A subsequent check of the AWIS gave visibility reduced in rain and the Captain commented that “the reduced visibility was likely related to a rain shower”.
FDR data showed that the approach was within the required stabilised approach criteria and airspeed fluctuations typical of gusty conditions. On reaching the applicable DA (the type of approach flown was not recorded) just as the First Officer was beginning to state ‘no contact’ the Captain called runway in sight and continued the approach. The Investigation found that “at the time that the Captain announced that the runway was in sight, the aircraft was 3,400 metres from the runway threshold, which was the required visibility for the approach”.
Both pilots stated that during the approach the rainfall was of a moderate intensity whilst the Aerodrome Reporting Officer (ARO) stated that there had been “a slight increase in rain intensity just prior to the landing” which made it “moderate rain”.
A “positive” touchdown occurred at, or slightly before, the TDZ at 154 KCAS with a 5 knot tailwind component. Eleven seconds after landing, at which point recorded flight data showed that braking effectiveness had reduced and then remained low for most of the remaining time on the runway, the Captain requested the First Officer to assist on the brakes. In the Captain’s opinion, aquaplaning has occurred and approximately 20 seconds after touchdown, the “aquaplaning response technique”, which involved reducing manual brake pressure and stowing the thrust reversers, was applied but to no effect and maximum reverse thrust was applied and deceleration then increased as the aircraft approached the end of the runway. Once off the runway, the aircraft came to a stop after 70 metres, still within the RESA.
All occupants subsequently left the aircraft using the front stairs and were then taken to the terminal. A visual examination of the aircraft found some deep scratches on the tyres and minor damage to some landing gear components both resulting from the abrasive and loose surface of the RESA.
It was noted that the most recent maintenance carried out on the Newman runway surface had been completed in June 2018 and had involved retexturing and excess rubber removal after an audit by the safety regulator, the Civil Aviation Safety Authority (CASA), had found that the bitumen which holds the asphalt aggregate together was seeping up to the surface in the TDZ at both ends of the runway.
A routine runway friction test designed to assess the condition of both the microtexture and the macrotexture of the surface was carried out in March 2019. This found that the macrotexture (which affects how fast water can escape from the surface in the absence of grooving) was frequently below the maintenance planning level and in places below the allowable minimum friction levels although when averaged over 100 metre stretches the lowest friction measurements did just meet the maintenance planning level. However, it was noted that the applicable standards had no requirement for, nor did they specifically permit, averaging of friction measurements in this way. However, the same tests performed a year later (after the investigated event) did not show any deterioration.
Prior to the landing, the ARO had, as required, inspected the runway and stated that they recalled having found “a significant amount of standing water on the grass strips on either side of the runway (but) the main runway surface clear of any noticeable standing water” and that this had continued to be the case as the rain continued after the overrun.
The Investigation noted that although there was no comparable CASA publication, FAA Safety Alert for Operators (SAFO) 19003 ‘Turbojet Performance on Wet Runways’ suggested that “whenever there is likelihood of moderate or greater active rain on a smooth (ungrooved) runway, or heavy rain on a grooved or porous friction course runway, landing distance calculations should be done assuming the surface is contaminated".
In respect of Company operations on wet runways, whilst the weather briefing section of the Flight Administration Manual “indicated that the possibility of runways being contaminated at the departure and destination airports should be considered during the planning process” and the Company expressly prohibited operations on contaminated runways, no guidance was provided on how pilots could determine if a runway was contaminated and, in particular, “moderate or heavy rain were not identified as possible runway contaminants”.
When advice was sought from the operator on how their flight crew were expected to assess whether a runway was contaminated, it was stated that they “should check NOTAM’s for any published runway unserviceability prior to departure” and “during flight, they should monitor the AWIS broadcast” despite the fact that this broadcast does not include any reference to standing water.
The Captain’s decision to make a flap 25 approach rather than the normal flap 42 one because of the possibility of windshear was considered against relevant Aircraft Operating Manual (AOM) content which stated that “flap 42 should be used when landing on contaminated runways or runways with reduced braking action”. On the other hand, in respect of windshear on approach, the AOM encouraged the use of flap 25 in conjunction with an increased VAPP only “if a safe approach and landing was thought to be feasible” and recommended considering an increased landing distance when an increased VAPP was used.
The Findings of the Investigation only identified one Contributing Factor which was “the combination of the approach speed required by the prevailing wind conditions and the poor braking effectiveness in the wet conditions (which) resulted in the aircraft overrunning the runway”.
However, four Factors that increased risk were identified as follows:
- During the flight, the potential for the heavy or moderate rainfall to significantly impact the landing distance was not recognised by the flight crew and therefore not considered as a threat.
- Despite technical examination of the runway identifying areas requiring maintenance to maintain the surface friction, no corrective action was taken.
- The operator's documentation required crew to consider contamination of runways at the departure and destination airports. However, the provided definition and guidance did not include the means to identify water contamination from active rainfall. [Safety Issue]
- CASA advisory publications did not include information regarding the potential for reduction in braking performance resulting from active moderate or heavy rainfall. [Safety Issue]
Safety Action known to have been taken whilst the Investigation was in progress was noted as having included the following:
- On 31 January 2020, Network Aviation issued a Flight Standing Order which required flight crews to plan for an alternate on runways less than 2,200 metres in length when there is a possibility of wet runway and a crosswind component greater than 20 knots. This order was accompanied by memorandum containing detailed explanations for determining moderate and heavy rainfall and the effect on landing distance required for wind corrections in wet and dry conditions. A second Flight Standing Order was also issued the same day which banned an approach (unless a greater emergency exists) to uncontrolled aerodromes where moderate or heavy rain is reported or observed.
- In October 2020, the CASA published an update to the CAAP 235-05 Section 3 on Landing Distance which included guidance on landing in very wet conditions including a reference to the FAA SAFO 19003 where it identified moderate active precipitation and ungrooved runways as being “risks to landing performance”.
On the basis of the findings of the Investigation, the ATSB formally documented a Safety Message as follows:
Active precipitation, particularly moderate to heavy rainfall, is one of many factors that can influence the stopping distance of an aircraft. Water on a runway that is not grooved can significantly reduce the ability of the aircraft to slow down. In wet weather, additional conservatism is encouraged when calculating the required landing distances.
Operators and pilots are encouraged to review the latest guidance and tools available in relation to maintaining safety on runways and the factors that cause runway overruns.
The Final Report was released on 1 September 2021. No Safety Recommendations were made.