Wellington International Airport is the third busiest airport in New Zealand with an average of 250 daily flights and six million passengers a year. With an increase in travellers to and from the region, the use of larger aircraft from key partner airlines was inevitable. Therefore, the airport wanted to estimate the expected instances of differing water film depth on the runway based on local weather patterns and runway design and drainage characteristics. Differing runway water depths impact aircraft landing and takeoff performance due to the risk of aquaplaning.
A desktop study was undertaken to evaluate the drainage performance of the airport's grooved runway to ascertain the risk of aquaplaning during landing and take-off. This was to be assessed in accordance with International Civil Aviation Organisation (ICAO) standards.
Our extensive experience in skid resistance management of roads and runways meant we were uniquely placed to confirm the water drainage adequacy of Wellington’s main runway. We were solely responsible for the investigation, including detailed report preparation and communicating this to Wellington International Airport Limited. Analysis revealed that, even during extremely high rainfalls, there was less than a 2% chance that ICAO’s guideline of 3mm for maximum allowable runway surface water depth could be breached in any one year.
These findings were obtained using a spreadsheet based application written in-house to allow calculation of the required rainfall density to achieve a specified water film depth. This application accounted for the longitudinal and transverse slope of the runway as well as the dimensions and spacing of the runway surface grooves.
The application was used to calculate 10-minute rainfalls, as opposed to hourly, which allowed more accurate estimation of expected return periods for the runway surface water depths investigated.
We determined that Wellington International Airport’s runway had excellent drainage properties which, in theory, would result in very rare instances where surface water depth significantly impacted aircraft performance. Following this advice, Wellington International Airport Limited was able to use this information in discussions with key stakeholders, which resulted in detailed aircraft testing of the Airbus A350 and subsequent aircraft introduction.