Tapio Haarlaa / Application Team Leader / Vaisala / Helsinki, Finland

Aquaplaning poses a serious risk to aviation safety during heavy rain, and it is most frequent in the tropics. Aquaplaning It has been a contributing factor in some aircraft incidents and acci- dents, such as the Qantas Flight 1, - too much water on the runway? which skidded off the runway in Bangkok on 23 September 1999. Luckily there were no casualties, Aquaplaning is a phenomenon that can occur but 38 people were injured and the aircraft suffered some costly damage. when a layer of water builds up between the Accurate information on water level thickness on the runway could aircraft’s tires and the runway surface. It may help pilots to make better decisions on how to land safely. Until recently, result in a situation where braking action on the a comprehensive and reliable method for assessing the thickness of the wheel is not effective. water layer has not been available.

What can be done to avoid aquaplaning?

Aircraft can use its tire brakes, flaps, spoilers and reverse thrust to decel- erate its speed, for example. These

Singapore’s Changi Airport has established itself as a major aviation hub in the Asia Pacific. It has a capacity to handle 70 million passangers a year.

14 181/2009 methods are usually enough, but The project was first kicked off warning system is built around unexpected conditions during landing when the Civil Aviation Authority of a thorough understanding of the may result in their ineffective use. Singapore (CAAS), which provides runway topography, combined with As grooves across the runway air navigation services at Singapore water flow-off modeling. It computes surface help drain excess water, they FIR and Changi Airport, received and displays the estimated water may decrease the risk of a landing feedback from pilots on the need for layer thickness on runway zones aircraft ending up in an aquaplaning more precise and real-time informa- using a specific equation that takes situation. However, a gooved runway tion on the thickness of the water into account the precipitation values won’t completely eliminate the risk layer on the runway. and the flow-off value. in heavy rain. Although Changi Airport’s The flow-off value from the Information on water layer thick- runways are already designed to runway surface is based on empirical ness on the runway can be gathered ensure rapid water run-off, CAAS measurements on the runway using different methods. One option recognised that more could still be zones, performed prior to system is to take direct measurements using done. CAAS contacted Vaisala to find calibration. The flow-off values can runway surface sensors. However, a reliable way to measure water level be defined independently for each this method is not always very on the runway in real-time situations. runway zone. The precipitation reliable, as it is a spot measure- This was a completely new endeavor values are based on precipitation ment only, and does not account for for both parties, as there was no sensor measurements in each of the pooling or the runway’s character- existing solution available in the runway zones. Vaisala’s aquaplaning istics. market. warning system is patented. A more sophisticated approach The project started in November Installing the system requires a relies on modeling the ways in which 2007, and the new system - tailored comprehensive site survey of the the water flows off the runway. and developed for the needs of airport in question as well as a good Indirect measurement can be Changi Airport - was installed for understanding of the airport’s require- calculated based on rain intensity testing in December 2008. So far, the ments and the runway’s technical measurements and a runway surface results have been encouraging. details. Once these have been estab- analysis method called aquamapping. Explaining CAAS’ initiative in lished, suitable sensor locations can this project, CAAS’ Director of Air be identified and the system can be Singapore at Traffic Services Mr Ng Tee Chiou installed. After installation, the system the forefront of said: “CAAS constantly seeks innova- requires annual calibration, as runway development tive ways to improve operational conditions change due to normal wear efficiency. We believe in leveraging and tear or resurfacing, for example. Due to its tropical location, Singapore new technologies that will enhance is prone to heavy rain. This is one of the safety and efficiency of air traffic Moving forward the reasons why Singapore now leads operations. We hope that Vaisala’s the way in addressing safety risks water level measurement tool will Information on the thickness of the caused by aquaplaning. aid air traffic controllers to pass water layer on the runway in heavy on essential runway information to rain supports decision-making pilots, thereby boosting the level of and increases airport safety and flight safety.” efficiency. The next phase of the Singapore pilot project is to establish How does the warning the best working practices between system work? air traffic controllers and pilots regarding communications relating Instead of relying on simple but to aquaplaning. Sharing this critical rather unreliable spot measurements information in an efficient manner only, an intelligent aquaplaning can save both lives and money.

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