Tom Allett joined Munich Airport’s friction testing team for a demonstration of its summertime duties.
WHILE FRICTION testing teams are always in demand during the winter months, it’s worth remembering that these important safety operations continue all year round. I was able to join Munich Airport’s Airside Operations team for a demonstration run on June 6, and saw firsthand what their work involves.
Munich has three Saab 9-5 alternative fuel sport sedans to call upon for friction testing and they are fed by the airport’s bioethanol gas station which opened in November 2007. Each vehicle is powered by a mixture of 85% bioethanol and 15% gasoline, thereby adding to the airport’s ‘green’ credentials.
To gather the necessary braking action data, all Saabs are equipped with the Scandinavian Airport and Road Systems AB (SARSYS) product from Sweden.
Built into the rear of the vehicle the technology is centred on a measuring wheel which is mechanically geared to one of the car’s rear main wheels. The measuring wheel’s gear ratio is such that when it is lowered from its stored position into contact with the paved surface it cannot follow the runway surface freely like the car’s four main wheels do, but instead, is forced to roll with a fixed slip ratio.
The friction it meets against the runway surface, combined with the weight on the measuring wheel, creates forces on that wheel which are continuously recorded by its electronic sensor system. The data collected by the sensors is processed by its computer system to produce a friction coefficient, often referred to as a friction number, which is continuously calculated for the duration of the run. The results are delivered in the form of a graph marked on a thin strip of paper that emerges from the system’s control console located at dashboard height immediately to the right of the driver’s position. The results of the test run, with the aid of a GPS system, are also transmitted direct to Munich’s air traffic controllers and the airport’s own airside ops office via a radio link, giving them the vital real time information that the pilots need. The friction data is of course delivered in accordance with ICAO standards and requirements.
During the summer, the build up of rubber deposits from aircraft tyres are the main reason for checking the runway’s friction conditions and at Munich it is standard practice to measure the paved surface’s coefficient at least once a month. However, these same vehicles are also used to carry out visual runway inspections that enable the ops team to check for Foreign Object Debris (FOD) or even ‘flag up’ any damage to the runway’s surface.
For friction testing purposes, one of the Saabs is able to deploy a film of water from a 500 litre tank located where the car’s rear seats would normally be. Unfortunately, at the time of our demonstration run, the car with the water tank was under repair, the temperature was hovering at around 26° Celsius and the runway was dry. Under those conditions, a real friction test without water would simply have destroyed the measuring tyre. Nevertheless, it was decided to go ahead with the patrol for demonstration purposes.
Air traffic control cleared us to enter the taxiway parallel to the southern runway and we proceeded down to the 08 right holding point and stopped adjacent to a Boeing 737 that was about to depart. After it started its take-off run we were cleared by the tower to enter the runway, and maintained a safe distance approximately in its eight o’clock position, well clear of its jet-blast area, as we accelerated along the runway. The airliner soon left us behind, climbing out in front of us in a matter of seconds.
On the day it was just a bit of ‘fun’ for my benefit, but every other time it is for real; just another one of those vital safety operations that takes place behind the scenes.