There are two main principles for measuring friction: dry and wet measuring. Dry measurement is used in winter or any other situation when friction values can be expected to be lower than normal. These situations can be for example rain, snow, slush, dust, etc. Wet measuring is called runway calibration and it’s used for checking the rubber build-up on the runway.
Winter / dry friction measurement
Measure when the meteorological service expect ice or snow. Hourly reports as a minimum and certainly whenever
there is reason to believe tlere has been change in the runway state. (A decelerometer or a diagonal braked vehicle should not be used in deep loose snow or slush as each can give misleading friction values)
Where to measure:
Measurement is done with a long line on each side of the center line, approximately 3m or that distance from the centre line at which most operations take place. Test speed 65km/h or 95km/h or lower when necessary.
Friction values in braking action:
|Mu||ICAO value||ICAO code||Measured snowtam decode|
|more than 0.40||GOOD||5||95|
|0.36-0.39||MEDIUM TO GOOD||4||94|
|0.29-0.26||MEDIUM TO POOR||2||92|
|less than 0.25||POOR||1||91|
Summer / wet measurement (runway calibration)
|Number of daily turbojet aircraft landing per runway end||Minimum friction survey frequency|
|Less than 15||Annually|
|91 – 150||Monthly|
|151 -210||2 weeks|
|Greater than 210||Weekly|
Friction level classification:
|Measuring speed||New Runway level||Maintenance level||Minimum level|
If the measuring results are:
- Below maintenance level 152m (500ft) or longer –> more frequent monitoring.
- Below maintenance level 305m (1000ft) or longer –> corrective actions and more frequent monitoring.
- Below minimum level 152m (500ft) or longer –> immediate corrective action.
- New runway average should not be below new runway level shown on the table.
- Painted areas: Below minimum 30m (100ft) or more –> immediate corrective action.
- Difference between dry and wet measurement greater than 40 –> immediate corrective action.
If you have any questions regarding the friction values, please don’t hesitate to contact us.