Safer surfaces


Reducing and removing rubber deposits left on the runway have been part of a NASA research project to improve safety and testing methods. Gary Mason reports

runwayThe problem of hazardous take-offs and landings on runways that are wet or subject to snow and ice can be compounded by other contaminates, particularly rubber deposits left by an aircraft’s landing wheels over time.

These deposits need to be removed but aviation authorities give different guidance on when this should happen and the best method for carrying out the task. There are a number of different techniques and technologies available to airports and there are also various types of continuous friction measuring equipment (CFME) that they use to measure the safety of the runway surface for take-offs and landings before and after maintenance work has been carried out.

Thomas J Yager a distinguished research associate from the NASA Research Centre at Langley, Virginia gave a detailed presentation on research work carried out by NASA for the FAA to solve the problem and attempts to standardise procedures.

The research team have recommended that FAA and ICAO come up with a better set of friction testing values that would include grooved runway surfaces. “But when they will be adopted is hard to say,” he told the conference.

ICAO suggested guidelines state that wet runway friction evaluations should be taken when the runways are first constructed and then after routine repair work such as resurfacing, rubber removal and overlays.

Mr Yager told the conference that the time interval between wet runway friction measurements depends on many factors such as aircraft type and frequency of use.

Suggested guidelines from the UK Civil Aviation Authority (CAA) identifies minimum maintenance planning and construction classification values for two CFMEs.

Guidelines from the FAA state that CFME wet friction tests should be regularly performed to monitor each runway third. The guidelines cover eight different types of friction testing equipment taken at two different speeds – 40mph and 60mph. If the friction level measured is below the maintenance planning level in any runway section, corrective action is suggested. But the maintenance planning level varies with each CFME and the speed of the friction measurement run.

The FAA circular provides a suggested friction survey frequency based on average daily aircraft landing runway traffic volumes. So, for example, if there are 15 or less daily landings the tests should be carried out once a year but at the top of the scale if there are more than 200 daily landings the tests need to carried out every week as a minimum requirement.

For removing rubber deposits from runways there are a range of different removal treatments including ultra-high pressure waterblasters, chemical-brush, high velocity shot impact, and mechanical grinding machines.

These again vary on cost, the time it takes to complete the task, environmental impact and any resulting improvement in wet firction performance.

Mr Yager told the conference that the use of mechanical grinders on runway produces a beneficial ‘corduroy’ effect on the landing surface. “As well as removing the rubber deposits this equipment leaves shallow grooves and valleys on the pavement and improve the wet friction performance of the existing surface,” he said.

He added that chemical brushes which are used at airports in the US are more time consuming and costly.

The NASA research made a number of recommendations to improve the impact on safety caused by runway contaminates. These include redesigning air landing gear components particularly the make-up of the landing tyre tread to reduce the amount of rubber deposits left behind.

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