Well Goomed Runways Guide Pilots to Safe Landings

The striped effect of a well mown runway has benefits beyond creating a visually attractive look. It can also be used to encourage pilots to vary their landing lines which leads to a reduction in wear in the centre of a runway.

Pilot Trish Stephens of New Zealand's Tauranga Aero Club says "the runways at Tauranga are pretty good, the view on approach to the grass runways looks like a well mown cricket pitch. The mowing strips are easy to see as you plan your final approach."

Another key element in effective mowing of runways is using techniques and equipment that reduces uneven surfaces which can compromise the safety of landing aircraft.

Stephens who is an accomplished competition flier with 800 hours piloting light aircraft has landed on airfields around New Zealand and is aware of the dangerous wheel ruts caused by tractors and other aircraft.

On traditional mowers that are attached to tractors using a three point linkage, the weight of the mower is mostly borne by the tractor's large rear wheels. This means when the mower is being operated or lifted the weight transfer through the wheel can leave wheel ruts which then can cause problems for landing aircraft.

An alternative is to use a trailed mower with full width rollers front and rear (towed by the Tractor draw bar), which distributes the weight more evenly across a larger surface area and makes turning easier and therefore does not create ruts.

Wider mowers, and those with front and rear rollers on each mowing deck, tend to be more effective for airports than caster wheeled mowers as these can cause ruts in the wet areas.

These are lessons learnt at New Zealand's fifth busiest airport Tauranga. Of the 225 hectares of land owned by the airport, 20 percent is in grass which has to be mown every week to 10 days. The three grass runways at Tauranga cover 11.6 hectares which is used primarily by light aircraft and gliders.

Tauranga Airport manager Ray Dumble says the airport company is now using a Trimax Pegasus S2 five metre trailed roller mower with three mowing decks.

He says the problem of wheel ruts has been eliminated and the extra width means mowing is faster and it costs less to do.

"The mower is saving us 15 to 20 hours a week or half a labour unit, which is a huge saving for the airport.

"It used to take three and a half hours to mow one of our three runways; now it only takes one and a half hours with the Pegasus five metre mower."

Dumble says another benefit is the existing 55 horsepower tractor didn't need upgrading to cope with the bigger mower, which was also a saving.

Trimax Mowing Systems design engineer Jim McEwen says a lot of research has gone into the needs of airports.

He says the technology used in the Pegasus S2 being used at Tauranga was originally developed for the turf industry in the United States and for municipal parks and reserves. But now it is being adapted for airport use around the world.

"We found at airports it was important to be able to move around the sites easily without causing damage.

He says moving the machine is made easy with an hydraulic lift function controlled from the cab which makes for easy transportation on its own suspended transport wheels which also allows for high speed road travel if required.

The driver remains in the cab as the mower unfolds hydraulically, releasing the three multi-spindled roller mower decks. Each deck floats independently of the others and has tri-axis articulation for contour following.

He says full width rollers on all decks produce a striping affect which was shown to be important for airports.

The Pegasus is suited to the vast open spaces on airfields. The mower can cover large areas quickly leaving in its trail a smooth finish required for the safe take-off and landing of light aircraft. McEwen says while Tauranga has a five metre model other options include a larger six metre mower.

Storage is made easy with each of the three mowing platforms lifted in the upright position meaning the mower can be safely parked in the hangar out of harms way.