Cleared for landing

After 13 nights resurfacing Palmerston North Airport’s ageing runway, it was cleared for aircraft landings. RICHARD SILCOCK takes a look at this award-winning project.

A Wirtgen milling machine removing the old asphalt.

WHAT COULD HAVE been seen to be a straightforward pavement resurfacing project, was in fact a project that required the upmost care, dedication, adherence to strict aviation safety and security protocols, and the need to meet the stringent skid resistance and quality thresholds for commercial airport runways.

To complicate the project further, all physical work had to be done without impacting on scheduled aircraft operations. This necessitated the work being carried out in three stages over a three-year period at night over weather-favourable weekends.

Higgins acquired the project in conjunction with Beca Airports as consultants with stage one commencing in January 2014 with the third and final stage completed last year.

“While the runway had been ‘rejuvenated’ in places several times since it was originally constructed 34 years ago, it had exceeded its intended design life and was in need of a complete resurface,” says Bruce Walker, the project supervisor with Higgins.

The contract called for the cold milling of a 30mm thick asphalt surface layer along the 1800-metre runway, applying a waterproofing seal and then laying durable new asphalt to a depth of 30mm over an area of 68,000 square metres.

An Air New Zealand ATR aircraft taxies onto the new runway.

To achieve this requirement Higgins used a high strength, open graded porous type of asphalt which was modified with polymer additives and cellulose fibres to provide durability and accommodate the stresses brought about by the all-up weight of aircraft, undercarriage wheels hitting the surface at high speed when landing and the lateral stresses on the pavement when aircraft turn to taxi.

The membrane chip seal applied to the milled surface as a waterproofing and adhesion layer was a heavily modified polymer emulsion.

“Each section of the runway we were working on had to be milled and then reinstated with the new seal and asphalt within a strict timeframe each night, so that aircraft could safely use it during the day,” says Bruce. “To allow for aircraft take-offs and landings we had to schedule work to start following the last flight each night and we had to be finished and safely out of the way by 5.30am the following morning.

“This timeframe not only covered the physical work but also the two hours spent moving the machinery onto and off the runway site and the stringent sweeping and visual safety checks prior to the runway becoming operational again.”

To comply with aviation safety and security regulations all construction staff and ‘visitors’ entering and exiting the site had to go through a security controlled gate, undergo a safety induction procedure and sign a hazard register for each shift.

“Prior to starting work each night a full safety briefing was held for all construction staff, consultants and visitors,” says Bruce. “This was deemed essential due to the number of people on site, the amount of machinery required to maintain the schedule, the multiple operations that were happening simultaneously and the fact the work was happening at night.

“In addition and at the end of each shift, a very detailed and close visual inspection was carried out along the runway to ensure there were no ‘foreign objects’ or any debris left on the runway, as a single stone or loose piece of metal has the potential to cause severe damage to an aircraft’s engines if sucked in, or to the fuselage if flicked up.

“To accomplish this to the required international aviation standard, we would first sweep the runway and then 25 staff in a line-abreast formation would slowly walk the length of the runway visually inspecting it.”

Higgins had around 50 staff on site each night together with up to 34 vehicles and machines. These included two Wirtgen cold planer mills and two Vogele asphalt paving machines fitted with infra-red heaters to bond the milled asphalt with the new asphalt at temperatures in excess of 125 degrees Celsius. Other equipment included rollers, bobcats, water-carts, sweepers, trucks, and utes.

“The possibility of machinery mechanical breakdowns was alleviated by the duplication of all the machinery so that in the event of a breakdown we had a backup machine on standby,” says Bruce. “As it happened we only had one breakdown throughout the entire project, when a milling machine burst a hydraulic hose. We brought in the standby mill to maintain the schedule.

“Following our detailed inspections during the milling stages of the project the ground conditions were as we expected and where there were any anomalies such as variations in the underlying asphalt, we were able to deal with these without impacting on the schedule. Fortunately the weather was on our side over the planned 13 nights, so we were able to meet the target schedule, with no variations and without any incidents.”

All the quality assurance and testing requirements were achieved and subsequent skid resistance and ride quality tests have shown the runway pavement to be well within the required international aviation limits.

The completed runway has an expected life of around 10 to 15 years before any further modifications or upgrades may be required. This will depend on aircraft usage, the weather and other phenomena such as earthquakes.

The project won the Supreme Award for Construction Projects at the Central Districts CCNZ Regional Awards last year, with the judges saying: “The project demonstrated a very high level of organisation, coordination and quality that exceeded client expectations.”

“This award was the icing on the cake for our team in that it recognised the runway resurfacing exceeded the stringent aviation requirements set by the airport authority and international aviation regulations governing airport operations and safety,” says Bruce. “Furthermore the project was delivered within the $2.6 million budget in an extremely tight and limited timeframe without interruption to scheduled aircraft movements.

“Our client was happy, we were happy and we celebrated with a BBQ to top it off.” 

This article first appeared in Contractor September 2017.

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