Aircraft

US forest-products company Weyerhaeuser is completing development of a Boeing-conceived firefighting system that can turn any rear-ramp cargo aircraft into a waterbomber.

Final tests of the precision container air delivery system (PCADS) are planned for late August at the US Army's Yuma Proving Grounds in Arizona.

PCADS uses a cardboard box enclosing a biodegradable bladder containing 900kg (2,000lb) of water or retardant. Mounted on plywood pallets, the boxes can be loaded on to an unmodified cargo aircraft like a Lockheed C-130.

The aircraft is then flown at 500ft (150m) and 130kt (240km/h) to GPS co-ordinates within the drop zone, when the pallets are rolled off the rear ramp.

On exiting the aircraft, the box lid acts like a parachute and its straps rip open the bladder, releasing its contents at about 200ft to soak the ground.

Flight tests were conducted in Kingman, Arizona in July, using a Fairchild C-123 cargo aircraft to drop 10 containers over a dry lakebed. The Yuma tests are for military qualification, clearing PCADS for use in Air National Guard aircraft.

Weyerhaeuser says PCADS avoids the hazardous low-level manoeuvres during which several air tankers have crashed, allowing water to be dropped from level flight at higher altitude, even at night and in smoke.

Military qualification is needed to sell the system to the firefighting agencies responsible for hiring commercial operators or calling in the military to fight wildfires.

Interested both in protecting its own forests and selling the cardboard boxes, Weyerhaeuser says the container has to be strong enough to withstand the forces of a rejected take-off, yet be biodegradable.

The box is made of triple-thickness corrugated cardboard, while the bladder - made by Flexible Alternatives - is thin PVC and should decompose within nine months if not recovered by firefighters.

The water bag, 1.2m (48in) in diameter and 1.2m in height, can be filled in 3-5min from a fire hydrant or fire truck, says Weyerhaeuser.

While a C-130 could carry 16 containers, a Boeing C-17 could carry 32 for a total of more than 43.5t of water. The company is also working on a larger container holding almost 7,600kg.