For fighter pilots, the difficulty in answering nature's call is as old as flying itself. After all, there are no toilets when you are zooming through the sky at 800 kph.



Over the decades, pilots have used bottles and bags - or just held it. Many avoid liquids, or make sure their last stop before climbing into the cockpit is a bathroom.



|Now a Vermont company has come up with a 21st-century solution that pilots can use without unstrapping themselves from their seats.



The system uses special underwear equipped with a hose linked to a pump the size of a paperback book that drains urine into a collection bag. The men's model uses a pouch; the women's has something that resembles a sanitary napkin.



"As you can imagine, Air Force pilots have many responsibilities during a mission, maintaining their sights, monitoring fuel, navigating the aircraft and monitoring their weapons systems - and they gotta go so bad they can hardly think," said Mark Harvie, president of the system's maker, Omni Medical Systems, Inc. "This takes care of that problem for them."



Some pilots do permanent damage to their bladders by holding it in for hours at a time, which can cause incontinence and other problems.



"The bladder is a muscle," said Dr Sam Trotter, chair of the Urology Department at Fletcher Allen Health care in Burlington. "If you get this chronic overdistention of the bladder, they can have trouble down the road."



At least twice, F-16s have crashed as their pilots tried to urinate. In 1992, one crashed in Turkey after a belt buckle got wedged between the seat and the control stick, prompting the Air Force to urge pilots not to unbuckle completely.



Fighter pilots can also endanger themselves by avoiding liquids: Even a little bit of dehydration can reduce their ability to withstand heavy G-forces, Harvie said.



The standard equipment for urinating in the air now is the "piddle pack" - a pistol-shaped plastic container filled with chemicals that converts urine into a gelatinous substance to be disposed of later.



"If you're flying during the day in clear weather in the summertime when you're not dressed in seven or eight layers, it's a fairly basic procedure," said Col Phil Murdock, a Vermont Air National Guard pilot with 3,500 hours of flying time.



"At the other extreme, wintertime flying across the North Atlantic when you're wearing multiple thermal layers... (or) at night when you're trying to fly formation with other airplanes in rough weather, then it's darn near an emergency procedure," said Murdock, who flies F-16s.



The push for a better system began in earnest after female pilots started flying fighters in 1993, Harvie said. In 2000, the Pentagon sent out a request for proposals, and Harvie answered.



"I read it over with a couple of my people and we sort of snickered, and said 'Oh, you've got to be kidding, they must have a solution for this, they've been flying airplanes since the early

1900s,"' he said.



But they didn't.



He applied for a research grant and built a prototype. Omni, which started out as a five-person operation, now employs 44 people working out of a building in an industrial park.



The company has delivered the first 300 units to the Air Force and is negotiating to provide the system to the Air National Guard. The Navy has bought a handful for testing, as have air forces from at least two NATO allies in Europe.



Major Samantha Weeks, 32, a pilot with the Air Force's Thunderbirds aerial demonstration team, said female pilots have adapted to the situation just like men. Most women now use a commercially available travel toilet. Weeks said she was comfortable with the current system, but she would welcome something new.



"It's great to have one or two different options out there and figure out what works best for you," Weeks said. "I'm glad to see more viable options for female fighter pilots."



The control units that contain the pumps cost about $US2,000 ($A2,100) each. Over their lifetime, the devices should cost an average of $US35 ($A36.55) a flight, Harvie said.



Harvie said his employees have a sense of humour about what they make, but everyone recognises it's important work. "You lose one $US50 million ($A52.21 million) aircraft and you can pay for this system for every pilot in the world forever," Harvie said.

AP