By Alan Baldwin

LONDON (Reuters) - Pegasus, the winged white stallion of Ancient Greek mythology, may have been the equine world's first frequent flyer but today's Olympic horses are the real globetrotters racking up the air miles.

The biggest and heaviest competitors in the Games are heading for Rio on charter flights from Europe and North America that can take 40 horses at a time. Most have done such journeys many times before.

"These horses are so used to it," New Zealand's British-based double individual eventing gold medalist Mark Todd, preparing for his seventh Olympics at the age of 60, told Reuters. "They do it so often.

"Apart from the takeoff and landing, when they are in the air they get a smoother ride than driving down the road where there's all the twists and turns and accelerating and slowing down.

"For them it's probably an easier trip."

Vets and grooms travel with them, keeping feed and water levels topped up, and each horse has a 'baggage allowance' of 300kg of kit.

The first eventing charter leaves London's Stansted airport on Friday for an 11 hour and 40 minute flight to the first Olympics in South America. Others depart over the weekend from Liege in Belgium and Miami.

Dressage and showjumping horses have separate flights.

Flying from Stansted will be British-stabled horses from teams including New Zealand, Australia and China and all will have undergone a 14-day period under vet supervision in sterile yarding.

"We basically get all the horses to one yard, to Mark Todd's yard, and they get picked up by the official carrier Peden," New Zealand equestrian's high performance director Sarah Dalziell-Clout told Reuters.

"(On the flight) they are in a box that contains them so it's not like they can move around. They are stationary and there's a bar in front and a bar behind."

Shipping agents Peden Bloodstock have flown horses to the Olympics since Montreal in 1976. For the 2008 Beijing Games, that meant flying 287 horses into Hong Kong on 57 aircraft from around the world.

On arrival in Brazil the horses, who sleep standing up, will travel under police escort along a "bio-contained" route to the Olympic venue at Diadoro.

The trickier part has been negotiating local regulations and bureaucracy which mean teams must list everything imported, down to the hoof picks.

"The Brazilian authorities have been really strict on what can be brought into the country," said Dalziell-Clout.

"It does strike some of us as a little bit strange... because they've certainly got conditions over there like Glanders (a potentially fatal horse disease) that other regions don't have. But they are taking a very strict control on it."

(Additional reporting by Caroline Stauffer in Rio de Janeiro, editing by Sudipto Ganguly)