Qantas has stood down two pilots who had a heated argument in the cockpit of a Boeing 747 jumbo on the tarmac at Dallas's international airport.

Just weeks after Qantas stood down a captain for returning a positive alcohol reading, it has emerged that another captain and a second officer on a 747-400 had an argument over the take-off calculations they should be punching into the passenger jet's computer system.

Qantas has since launched an investigation into the dispute between the two pilots who have been told they cannot fly. The incident occurred last Tuesday night (US time) as a major thunderstorm was rolling across Dallas, causing severe congestion at the city's international airport.

It is rare for pilots to be stood down from operational duties.

Because the pilots were already close to exceeding their 20-hour duty limits due to delays caused by the thunderstorms, Qantas's flight operations managers decided to keep the plane on the ground overnight at Dallas-Fort Worth International Airport.

The managers were later informed of the argument between the pilots and stood them down. It meant the airline had to bring in replacement pilots to fly QF8 back to Sydney via Brisbane the next day.

The jumbo, which can carry about 320 passengers on the ultra long-haul route across the Pacific, had been due to arrive in Brisbane at 5am on Thursday but did not touch down until 18 hours later.

A Qantas spokesman confirmed yesterday that a captain and a second officer had been withheld from service while an investigation was under way.

But he said the flight was late arriving in Brisbane because of the delays caused by the thunderstorms, not the altercation between the two pilots.

"Qantas flight QF8 from Dallas-Fort Worth to Brisbane on 14 August was delayed overnight as a result of severe thunderstorms in the Dallas area,'' he said.

The incident comes three weeks after a Qantas captain was removed from operational duties for testing positive to alcohol. The airline still has an investigation under way into the conduct of that captain, who flight attendants had suspected had been drinking before a flight.

Qantas has been flying to Dallas since May last year when it dropped services to San Francisco in favour of the Texan city, which is a hub for its alliance partner American Airlines. The 747-400 jumbo used on the route is configured to seat 356 passengers but can carry only about 320 people because the ultra-long distance requires a lighter load.

The 13,816-kilometre route is at the upper limit of the jumbo's flying range. Australia-Dallas is one of the longest non-stop routes in the world and the longest flown by 747 jumbos.

- Sydney Morning Herald