American airline pilots are being allowed to carry handguns on domestic flights from this weekend.
The measure - which is being introduced in the wake of the 11 September 2001 attacks on the US - aims to protect crews and passengers from hijack attempts.
A group of 46 pilots have been attending a two-day course on using firearms at a federal training centre in Glynco, Georgia.
"If one of them is scheduled to fly on Sunday, then as early as Sunday we might have a pilot with a gun in a cockpit," said Transportation Security Administration spokeswoman Heather Rosenker.
The training includes target shooting, defensive tactics and the law regarding the use of force.
There are also psychological tests which indicate whether or not a pilot would have problems about killing another person.
"We want to make sure that everybody that comes to this programme is actually going to able to carry out the duties of the position and use force if it becomes necessary," another TSA spokesman, John Moran, said.
The pilots who qualify will be allowed to carry semi-automatic pistols on domestic US flights served by American carriers.
Congress decided to allow pilots to carry firearms after the 2001 attacks on New York and Washington, despite initial resistance from both the White House and airline companies.
Pilots' representatives argue the measure is essential to provide security in the skies.
One airline captain involved in the training initiative said he thought that as many as a third of US pilots - about 30,000 - could be carrying weapons on the flight deck in five years.
"There has to be something between that cockpit door and that F-16 that's going to blow you out of the sky if the terrorists take over," said Stephen Luckey, chairman of the national security
committee of the Air Line Pilots' Association.
Once they have finished the training course, the pilots take an oath as federal
flight deck officers and are then given the handgun and ammunition
in a metal lockbox.
The weapon is to be withdrawn from the metal box only once the
pilots are installed in the cockpit.
The next group of pilots will be trained in July.