By COLLEEN SLEVIN United Airlines plans to start training its pilots to use stun guns to defend their cockpits even though the devices haven't been approved by the Federal Aviation Administration. The nation's second-biggest airline will hold one-day training session for its pilots in Denver and other hub cities such as Chicago and San Francisco starting in April, company spokesman Joe Hopkins said Wednesday. Flight attendants will also be trained in self-defense and helping passengers in the event of a terrorist attack but will not be trained to use the advanced Taser stun guns, which will be kept in locked boxes in the cockpit, he said. The airline, which lost two planes in Sept. 11's terrorist attacks, was the first major U.S. carrier to announce plans to use stun guns on its planes. If the government approves their use, as United is confident it will, Hopkins expects stun guns will be available on its planes by the end of the summer. It will be up to Transportation Secretary Norman Minetta to decide whether stun guns will be allowed on planes. But first staffers at the FAA and the newly formed Transportation Security Administration must review about 10,000 comments from the public about whether to put firearms and less-than-lethal weapons on board, FAA spokesman Alan Kennitcer said. The 1,300 advanced Taser weapons purchased by United for about $1 million will be able to fire two electrical charges that disable attackers for about five seconds, allowing them to be handcuffed or subdued, Hopkins said. Capt. Herb Hunter, spokesman for the Air Line Pilots Association, said installing stun guns is a good step to improve flight security but worries about how effective they would be against someone who is wearing thick clothing or if more than one person breaks into the cockpit. The United Boeing 777 pilot said he still hopes the FAA will allow some pilots to carry handguns.