Gen. Ralph E. Eberhart, head of U.S. Northern Command, said a strong set of safeguards are in place to prevent an accidental or unwarranted shootdown of a commercial airplane. Commanders, pilots and air defense crews are drilled on those procedures as many as four times each week, Eberhart said.
The rules allow for an order to shoot down a civilian plane only if there is no other option to prevent a Sept. 11-style attack on the ground, the general said. There are authentication procedures for such orders to make sure "someone can't just get on the radio and say, 'This is the president, I order you to shoot down that plane,"' Eberhart said.
Military jets were in the air during the 2001 attacks but were too far away to shoot down the planes before they struck the World Trade Center and Pentagon.
Airline passengers can be confident that their planes will not be accidentally shot down, Eberhart said.
"I would take issue with anyone who would say the men and women in our armed forces are trigger happy," Eberhart said at a breakfast meeting with reporters. "I'm more worried that they would be trigger hesitant than trigger happy. We have long discussions with people to see if they're ready to do this."
Eberhart said he has never heard of a case where a pilot or missile battery operator was hesitant to shoot down a hijacked airliner. Those involved have repeated psychological screening and testing on the procedures to make sure they will follow those rules, Eberhart said.
The Pentagon created Northern Command in the wake of the 2001 terrorist attacks to coordinate military defense of the United States and response to attacks or natural disasters.
Eberhart, a four-star general from the Air Force, said the al Qaeda terrorist network responsible for the attacks two years ago has been seriously damaged.
"Most of the varsity players are gone. In most cases we're dealing with the junior varsity team or the freshman team," Eberhart said.
"But we can't rest on our laurels. We've got to keep the throttle up ... If anything, I think we've bought ourselves some time."
The arrests of three workers at the Guantanamo Bay prison camp for terrorist suspects have illustrated a concern about terrorists trying to penetrate the U.S. military, Eberhart said. The general said he had no indications of any coordinated terrorist effort to recruit American troops but said he had no doubt such efforts were happening.
"There's no doubt that there are people out there trying to turn our people," Eberhart said. "I'm sure there are people right now being worked on as we speak, and it's not working, and they're reporting it."