FORT CAMPBELL, Ky. (AP) _ An Army exercise in rescuing injured soldiers turned real when two helicopters carrying soldiers ready to descend down ropes collided, sending both aircraft plummeting to the ground. Six soldiers were killed and 28 were injured.

The spinning wreckage fell about 100 feet, just missing the area where the fake accident had been staged and soldiers pretended to be injured. A third helicopter taking part in the exercise managed to fly off safely.

It was the military's second fatal helicopter collision in just over a month, and the second at Fort Campbell this year.

Maj. Joe Howell, a post spokesman who witnessed the crash, said a videotape of Tuesday's accident taken by a spectator showed that the helicopters were flying side by side when one suddenly veered into the other.

The main rotor blades of the two UH-60 Blackhawk helicopters then hit each other. ``It was not a case of them hovering too close,'' Howell said.

One of the pilots survived and was interviewed by investigators, Howell said. The videotape was turned over to investigators.

Nine of the injured were in critical condition, Howell said.

The dead and injured soldiers were from the elite 101st Airborne Division based at Fort Campbell, which straddles the Kentucky-Tennessee line.

Howell said the unit had performed the same drill without any problems earlier this week.

The UH-60 choppers, used for attack missions or medical evacuations, can carry a crew of three or four and about 11 passengers. The Army did not know if any of the soldiers who had been portraying injured troops on the ground were among the dead or injured.

A group of about 22 area business people and officials were watching the mock medical evacuation from bleachers about 100 yards away. Soldiers were to descend from the helicopters by rope to a plywood mockup of a downed helicopter to treat soldiers pretending to be injured, and then airlift them away.

Two civilians, Peggy Poole and Mark Clare, both from Clarksville, Tenn., suffered minor injuries when they were hit by flying debris. Both were treated at the fort's hospital and released.

``There were people running everywhere,'' Poole said. ``It was such chaos out there.''

Said Clare: ``It all happened so quick. You could blink your eye. That's how fast it was.''

Howell said the day was sunny and there was little wind. The exercise area is surrounded by trees, but Howell said the helicopters did not have to maneuver around them.

In March, five soldiers from the fort were killed when an MH-47E Chinook helicopter crashed during a training mission.

An Army report released Tuesday blamed pilot error, saying the pilot may have become ``disoriented during the turn and inadvertently placed the aircraft into an unusual attitude that neither he nor the (instructor pilot) could recover from.''

On May 10, two Marine helicopters taking part in war games involving thousands of British and American troops collided at Camp Lejeune, N.C. Fourteen servicemen were killed and two were seriously injured.