Both electrical generators failed on a Northwest Airlines DC-9, forcing it to land at a small airport, an investigator said. The darkened jet skidded about 1,000 feet off the runway and into a muddy field.

None of the 104 people aboard was seriously hurt in the emergency landing at unattended Monte Vista Municipal Airport in the mountains of southern Colorado early Wednesday.The cabin filled with smoke after the landing, and a crew member had to use an ax to hack open a window and relieve cabin pressure so the doors could open, Northwest spokesman Kevin Whalen said.

The pilot suffered minor cuts and bruises and one of the 99 passengers was treated at a hospital for shock and minor injuries, officials said. Flight 109 had been flying from Minneapolis to Phoenix.

After landing, the pilot used a pay telephone to summon help.

The jet's left generator apparently failed in flight late Tuesday and the pilot tried unsuccessfully to start the auxiliary power unit, said Bob Johnson, the National Transportation Safety Board's regional director in Denver.

The right generator failed soon afterward, Johnson said, and the plane was left with battery backup power, which would have lasted only 25 minutes.

Passengers said there was no panic, even though the captain could not talk with them over the intercom.

"We didn't have any warnings," said passenger Tina Borgmann, 24, of Waseca, Minn. "All we were told is fasten our seatbelts and put our trays in an upright position."

"I just kept thinking, `What's next? Is this thing going to catch fire?"' said Arlene Sevilla of Milwaukee, who held her month-old daughter.

"Then we hit the ground and I just hugged my daughter closer and thought, `Here we go.' "

Passenger Todd Curtis, 28, of Thatcher, Ariz., said: "When the tires blew, the rims just sort of dug into the pavement and slowed us down. I was afraid that we were going to start cartwheeling, but the runway was apparently soft enough that the wheels just dug in."

The runway at Monte Vista is 6,000 feet long, Johnson said. "Under ideal conditions that would be acceptable, but in an emergency situation, it's marginal," the investigator said.

After the crew managed to open the door, the pilot found a pay telephone to summon help.

"There we were in the middle of a field," Sciola said. "We wandered around these buildings and there was a pay phone. The pilot called and said, `Excuse me, we've landed out here in this field and we're going to need some emergency vehicles.' "

Northwest spokesman Bob Gibbons would not release the pilot's name, saying company policy prohibits releasing crew names unless there is a fatality.

Aside from the broken cabin window, the only apparent damage to the plane was flat tires, said Johnson.