Ill-fated Continental Flight 1713 waited so long before takeoff at Denver airport after a de-icing that its wings accumulated enough new ice to hinder the jet's ability to fly, federal investigators say.

The findings of the National Transportation Safety Board, released Tuesday, said the McDonnell Douglas DC-9 had been so thoroughly de-iced that some of the de-icing fluid seeped into the cabin.But because of poor visibility and, in part, confused radio communications, the jetliner had to wait 27 minutes in a steady snowfall before taking off for Boise, Idaho.

It was airborne only a few seconds before crashing onto the runway, killing 28 of the 82 people aboard.

The NTSB report also said Lee Bruecher, the 26-year-old copilot who was at the controls during takeoff, rotated the plane off the runway too sharply, causing its nose to veer up at a high angle and adding to its problems staying aloft.

Among the dead were Bruecher and Capt. Frank Zvonek, 46, who had failed to order the jet back to the de-icing pad contrary to airline operating procedures, the safety board said in its final report on the Nov. 15, 1987 accident.

The board's findings were challenged by Continental Airlines, which said the investigation had not shown specifically that ice had accumulated on the wings of Flight 1713.

The nearly yearlong investigation focused on the failure to de-ice the aircraft a second time and on the experience and training of Bruecher and Zvonek.

Continental's operations manual required a plane to return to the de-icing pad if it was delayed 20 or more minutes in the conditions experienced in Denver that November day, investigators said.

The failure to de-ice has been the cause of two other major aviation accidents in the past six years: the crash of an Air Florida jet at Washington D.C. in 1982, killing 78 people, and the crash of an Arrow Air charter flight full of U.S. soldiers in Gander, Newfoundland, killing all 256 on board.

The airline has all along maintained that the pilot of the departing Continental jet lost control because of air currents - a phenomenon called a wake vortex - from a Boeing 767 landing three minutes earlier on a parallel runway. But the NTSB report said the theory had been looked at and discounted because of the relative position of the two planes when Flight 1713 began having problems.