WASHINGTON -- In their first suggestion that a mechanical flaw might have caused a fatal jetliner crash in Colorado five months ago, accident investigators recommended yesterday inspections of the rudder controls on Boeing 737 and 727 jets.
Although the investigators, from the National Transportation Safety Board, said they still had not figured out why the 737 crashed in Colorado, they said they had detected a problem that could cause the rudder to move on its own, making the plane difficult to control.
The safety board also said that Boeing detected the same problem on three 737 planes in the mid-1980s and made a design change in 1986.
But the board said that the change was never installed on planes that were already in service, including the plane involved in the accident this year. Nor were inspections of existing planes ever ordered.
The safety board, an independent federal agency that investigates transportation accidents, has no authority to require inspections of airplanes. Its disclosures and recommendations yesterday came in a letter to the Federal Aviation Administration, which has the authority to order the inspections.
A spokesman for the FAA said it had just received the safety board's letter and was studying it. He called the issue a top priority for the FAA.
Steven P. Smith, a Boeing spokesman, said the company had just received the safety board's report and was studying it. "As always, we take the NTSB's recommendations seriously," he said.
The Boeing 737 is the world's most widely used passenger jet, with more than 1,900 planes in operation. The 727, which uses a similar rudder control, is the second most widely used model, with more than 1,700 in service.
But Boeing and federal officials said they were not sure how many planes would be covered by the board's recommendations. Until now there has been no explanation why the United Airlines 737 suddenly flipped over while trying to land at Colorado Springs in March, diving nose first into the ground, killing all 25 people on board.
Investigators have been examining gusty winds as a possible cause, but they were also troubled by records showing that the 737 that crashed had experienced rudder problems twice in the weeks before the crash.