In that case, investigators discovered that one of the plane's airspeed indicators had malfunctioned and that the pilots, who failed to switch to one of the other indicators, had thought they were flying too fast. In response to the erroneous reading, they slowed down until the plane fell out of the sky. The investigators suspected that a pressure sensor was blocked, although not the same one as in the Aeroperu case. In the Dominican crash, the blockage may have been caused by an insect nest, the investigators said.

The National Transportation Safety Board said the McDonnell Douglas Corporation and Airbus Industrie ''have designed protective covers for operators to place over static ports while cleaning and polishing the airplane.'' It added, ''These covers are brightly colored and have warning flags attached to insure that they are seen and removed before flight.''

A spokeswoman for Boeing, Cheryl A. Addams, said the company was planning to manufacture brightly colored covers for the pressure sensors, which are about one inch in diameter. Ms. Addams said the sensors had small holes, ''like a miniature shower drain,'' in the center, in an area about three-eighths of an inch across.

The safety board made its recommendation to the Federal Aviation Administration. An F.A.A. spokesman, Eliot Brenner, said, ''We will study the recommendation thoroughly and respond quickly.''

Just before the crash in Peru, on Oct. 2, the pilot radioed to air traffic controllers that his instruments had gone haywire and that he did not know where he was, Peruvian officials said at the time. The information released today by the National Transportation Safety Board would not explain a failure of navigation equipment but would account for confusion about two vital factors, airspeed and altitude.