The National Transportation Safety Board, citing evidence from the Air Canada fire that killed 23 people, yesterday recommended an immediate inspection of lavatory flushing pump motors on all airplanes to check for electrical damage.

If the Federal Aviation Administration acts on the board's recommendation, the pump motors on all 2,830 planes in the domestic fleet would be subject to inspection, according to FAA officials. The motors are common to many models, not just the McDonnell Douglas DC9 involved in the Air Canada fire, they said.

"We are studying the recommendation, will digest it and have a response later," said FAA spokesman Richard Stafford. The FAA is not required to follow safety board recommendations, but usually does in matters such as this.

Five crew members and 18 passengers on the June 2 Air Canada flight from Dallas to Toronto were able to escape after the plane made an emergency landing at the Greater Cincinnati Airport in suburban Kentucky.

The board's recommendation comes after the Transport Canada Aviation Safety Bureau, which is participating in the investigation, inspected lavatory motors that had previously been removed from DC9s and other planes in Canada.

"An examination of 69 flushing pump motors has disclosed that there was evidence of corrosion in many of the motors and overheat on internal wiring and armature windings of 32 of the motors," the board said in a letter to FAA Administrator J. Lynn Helms.

On July 12, the board said, smoke was observed coming from the rear lavatory of an American International Airways DC9 being serviced at the Charlotte, N.C., airport. The flushing pump motor was examined and showed evidence of having overheated in a manner similar to that reported by the Canadians.

Investigators have not determined whether the pump motor was the source for the Air Canada fire, the board said. It said additional testing is needed to determine if corrosion damage to external wiring or overheating motors is a potential fire hazard.

The board also recommended that the FAA establish regular tests to assure that pump motor wiring has not corroded, and suggested that the FAA tighten requirements for regular removal of trash from lavatory areas to reduce the risk.