B.F. Goodrich Co. and Rockwell International Inc., makers of airplane equipment, said they formed a maintenance alliance they hope will help stabilize earnings during an expected slump in aircraft production. Rockwell Collins, which specializes in instrumentation and in-flight entertainment systems, will work with Goodrich Aviation Services to provide one-stop maintenance and repair services to airlines worldwide, the companies said. Goodrich services equipment that includes airframes, landing systems, thrust reversers, evacuation slides and engine components. By providing steady revenue instead of one-time sales, maintenance and parts will stabilize earnings as production of new aircraft declines in 2000, analysts said. Goodrich, based in Charlotte, N.C., is the largest U.S. maker of aircraft landing gear. Its shares fell 50 cents to close at $22.81 on the NYSE.