On July 19, 1993, at 2242 central daylight time (cdt), a British Aerospace 146-300A, N611AW, operated by Air Wisconsin, Incorporated, of Appleton, Wisconsin, as flight number 5140, and piloted by an airline transport certificated crew, experienced a fire on the number four engine during initial climb following takeoff from O'Hare International Airport, Chicago, Illinois. Visual meteorological conditions prevailed at the time of the incident. The 14 CFR Part 121 air carrier flight was operating on an IFR flight plan. The pilots, two flight attendants, and 4 passengers reported no injuries. The flight originated from Chicago, Illinois, at 2239 cdt. The captain said that during initial climb following takeoff a flight attendant observed a glow near the end of number four engine jet pipe. He stated that a fire warning light was not observed in the cockpit when the glow was observed by the flight attendant. The glow was no longer observed when the takeoff power setting was reduced to the climb power setting. He stated the difference between takeoff power and climb power settings is a two percent rollback. The airplane continued to its destination. The jet pipe area is not part of the fire/overheat detection and warning system. The detection and warning system is associated with the engine's fan casing bay and core engine assembly. An examination of the number four engine revealed a crack in the right-hand fuel manifold assembly (manifold) and a small hole burned through the engine fairing reinforcement ribs. Damage, similar to flame damage, was observed on the engine fairing skin next to the jet pipe. The manifold has cutouts (scallops) between its mounting bolt holes. The crack was located next to the number nine fuel nozzle, on the radius of the scallop. The metal thickness between the inner wall of the manifold's fuel channel and scallop surface was .042 inch. Company maintenance records showed the manifold had a total time of 7,581 hours and 11,185 cycles on it. The last inspection on the manifold was conducted 1,742 hours and 2,597 cycles before the failure. The engine manufacturer redesigned the manifold with an approximate .085 inch thickness about one year before this incident. Installation of the revised manifold was optional. According to the engine's manufacturer, the fuel manifold was an older design that had thinner metal near the crack.