After only eight F-89As had been built, production shifted to the F-89B (Model N-35). These were the remainder of the May 1949 production order. The F-89B differed from the A only in various items of internal equipment. It carried a Lear F-5 autopilot, an instrument landing system (ILS), and a Sperry Zero-Reader (which combined the features of artificial horizon, directional gyro, magnetic compass, and altimeter). The armament and the radar were unchanged.
The first production F-89B was accepted during February of 1951, and entered service with the 84th Fighter Interceptor Squadron, 78th Fighter Interceptor Group based at Hamilton AFB, California during June of 1951. Three other squadrons received F-89Bs in early l952-the 27th FIS, the 7rth FIS, and the 174th FIS.
After a rash of engine failures on early F-89Bs, the aircraft were reengined with Allison J35-A-21A turbojets, rated at 5100 lb.st.dry and 6800 lb.st with afterburning. These engines had an engine oil scavenging system and different kinds of afterburner eyelids, which gave smoother afterburner control.
All F-89Bs were fitted with external mass-balanced elevators which were adopted to overcome a sever flutter caused by the jet exhaust. However, they were fitted retroactively with elevators having internal mass balance after this feature had been developed for the F-89C.
In retrospect, the F-89B was rushed into squadron service too rapidly. There were not enough trained pilots and radar operators, and there were not enough maintenance personnel who knew the intricacies of the complex and troublesome Hughes E-1 fire control system. The in-service rate of the F-89B was appallingly low, and crashes were all too frequently. On September 22, 1952, the entire F-89 fleet had to be grounded, and the planes remained grounded for 7 months.
The service of the F-89B with the USAF was quite brief. By 1954, all F-89Bs had been transferred to the Air National Guard. The first Guard unit to re-equip with the F-89B was the 176th Fighter Interceptor Squadron of the 128th Fighter Interceptor Wing of the Wisconsin ANG, replacing that unit's piston-engined F-51s.
Several obsolete F-89Bs were later modified as DF-89B radio-controlled drones. One F-89B (49-2463) was modified during assembly as the sole YF-89D service test aircraft.
49-2439/2478 Northrop F-89B Scorpion