With the first prototype's repairs completed, it also joined the flight test program, completing captive flights. While in flight, the Goblin was stable, easy to fly, and recoverable from spins, although initial estimates of a 648 mph (1,043 km/h) top speed proved optimistic. The first test flights revealed that turbulence during approach to the B-29 was significant, leading to the addition of upper and lower fins at the extreme rear fuselage, as well as two wingtip fins to compensate for the increased directional instability in docking. All the initial flights had the hook secured in a fixed position, but when the hook was stowed and later raised, the resulting buffeting added to the difficulty in attempting a hookup. To address the problem, small aerodynamic fairings were added to the hook well that reduced the buffeting when the hook was extended and retracted. When testing resumed, on the 18 March 1949 test flight, Schoch continued to have difficulty in hooking up, striking and damaging the trapeze's nose-stabilizing section, before resorting to another emergency belly landing. After repairs to the trapeze, Schoch flew the first prototype on 8 April 1949, completing a 30-minute free flight test, but after three attempts, abandoned his efforts and resorted to another belly landing at Muroc.