By November 1941, many of the initial assembly-line challenges had been met, which freed up time for the engineering team to tackle the problem of frozen controls in a dive. Lockheed had a few ideas for tests that would help them find an answer. The first solution tried was the fitting of spring-loaded servo tabs on the elevator trailing edge designed to aid the pilot when control yoke forces rose over , as would be expected in a high-speed dive. At that point, the tabs would begin to multiply the effort of the pilot's actions. The expert test pilot, Ralph Virden, was given a specific high-altitude test sequence to follow and was told to restrict his speed and fast maneuvering in denser air at low altitudes, since the new mechanism could exert tremendous leverage under those conditions. A note was taped to the instrument panel of the test craft underscoring this instruction. On 4 November 1941, Virden climbed into YP-38 #1 and completed the test sequence successfully, but 15 minutes later was seen in a steep dive followed by a high-G pullout. The tail unit of the aircraft failed at about during the high-speed dive recovery; Virden was killed in the subsequent crash. The Lockheed design office was justifiably upset, but their design engineers could only conclude that servo tabs were "not" the solution for loss of control in a dive. Lockheed still had to find the problem; the Army Air Forces personnel were sure it was flutter and ordered Lockheed to look more closely at the tail.