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After the accident the aircraft was lifted and transported to a hangar where an inspection of the landing gear and its retracting mechanism was conducted. The inspection revealed a failure of a short section of an aluminum alloy tube in the hydraulic down-pressure line. This tube was found ruptured along a length of about 1 inch and, at a number of points, was swollen due to excessive internal pressure. After this failed tube had been replaced, the landing gear retracting mechanism was operated and functioned normally. Subsequently parts of the mechanism were disassembled and it was discovered that the plunger of the right latch was slightly damaged. The damaged latch assembly and the failed hydraulic tube, as well as a similar undamaged tube, were subsequently submitted by the Civil Aeronautics Board to the National Bureau of Standards for examination and tests. The examination indicated that the damage to the plunger had probably occurred prior to the accident. It is not believed that this damage had contributed to the accident. The examination and tests of the hydraulic tubes indicated that the failed tube had not been defective, but that it had burst as a result of an internal pressure considerably higher than that for which it was designed. It appears that this excessive pressure developed as the weight of the airplane was applied to the unlatched landing gear.
On this model aircraft the electrical signal system of the landing gear consists of green and red lights to indicate the down and up positions respectively. These lights are operated by a contact switch located on the landing gear proper rather than on the latch. Inasmuch as the electrical contact is not directly at the latches, it is possible when the landing gear is out of adjustment, for the green signals to light when the landing gear is in a down position even though the latches are not fully engaged. During the testing of the landing gear after the accident, the electrical signal system was also carefully checked, and found to be adjusted and operating properly.
The condition of the landing gear retracting mechanism and the electrical signal system, as found after the accident, indicates quite clearly that the retraction of the gear was caused by an inadvertent release of the latches during the landing roll. Assuming that the latches were operating properly, and there was no reason to believe otherwise, there is only one possible explanation of the release of the latches at that time, viz., the raising of the landing gear handle in the cockpit. The landing gear handle is located on the left side of a centrally placed panel, and there is a similar handle used to actuate the flaps which is located on the right side of the panel in the same relative position. The landing gear handle is equipped with an automatic locking device operated by means of a solenoid which is wired to the torque arm on the landing gear shock strut. The solenoid is energized when the shock absorber is deflected by the weight of the airplane on the gear. The purpose of the locking device is to eliminate an inadvertent movement of the handle while the airplane is on the ground. Such a system cannot be considered dependable because a shock absorber can stick in the extended position and/or a bad electrical contact can occur.
