Page:CAB Accident Report, Boeing Test Flight Crash on 19 October 1959.pdf/7

- 7 - A flight recorder was installed in the aircraft but was not in operation during this flight. Civil Air Regulations require the flight recorder to be in use during scheduled passenger operations only.

There is little question that the violent gyrations of N 7071 which followed the improper Dutch Roll recovery attempt resulted in the separation of the three engines and the inflight fire. A safety factor is designed into the nacelle supporting structure so that, in the event of abnormal loading, it will fall before destructive loads are transmitted to the aircraft wing. Separation of engines from the aircraft is therefore expected when the aircraft is subjected to high abnormal loadings such as occurred in this case.

It is equally clear that the Dutch Rolls being performed reached angles of bank far in excess of the limitations established by the company. Responsibility for the safety of this aircraft rested solely on the instructor—pilot. The Board can find no valid reason for Mr. Baum initiating the final Dutch Roll so violently. No training advantage could be gained by conducting these maneuvers at the extreme angles of bank reached. Baum certainly should have been aware of this and he was admittedly aware of the company's restrictions. In addition, it was surely less than prudent to permit a pilot with no previous experience in the airplane to attempt a recovery from this extreme maneuver.

The severity of the gyrations to which the aircraft was subjected developed loads greater than the design strength of the nacelle pylon structure. After the three engines were lost and while the flaps were still extended 40 degrees, the airplane was committed to land. The flaps may have been raised to the 28-degree position intentionally so that full outboard aileron effectiveness would be available during the landing. It is possible that in this configuration, with power available from the No. 3 engine, the airplane could have flown at least long enough to reach a suitable airport for a crash landing. However, the intense fire which is believed to have come from a ruptured fuel line, was threatening the left wing and made an immediate landing mandatory.

Lateral control with flaps down at least 28 degrees is provided by the following: Outboard ailerons, 40 percent, outboard spoilers, 30 percent, inboard ailerons, 15 percent, and inboard spoilers, 15 percent. The outboard ailerons are moved by means of a cable bus arrangement actuated by movement of the inboard ailerons. As the fire gradually destroyed the inboard left aileron and the flight control components in that area, the outboard ailerons were lost. Loss of electrical power cut out the auxiliary hydraulic system which operates the inboard spoilers and the rudder boost. When the left inboard aileron was consumed the only lateral control remaining to keep the heavily damaged left wing up came from the right inboard aileron (7-1/2 percent) and possibly the right outboard spoiler (30 percent). Lift on the left wing was seriously impaired because of the loss of approximately 35 square feet of upper surface which was burned through, the additional fire damage to the flaps which reduced their effectiveness, the extra drag from the No. 2 pylon stub, and the spoiler effect on the upper wing surface caused by the ruptured skin over the fuel vent channels.