Incident Description
While climbing through 26,000 feet, an airplane began to pitch up and down at a fast rate. The captain took control and leveled off, but the oscillations continued. The autopilot was engaged and the airplane stabilized. When the aircraft was slowed to 230 knots and the autopilot was turned off, the pitch oscillations resumed. The crew declared an emergency and returned to Newark International Airport, Newark, New Jersey, where the airplane landed without incident.
Examination Results
The left inboard elevator parallel engage solenoid shut off valve was replaced, and no further discrepancies were noted with the system. Examination of the faulty valve revealed a short between coil 1 and coil 2. Disassembly showed hydraulic fluid underneath the case assembly and around the coil assembly. Additionally, the orange lead to coil 1 and the brown lead to coil 2 had fused together through their insulation, causing the electrical short. Investigators could not determine how hydraulic fluid entered the valve or whether the fluid contributed to the short.
Subsequent Actions
At the time of this report, Boeing was in the process of establishing a components team to research the possibility of fluid contamination in these valves.