B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 90; Flight Crew Total 10000; Flight Crew Type 5000
Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Diverted; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
I was returning from my scheduled break when I was asked by the flying pilots to go to the back of the aircraft and observe if the aircraft was doing anything abnormal. I walked back to the aft galley and noticed that the aircraft was oscillating pitch up and down while in smooth air conditions. I returned to the flight deck and observed the right side elevator indicator on the status page oscillating at the same rate that was consistent with what I was feeling in the back of the aircraft. I relieved the Captain from her seat and had her go back to observe the uncommanded pitch movements. Upon her return; we discussed our options with Maintenance Control and Dispatch; and decided that this was a safety of flight concern rendering the aircraft unsafe to continue flight operations. We ran all appropriate checklist items; and diverted to ZZZZ. During the approach; elevator oscillations were noted all the way down the ILS; with the autopilot coupled and also when the aircraft was being manually flown by the crew. After an uneventful and successful landing at the airport; the First Officer and myself did a post flight walk around and noticed that the right side elevator was completely drooped down while the left side was only partially drooped.
Reporter stated they were about two hours into the flight when he went to the aft cabin and noticed the vertical pitch oscillations that felt like an asymmetrical force input; not turbulence induced. Back in the flight deck; all three left; center; right hydraulic system pressures to the elevators were normal. The right elevator chevron on the EICAS Status was definitely oscillating from just above to slightly below the left elevator chevron. The oscillations became more noticeable the slower the aircraft flew. After landing; the right elevator was noticeably drooped; almost vertical. No hydraulic leaks were noted. Reporter stated their air carrier sent a Maintenance team to the diverted B767-300 aircraft. Initially Maintenance thought the problem was an indication error after looking at the aircraft; but he (reporter) again described the inflight oscillations that had occurred. The aircraft was ferried to a maintenance base. He does not know what Maintenance might have repaired; but he suspects an input rod was not properly re-secured during an A-Check that had just been accomplished on the aircraft prior to their departure.
Aircraft had just come out of A-Check and mechanics were still completing Class II navigation checks when we arrived. Climbing out of ZZZ; with center Autopilot (AP) on command; the airplane failed to level off at FL240. Captain caught it and leveled off normally without exceeding 150 feet. AP appeared to behave normally thereafter.We noticed the ALT FLAP CONT circuit breaker (C/B) was popped. We attempted to contact ZZZ Dispatch and Maintenance Control via SATCOM; but could not get through. Sent ACARS messages to Dispatch; but they couldn't call us either. Tried ZZZ State Radio and ZZZZ Radio frequencies off the COMM page from the route section; and also every other frequency shown on the COMM page and none of them worked. Asked ZZZZ domestic for an HF frequency; and managed to establish a HF patch to [ZZZ] Dispatch and Maintenance Control.By this time we had checked the [EICAS] status page and noticed the Elevator Flight Control Indications showed a steady oscillation on the right elevator. We asked the Relief Pilot to check the aft section of the airplane before coming back to the cockpit for crew change. He returned to the cockpit and reported a vibration and pitching movement in the back of the aircraft. He then observed the status page and indicated his observations were consistent with the indications.The left elevator [EICAS] chevron appeared in a normal position. The right elevator chevron was oscillating from a position in which the lower part of the right chevron was above the top part of the left chevron; to a position in which the upper part of the right chevron was below the lower edge of the left chevron. Although it was moving rapidly; it appeared to be oscillating approximately 1.25-1.50 chevron widths.We were approaching ZZZZZ intersection and the entry into ETOPS airspace. Maintenance Control had no suggestions except to try alternate autopilots; which we declined to do; as we believed that it was a greater threat to safety to start troubleshooting an elevator issue. The Captain went back to investigate the situation herself. She found the vibration and rhythmic pitching motion perceptible from the middle of economy class; and distinctly present from approximately row 29-30. There was a definite pitching and oscillation in the back of the airplane which was not present in the front; and it became rapidly apparent. The bouncing was enough to briefly lift the Captain. The airplane was in smooth air.We decided as a crew to divert to a suitable airport and not to enter ETOPS airspace and continue to [destination.]  We had previously just checked weather at airports in the region. ZZZZ was VFR and nearby; and we diverted to ZZZZ.The Relief FO remained on the frequency with ZZZ Dispatch and Maintenance Control; while the Captain and FO flew and coordinated with ATC. We worked together as a crew to minimize stresses on the aircraft; and turned at 15 degrees bank toward ZZZZ; descended from FL350 to FL260 and then FL200 and slowly down to the airport. We reviewed abnormal and normal landing checklists; used the diversion guide and coordinated with ZZZZ authorities. After getting landing data for flaps 25 and flaps 30; we made a flaps 25 landing. During the descent we noticed the elevator oscillations remained at the same frequency; or momentarily reduced. The ailerons indicated asymmetrical position; even though the yoke indicated 0 position. At approximately 6;000 feet and 210 knots; the oscillations were momentarily reduced. At approximately 500 feet; the airplane pitched down at an abnormal rate; and the Captain clicked off the autopilot to fly and land the airplane normally. After landing; the crew conducted a postflight inspection. The left elevator was in a normal faired position. The right elevator was completely down; in an almost vertical position. The cockpit indications on the status page matched the visual observations outside.
A Captain and First Officer describe the pitch oscillations their B767-300 aircraft experienced in smooth air about two hours after departure. The right elevator indicator on the EICAS status page was oscillating at the same rate that was consistent with what was felt in the back of the aircraft. The oscillations were more noticeable as the aircraft slowed and continued all the way to a diverted landing. Aircraft was ferried to a maintenance base.