B767-300 and 300 ER
Flight Crew Last 90 Days 180; Flight Crew Total 13000; Flight Crew Type 180
Workload; Human-Machine Interface; Situational Awareness; Confusion; Time Pressure; Troubleshooting
Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Aircraft Equipment Problem Dissipated; Flight Crew Executed Go Around / Missed Approach; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action; General Declared Emergency
Aircraft; Weather
I was descending on the arrival. Autopilot and autothrottles were engaged. Aircraft was flying VNAV descent and doing a good job of meeting the initial crossing restrictions. I don't have a chart handy; but I think the incident occurred around the first intersection with a speed and altitude restriction. I initially noticed that the aircraft wasn't slowing in a timely manner to meet the speed restriction; so I deployed the speedbrakes to assist. As the aircraft slowed I ordered the flaps extended to the 1 and 5 positions. When I stowed the speedbrakes I noticed that the aircraft wanted to accelerate again. At this time we were approaching the intersection and the aircraft was approaching the limit altitude. Around this time I noticed the Autopilot Disconnect advisory illuminated temporarily on the EICAS; but there was no aural warning. I also looked at the autopilot engagement button on the MCP and noticed that it was still illuminated; which meant that the autopilot should still be engaged. At this point the aircraft began descending below the minimum altitude at the intersection. I repeatedly pressed the autopilot disconnect button on the yoke and tried to level the aircraft. I also tried to trim the aircraft with no noticeable effect. I looked at the trim indicator and noticed that it was in the normal range. When I attempted to manually fly the aircraft there was an extremely heavy nose down force; and I initially thought the autopilot didn't disconnect. I was having trouble holding enough force on the yoke to level the aircraft; so I asked the Captain to assist me. With both of us pulling; and as power was applied; we were able to level the aircraft. At that point; we declared an emergency; and asked for vectors so we could figure out what we were dealing with. We ran the Jammed Flight Controls Checklist; which didn't seem to help. As we were vectored for the approach the Captain advised that the control forces were returning to normal. This lead us to believe that maybe something involved with the elevator had frozen. Before we departed that evening the aircraft was exposed to several hours of very heavy rain; and also heavy rain on the climb-out. The Captain made a normal landing; and we taxied to the gate without any more issues.
As the First Officer began to slow the airplane down as we set up for the approach; we received and uncommanded EICAS message stating the Autopilot disconnected; however the center autopilot command button on the MCP was still illuminated. There was No pitch control through the yolk and an uncontrolled descent continued. Several attempts to disconnect the autopilot were made; as it felt that only a partial disconnect took place. It wasn't until the Autopilot Bar was switched OFF that the light in the Center Auto button went off; however there was still no pitch control available. We declared an emergency and request that we abort the approach and go-around to complete the Flight Control Jammed or Restricted Checklist. The cabin and Dispatch were briefed. As we descend and flew into warmer conditions; gradually; the pitch response began to return. After flying an extended downwind; I started feeling confident that we could now control the airplane and attempt a normal landing. The landing was uneventful. We believe that the flight control surfaces (elevator) may have iced over; restricting pitch control. We took on a tremendous amount of rain prior to departure.
A B767-300 crew reported an apparent ice frozen elevator system after exposure to heavy precipitation prior to departure followed by a long high altitude flight. The autopilot failed to operate the elevator and two pilots had difficulty leveling the aircraft during descent until the apparent ice melted at lower altitudes.