B737-700
Flight Crew Last 90 Days 188
Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Deviation - Speed All Types; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Regained Aircraft Control; General Maintenance Action
Aircraft
We were at 4;000 FT and given a climb to 6;000 FT. Autopilot 'B' was in use. During the climb at about 5;200 FT; autopilot went into Altitude Capture. At about 5;500 FT to 5;600 FT; the aircraft pitched up to about 20 degrees. The VVI went from 1;200 to almost 5;000 fpm. The autothrottles did not move and the airspeed dropped from 250 to 210 knots. I disconnected the autopilot and pushed the throttles up in an attempt to regain control of the aircraft. We leveled off at about 6;300 FT. The mode control for pitch was Level Change and speed was 250 knots when it happened. A few things that were also strange during this were that the Captain was trying to delete the reduced climb and some of the keys on his FMC would not work. (Mainly the delete key.) We also had a TCAS failure at the same time. Once the aircraft was level at 6;000 FT; we tried to reengage the autopilot in 'B' mode but were unable. We tried both CMD and CWS. Neither would engage. We engaged autopilot 'A' mode and flew the airplane to destination without further problems. Once there; we called Maintenance and they MEL'd both the 'B' autopilot and the TCAS. Once we arrived in base; we asked for Maintenance to come out and we explained everything that had happened. They had several personal there to troubleshoot the problems. We were both at a loss as to why the autopilot would pitch like this when it went into Altitude Capture.
We had been level at 4;000 feet MSL at 210 KIAS accelerating to 250 KIAS and ATC cleared us to climb to 6;000 feet. The First Officer asked for level change; 250 KIAS and then selected autopilot 'B'. We had received a TCAS failure and I was checking circuit breakers. We were climbing at about 2;000 fpm and got ALT ACQUIRE at about 5;300 to 5;400 feet MSL. It appeared the aircraft started to level off.I retested the TCAS system and the First Officer asked to delete CLB-2 reduced power. At about 5;600 to 5;700 feet; the aircraft pitched to about 20 degrees nose up and the autothrottles didn't move. Very quickly; at about 5;800 feet; the First Officer disengaged the autopilot and recovered the aircraft back to level flight at 6;000 feet. We had gotten as high as 6;300 to 6;400 feet MSL. ATC queried our Mode C as they had lost our altitude reporting; I think because of the TCAS test.We verified our altitude at 6;000 feet and they reported our transponder was back online. We reported the TCAS failure to them. After recovery; the aircraft autopilot would not engage in the 'B' channel; but worked normally in 'A'.
B737-700 flight crew reports a vigorous autopilot pitch up as the aircraft is capturing the assigned altitude of 6;000 FT. The autopilot is quickly disconnected by the FP and the aircraft returned to 6;000 FT. Shortly before and during this event the Captain was testing the TCAS and deleting CLB-2 from the autothrust system.