A B757-200 flight crew encountered multiple FMC and autoflight system anomalies during initial climb. Among other things an altitude deviation occurred when the aircraft failed to level at the altitude in the altitude select window.
Synopsis
A B757-200 flight crew encountered multiple FMC and autoflight system anomalies during initial climb. Among other things an altitude deviation occurred when the aircraft failed to level at the altitude in the altitude select window.
Narrative
During climb to 5;000 FT and heading 090 degrees we selected VNAV; flaps 5 climb power at 1;500 AGL. The autoflight system then malfunctioned with VNAV switching to climb mode then to continuous with a momentary indication of throttle hold. We then selected the right autopilot and reselected VNAV. Once again the system switched to climb mode then to continuous mode. We checked in with Departure Control and complied with a requested new heading of 170 degrees. With clearance to 5;000 FT whereupon the autopilot failed to capture set altitude. At 5;700; we interceded manually; disconnected the autopilot and auto throttles and descended back to 5;000 FT. ATC cleared us to climb to 16;000 FT. We selected FLCH and initiated a climb. When level at 16;000 FT the aircraft accelerated towards VNE with Flight Director Command Bars directing a descent with 5 degrees nose down. We then deselected both Flight Directors. After approximately 15 minutes; systems stabilized. There were no further erroneous indications or autoflight malfunctions.
Second reporter narrative
The First Officer was flying; I was monitoring...all problems appeared to be with the Air Data system and FMC.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.