Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Executed Go Around / Missed Approach; Flight Crew FLC Overrode Automation
Aircraft
Our departure was delayed due to maintenance checks of autopilot/autoland system. Maintenance advised us that system checked out okay after resetting the main aircraft buses and that previous failure was due to possible sticky relay(s). On approach at glideslope capture and triple channel isolation; the autopilot failed; autothrottle failed; auto brakes kicked off. Captain side displays stopped working; multiple messages on upper EICAS (these items eventually resolved when electrical system reverted to normal configuration). We discontinued the approach. Reset the flight directors. Status messages remaining after system was reset were: MAIN BAT CHRGR; EQPT SMOKE TEST; STBY INVERTER. We were vectored around for a second approach. This approach was hand flown using flight director with no issues.
B757 Captain reported an issue with the autopilot in a coupled approach. A missed approach was necessary followed by a hand flown successful approach and landing.