Heavy Transport
Flight Crew Air Transport Pilot (ATP)
Distraction; Confusion; Training / Qualification; Workload
Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Unstabilized Approach
Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action
Human Factors; Procedure
During approach runway 25L HKG; day VMC; FO (First Officer) was the flying pilot; at about 300 ft he announced: autopilot off auto throttles off; he disconnected the autothrottles with one click which triggered the beeper and master caution; I immediately reset the master caution to silence the beeper; next; the aircraft was pitching up and climbing and the thrust increasing followed by the master warning and siren due to the auto pilot disconnecting; seeing that we were no longer on a stable approach and not in a position to land safely; I called 'go around'; and the go around was initiated; ATC was advised and the autopilot re-engaged; we carried on the missed approach as published. ATC queried about the reason for the Go around and we informed them that it was due to an unstable approach on short final.  During the go around; when the autopilot was re-engaged; I mistakenly selected the left autopilot; now level at 6000 ft on a long downwind portion of the missed approach; still trying to figure out what exactly happened that caused the go around; I asked the FO to disconnect the autopilot so I can engage the right autopilot; and I noticed that he was pushing the TOGA (Take Off Go Around) switches to disconnect the autopilot! It became apparent what happened at 300 ft; he disconnected the autothrottles but mistook the yoke autopilot disconnect switch with the TOGA switches and he pushed the TOGA switches instead; which advanced the thrust levers and initiated an autopilot coupled go around; not realizing why the airplane was pitching up; he overpowered the autopilot by applying forward pressure on the yoke to stop it from pitching up thus disengaging the autopilot and causing the master warning and the siren to go off! After a brief discussion going over what went wrong to avoid repeating the same scenario; ATC vectored us for another approach and the FO flew a stable approach; disconnected the autopilot and autothrottles properly and we landed safely on Runway 25L.
An air carrier Captain reported the First Officer mistakenly pushed the TOGA button on short final while attempting to disconnect the autopilot. A go around was required because of the resultant unstablized approach.