Narrative:

I returned from break and we were at FL370; assigned mach .82. Briefed the unoko 25N arrival with the transition to the ILS Y 25R. Completed descent checklist and control gave us initial descent to FL350. Clearance complied with autopilot on and VNAV speed. Shortly; thereafter; we were given a descent to FL250 in 50 nautical miles with a transition from mach .82 to 310kts. No specific point on flight plan was given to be at FL250; just a range. I picked a conservative point (fix) within 50nm; engaged VNAV speed with throttle 'hold' annunciated.I briefed one more item during descent regarding transition level at FL070. My first officer (first officer); prior to off the blocks advised me he is a full-time bunky (rfo; relief officer) and doesn't get much time in the right seat. Trying to be a nice guy I stated; 'if you have questions feel free to ask.' he was struggling with communications in maastricht airspace right from the start.things went south after I mentioned the transition level with a response from first officer; 'where did you get that.' I mentioned the ATIS and a few seconds later next question; 'where is it in the box?' now we are fumbling with the box and I was losing my profile in reaching FL250. I check VNAV and we are in a cruise descent with mach .82; no transition speed. I check the descent page and there is 310 kts. I did not insert that speed but I chose to return to cruise descent and manually insert 310 kts. As it appeared we were slowing. The arc on map mode was extending further from the airplane and in hindsight the better option would have been flight level change. More frustration from first officer and I tried to become an instructor at the wrong time. I was flying pilot and should have been flying the jet. Next thing I hear is the overspeed siren and I initially thought autopilot. Fatigue and distraction were factors. We were around FL280; not FL210 per our write up; clean configuration and 12-15 kts. Of overspeed. I disengaged autopilot; raised the nose to decelerate and extended speed brakes. The ordeal lasted 10-12 seconds.not sure what our bunky was observing but I take full responsibility for my degraded situational awareness. Rest of approach & landing was SOP. Debriefed maintenance on the ground with appropriate log book entries.

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Original NASA ASRS Text

Title: B777 Captain reported First Officer unfamiliar with descent procedure.

Narrative: I returned from break and we were at FL370; assigned Mach .82. Briefed the UNOKO 25N arrival with the transition to the ILS Y 25R. Completed Descent checklist and Control gave us initial descent to FL350. Clearance complied with autopilot on and VNAV Speed. Shortly; thereafter; we were given a descent to FL250 in 50 nautical miles with a transition from MACH .82 to 310kts. No specific point on flight plan was given to be at FL250; just a range. I picked a conservative point (fix) within 50nm; engaged VNAV speed with throttle 'HOLD' annunciated.I briefed one more item during descent regarding Transition Level at FL070. My FO (First Officer); prior to off the blocks advised me he is a full-time bunky (RFO; Relief Officer) and doesn't get much time in the right seat. Trying to be a nice guy I stated; 'If you have questions feel free to ask.' He was struggling with communications in Maastricht airspace right from the start.Things went south after I mentioned the Transition Level with a response from FO; 'Where did you get that.' I mentioned the ATIS and a few seconds later next question; 'where is it in the box?' Now we are fumbling with the box and I was losing my profile in reaching FL250. I check VNAV and we are in a cruise descent with MACH .82; no transition speed. I check the descent page and there is 310 kts. I did not insert that speed but I chose to return to cruise descent and manually insert 310 kts. as it appeared we were slowing. The arc on map mode was extending further from the airplane and in hindsight the better option would have been flight level change. More frustration from FO and I tried to become an instructor at the wrong time. I was flying pilot and should have been flying the jet. Next thing I hear is the overspeed siren and I initially thought autopilot. Fatigue and distraction were factors. We were around FL280; not FL210 per our write up; clean configuration and 12-15 kts. of overspeed. I disengaged autopilot; raised the nose to decelerate and extended speed brakes. The ordeal lasted 10-12 seconds.Not sure what our bunky was observing but I take full responsibility for my degraded situational awareness. Rest of approach & landing was SOP. Debriefed maintenance on the ground with appropriate log book entries.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.