B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Distraction; Workload
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Company Policy; Human Factors
On preflight 40;000 [was] entered in cruise altitude. On climb out [we were] issued FL410; we checked weight and optimal altitude temperature was +17 and we were heavy for FL410; requested FL390 instead. It took a couple of calls to understand ATC's acknowledgement. Somewhere in this process the Flight Attendant called for [warmer] temperature in cabin. Captain answered and told me to adjust temperature. This interruption distracted [us] from entering FL390 in MCP and FMS. Aircraft climbed to 39;800 before we caught it; then center reminded us we were given 39;000 and [to] descend.
I was the pilot not flying as we were climbing through FL250 when Merida Center assigned us FL410 for our final altitude. The pilot flying requested me to ask Merida Center for FL390 as a final altitude since we were too heavy for FL410. I requested and was immediately re-cleared to FL390. I called 'climb and maintain 390' to the pilot flying. He repeated the call out to climb to FL390 and started to wind the altitude control knob up. At this instant the Flight Attendant 'dinged' us on the cabin call channel and I went 'heads down' to answer the call on the audio control panel before verifying that the pilot flying actually rolled 39;000 in the altitude control window. After answering the Flight Attendant's call and request to warm up the cabin; my attention went to the air conditioning panel. Now; after returning my attention back to the status of our climb; all seemed normal. I did not notice that the pilot flying had set 40;000 in the altitude window instead of 39;000 that Merida Center had reassigned. When we passed through FL390 the pilot flying made the call '390 for 400' and I repeated the call. After 20-30 seconds Merida Center asked what altitude we were at and I called out FL400 as we were approximately 39;900. Center then announced to us that we had been assigned FL390 and instructed us to return to FL390. We immediately returned to FL390 in a normal descent. There were no other aircraft visible on TCAS (80 NM range) during this entire time period that I recall. The rest of the flight was uneventful (other than the discussion of how exactly the altitude excursion occurred). [We needed] strict compliance with SOP that requires absolute verification of vertical and lateral assignments. While we both verified our altitude assignment by calling it back to Center and each other; we both allowed ourselves to be distracted at a critical moment. The lack of confirmation in the FMA and MCP window caused the pilot failure. I never returned my focus back to the MCP altitude window after I allowed myself to be distracted. I also assumed that the pilot flying was actually selecting 39;000 in the window as I went 'heads down'. The pilot flying allowed himself to be distracted to the point that he selected the wrong altitude in the MCP window. One simply HAS to verify the assignment is actually completed in the FMA and the MCP. DO NOT allow yourself to be distracted!
A B737 crew requested FL390 as the final altitude but became distracted and failed to set the MCP or FMC which resulted in climb to FL399.