Narrative:

We were positioning a dfw area airport; I was the pilot flying. We departed and the clearance included direct cqy VOR and the dumpy three arrival to our destination airport. We were assigned FL360 as a final altitude. The departure; climb and cruise portion of the flight were all normal. As we approached the dallas area we were given a descent to FL240; we complied with the clearance and at that time we started the descent checklist and briefed the arrival and destination approach. We were then given a clearance to cross the cqy VOR at 13;000 ft. The pilot not flying plugged the crossing restriction into the FMS. After we verified that what he had plugged in to the FMS was correct; we verified the altitude in the alerter; and then I selected the VNAV function; or at least I thought I did. The pilot not flying continued to set the cockpit up for our arrival. About the time the pilot not flying finished setting up the airplane for arrival; ATC called and asked if we had received a clearance to cross cqy at 13;000 ft. The pilot not flying immediately answered we had not received a clearance. Right after that I looked at the altitude alerter and it showed our assigned altitude as 13;000 ft. I realized at that point we had in fact been assigned a descent clearance and we had not complied with it. Before we could say anything to ATC they assigned us another clearance to cross orvll at 9;000 ft. Which is depicted on the chart what we had briefed originally and were expecting to be assigned. We complied with the clearance immediately and made the crossing restriction without issue. Nothing else was said to us by ATC. I suggest fly the airplane first and then call for and complete other required tasks. Verify that the aircraft is doing what you want it to do when using the automation to fly the aircraft. I thought I had selected the VNAV and the airplane would start down as advertised. I diverted my attention for just a moment to complete other tasks and when I turned back and saw that the aircraft was still level at FL240; I assumed everything was normal. I forgot we had been given a clearance to cross cqy at 13;000 ft until ATC said something and saw that we had in fact put 13;000 ft in the altitude alerter.

Related reports:

Google
 

Original NASA ASRS Text

Title: A Captain reported MCP; FMC programming; and briefing complete for a descent into the DFW area; but after receiving clearance to 13;000 FT he became distracted with other tasks and failed to engage NAV; thus missing the altitude constraint.

Narrative: We were positioning a DFW area airport; I was the pilot flying. We departed and the clearance included direct CQY VOR and the Dumpy Three arrival to our destination airport. We were assigned FL360 as a final altitude. The departure; climb and cruise portion of the flight were all normal. As we approached the Dallas area we were given a descent to FL240; we complied with the clearance and at that time we started the descent checklist and briefed the arrival and destination approach. We were then given a clearance to cross the CQY VOR at 13;000 FT. The pilot not flying plugged the crossing restriction into the FMS. After we verified that what he had plugged in to the FMS was correct; we verified the altitude in the alerter; and then I selected the VNAV function; or at least I thought I did. The pilot not flying continued to set the cockpit up for our arrival. About the time the pilot not flying finished setting up the airplane for arrival; ATC called and asked if we had received a clearance to cross CQY at 13;000 FT. The pilot not flying immediately answered we had not received a clearance. Right after that I looked at the altitude alerter and it showed our assigned altitude as 13;000 FT. I realized at that point we had in fact been assigned a descent clearance and we had not complied with it. Before we could say anything to ATC they assigned us another clearance to cross ORVLL at 9;000 FT. which is depicted on the chart what we had briefed originally and were expecting to be assigned. We complied with the clearance immediately and made the crossing restriction without issue. Nothing else was said to us by ATC. I suggest fly the airplane first and then call for and complete other required tasks. Verify that the aircraft is doing what you want it to do when using the automation to fly the aircraft. I thought I had selected the VNAV and the airplane would start down as advertised. I diverted my attention for just a moment to complete other tasks and when I turned back and saw that the aircraft was still level at FL240; I assumed everything was normal. I forgot we had been given a clearance to cross CQY at 13;000 FT until ATC said something and saw that we had in fact put 13;000 FT in the altitude alerter.

Data retrieved from NASA's ASRS site as of July 2013 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.