B737 flight crew arriving ATL is cleared to fly the CANUK7 RNAV with the north transition; after having set up for the south transition. This last minute change and the required FMC work lead the crew to descend without clearance.
Synopsis
B737 flight crew arriving ATL is cleared to fly the CANUK7 RNAV with the north transition; after having set up for the south transition. This last minute change and the required FMC work lead the crew to descend without clearance.
Narrative
Cleared the CANUK Arrival into ATL. As we descended from altitude to cross CANUK at 14000 FT; we were told to 'expect landing 8 left; fly the 8 left transition.' Since we were arriving from the south; we had set up the FMS for a south landing. The First Officer changed the runway to 8L; and selected the proper transition. As we crossed CANUK; the First Officer asked me what the bottom altitude on the chart was for the arrival; and I said 4000 FT and set 4000 FT in the altitude window. As we left 14000 FT for 12000 FT at the net point; we were given a frequency change. The Controller was surprised that we were descending and had us stay at 12000 FT. Later on the arrival we were instructed to call center upon arrival at our gate. The rest of the approach and landing were uneventful. I called the Operations Manager at the number given; and we discussed the problem. No traffic separation problems were noted; and he just wanted to clarify the situation. The manager did explain the continuing problems they are experiencing with this arrival. I do know the difference between 'fly the transition' and 'descend on the transition.' As the Captain; I am responsible; and I accept full responsibility; for the actions of my aircraft and crew. This will not happen again in my aircraft. I have two suggestions to help us with this arrival. 1) If there is any way to assign the transition earlier in the descent; it would cut down considerably in the cockpit workload. We were given this change as we leveled off at Canuk; dealing with the resulting discontinuity in the FMS; and checking the points and altitudes against the paper chart. Managing all three issues at exactly the same time contributed to our confusion regarding the clearance. 2) If the Controllers would state 'fly the 8L transition; maintain 14000 FT;' there would be no confusion. As we became task saturated when our workload increases; we remember the last number we hear. I am now convinced we would not have descended out of 14000 FT had these two words been added to the clearance. For my part; I will strive to never let cockpit workload get in the way of aircraft safety. In the future; I will clarify any questions I may have regarding a clearance.
Second reporter narrative
Arriving on the CANUK to ATL landing to the east. I briefed the visual backed up by the ILS to Runway 10 with a back up of the same approach to 9R. I did not brief or discuss landing on the north side. Well into the arrival; nearing CANUK at 14000 FT we are instructed by approach to fly the transition to 8L. I look at the approach plate and see we don't have a lot of time to make the split and head NW. There are also several different altitudes on the arrival to 8L. I decide I have time to put the 8L transition in the FMS with autopilot on at 14000 FT and begin to do so. We have passed CANUK and the next altitude is 12000 FT and then 7000 FT. The Captain rolls in the lower altitude. I am still working on clearing some excess points out of the FMS; we have made the turn to the northwest. I ask the Captain if we are cleared to descend after he puts in the lower altitude. I have a feeling something isn't quite right. He says yes; we are cleared for the transition. I react poorly and do not ask for verification from the Controller. The Captain was changing the radios and MCP while I verified the FMS and began briefing the new arrival runway. We are busy. As we approach 12000 FT; Approach Control queries us on our altitude. We were not cleared to descend from 14000 FT. The clearance I heard was 'cleared for the 8L transition'. I had not heard what I needed to hear to descend; cleared to descend via the 8L transition. This is my error and I should have not left 14000 FT without proper clearance. I would add that the lateness of clearance to the 8L transition allowed little time to properly process and interpret the clearance we were given. We had been up approach for several minutes and had no indication of landing runway or a requirement to land on the north side. All that said; I definitely now better than to get caught like this.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.