Air carrier flight crew reported descending below the published altitude due to inattention to the selected automation. The crew added that ATC was reporting there was GPS jamming in the DFW area at the time.
Synopsis
Air carrier flight crew reported descending below the published altitude due to inattention to the selected automation. The crew added that ATC was reporting there was GPS jamming in the DFW area at the time.
Narrative
Arriving into DFW we were first given a descent to FL240 and told to maintain at least 1200 FPM. So FO (First Officer) selected 1200 FPM in the VS. Before leveling at FL240 we were handed off and given a descend via for the Boove arrival. We both confirmed 12;000 ft. was entered into the altitude select but neither of us noticed that 1200 FPM was still selected on the VS. We were briefing the approach at that time. We were having a fairly lengthy discussion of the fact that the ILS was OTS (Out of Service) and there was GPS jamming going on that was affecting the aircraft at the time. Controllers had told us to expect that jamming to continue for 'quite awhile'. So we were not sure if the aircraft would recover from the jamming and if that would affect the RNAV approach - it was VFR at the time so we would be doing a visual but wanted to brief a backup. Approaching the GIBLT intersection we both noticed the aircraft had descended below the lowest altitude for GIBLT by about 2;000 ft. We leveled the aircraft off and reselected managed and continued uneventfully from that point. The Controller never stated anything about out altitude and we were only below the required altitude for a couple minutes at the most. Distraction was the main cause of this. At least one of us should have noticed the aircraft was not in a managed descent. FO had just over 100 hours in type even though he had come off the Aircraft X and is a more than capable pilot. When clearances are given all parameters should be checked to make sure the clearance is properly managed.
Second reporter narrative
During the decent on BOOVE6; the first crossing restriction at the GIBLT intersection (between FL240 and FL300) was not complied and the actual crossed altitude was around FL220. In the middle of an arrival briefing; the ATC cleared us to descend and maintain FL240 with the decent rate more than 1200 FPM. The vertical speed was set to 1500 FPM and the briefing was continued. The decent via clearance was received soon after but we failed to switch and monitor a decent mode because we were still in the middle of a briefing. Just prior to the GIBLT intersection; we realized that we were below FL240 and immediately leveled off at FL220. The flight was continued to descend via the arrival without further event.Cause: Failures to monitor a descent mode and a task saturation during the briefing can be a role in the event. Suggestion: This event could have been prevented if the arrival briefing had been completed prior to starting of a descent. Also; the descent mode must be monitored carefully.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.