An Approach Controller and a flight crew arriving SLC describe the circumstances surrounding a descent below assigned altitude and a conflict with a departing aircraft.
Synopsis
An Approach Controller and a flight crew arriving SLC describe the circumstances surrounding a descent below assigned altitude and a conflict with a departing aircraft.
Narrative
A CRJ9 was on the LEEHY Arrival to SLC. I cleared the CRJ direct DRYVR with a descent to 17;000 FT to sequence in front of traffic over JAMIN. I then issued a descent to 15;000 FT to the CRJ. I needed more room; so I re-cleared the CRJ direct to PITTT and resumed the arrival for Runway 16R with the last assigned altitude of 15;000 FT. There was a departure off SLC level at 13;000 FT southbound. I was briefing the Handoff Controller with the sector information and traffic when I noticed the CRJ leaving 13;900 FT crossing in front of the departure. I turned the CRJ to 250 heading; climbed to 15;000 FT; and issued traffic. The departure had my arrival in sight and was instructed to maintain visual separation. The conflict alert never went off. The CRJ went down to 13;100 FT on a 250 heading to get more separation before climbing back up to 15;000 FT. The CRJ was never cleared to descend via the LEEHY 3 Arrival. I think when I re-cleared the CRJ direct PITTT they assumed they had a descent to 11;000 FT; which is the altitude they would descend to with restrictions if they were cleared to descend via the LEEHY 3 Arrival.When I re-clear an aircraft that was on a RNAV arrival direct a new fix on that arrival; [I should] restate an altitude no matter if it is the same altitude that was previously issued.
Second reporter narrative
On the descent; we checked on with ATC and were told of a new ATIS. The First Officer had to leave the frequency to get the ATIS since our ACARS printer was inoperative. I assumed she was monitoring (she was; but had the volume turned down) so I wasn't paying as close attention to ATC instructions as I should have. I heard a clearance to 13;000 FT issued; rolled it into the altitude; and asked for confirmation. For some reason (not sure why) I started to descend without her confirmation. When she queried me; I was sure I heard the clearance and answered in the affirmative. I had expected her to read it back (because she was monitoring the frequency); so when she queried if I read back the instructions; I said no. She attempted a couple of read backs and was not acknowledged. At this point we were about to level at 13;000 FT and traffic was obviously climbing through our altitude. She pointed this out as well. I realized my mistake; but it was way too late and ATC issued a climb back to 15;000 FT as well as a turn to 280.I was kind of 'zoning out' a bit on the descent and I assumed we were both in the loop on COMM 1. For some reason I thought I heard a clearance to 13;000 FT and I started the descent without a confirmation. I rolled the altitude down; put my finger on the knob; and even said 'confirm;' but I didn't wait for her to actually CONFIRM the altitude. Furthermore; when she queried me; instead of starting down I should have leveled at 15;000 FT (there was plenty of time; the plane was only just starting down) and confirmed with ATC. Honestly; this is my normal 'SOP' anytime there is a question with my First Officer; I wait until we confirm with ATC before executing the instruction. I think I was a bit preoccupied because I had caused some irritation with the First Officer during the initial descent into SLC airspace. The mood in the flight deck changed perceptibly after that. Of course; after this screw up during the descent I felt even worse. We had a good trip; with excellent rapport; and to end it like this really sucked.I need to make sure I do not waver from my rule of confirming with ATC when there is disagreement. I implemented this rule as a result of a previous [mistake] and it has served me really well. I'm honestly not sure why I deviated from it; but it won't happen again. I know sometimes my confirmations sound anal or irritating; and maybe that's what I was worried about; but I can't remember that even crossing my mind. I think I was just kind of zoned out; in familiar airspace; the flight deck was sterile and quiet; and I was over-confident and excited to be on the last day of a four day. Still; there is no excuse. I screwed up; broke my own rule and it bit me...hard.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.