Date: 201810
Local time of day: 0001-0600
Location: SMF.Airport, CA
Flight conditions: VMC
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: TRACON NCT
Aircraft component: FMS/FMC
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Human-Machine Interface; Workload; Situational Awareness
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Descending on the final portion of the RNAV arrival we were set up for and briefed to do a Visual Approach backed up by the RNAV-Z Approach. There were points on the approach that would not load until we selected NO STAR on the FMS. For situational awareness; I selected NO STAR but did not insert the change so that the points would show up on the plan view but the active flight plan would continue to be the Arrival. The Captain communicated that one of the last fixes on the STAR coincided with one of the IAF/IF's on the RNAV-Z Approach. We agreed on the plan to navigate toward that fix once cleared for the Visual Approach and use the FMS guidance to back up the Visual. During that communication; the Captain accidentally inserted the changes into the FMS thereby dropping the arrival out of the FMS and putting us into heading mode instead of on the RNAV STAR. I called ATC and informed them that we were having a NAV issue and requested a heading and descent clearance. They provided us with a heading and to descend to 4000 feet. They mentioned that we were the second aircraft to have a navigation issue on that arrival today and asked for clarification on the issue. I informed them that we accidentally dropped fixes out of our FMS while we were sequencing points on the approach. We were subsequently cleared for the Visual Approach and landed without further incident. This event occurred because we were in a high workload environment and had a quick accidental keystroke. As a result a large navigation change occurred in the FMS. Ordinarily this couldn't have happened with only one keystroke but we were using a situational awareness tool to gain perspective on the upcoming approach. We were both carefully monitoring the flight path so the error was quickly trapped but it was too late to stay on our original clearance. I believe that the key to not repeating this is to include a briefing point if ever preemptively loading a series of points but not inserting them. When I loaded those points; I should have said explicitly; 'Do not insert this change or it will drop our arrival.' The Captain understood that but including that in our communication would have brought it to front of mind to hopefully prevent this error. Close flight path monitoring and prompt ATC communication was instrumental in preventing this from resulting in loss of separation.




Synopsis: Air carrier First Officer reported the Captain accidentally removed fixes from the FMS while conducting a Visual Approach.