Date: 201911
Local time of day: 0601-1200
Location: LGA.Airport, NY
Flight conditions: VMC
Aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B LGA
ATC / advisory: Tower LGA
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Training / Qualification
Second reporter function: Captain; Pilot Flying
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: On the downwind or base vector; the controller advised us to expect direct CHNZO for the RNAV 13 at LGA. I didn't understand what he said and queried the Captain. We found the fix on the approach plate. Shortly thereafter approach cleared us direct CHNZO which was not in the FMS. We entered it manually. A couple miles outside of MEATZ the tower asked if we were tracking the approach okay. He said the approach controller was asking. I looked at the approach plate and saw 232 degrees from CHNZO to RABBY and then 179 degrees to MEATZ. We were flying a course closer to 200 degrees to MEATZ. I verbalized this to the Pilot Flying while we continued to configure. We were VMC and continued the approach. The Captain suspected that RABBY dropped out of the FMS. We failed to ensure all the approach fixes were still in the FMS after adding a fix. We also deleted a discontinuity after added CHNZO. The FMS could have sequenced causing us to delete RABBY. I failed at cross checking the aircraft path against the approach plate. This event is a strong reminder for me to be more vigilant when making changes to the FMS during the approach phase. I could also reduce the workload by having all the approach fixes loaded until we know where the aircraft will intercept the approach path. I will also work to improve my monitor/crosscheck skills in order to make sure the aircraft path matches the approach plate.


Second narrative: Was flying the RNAV-GPS 13 approach into LGA given vectors north of field then direct to CHNZO. Had briefed and verified approach and all waypoints. When CHNZO was entered into the direct to page and selected; a discontinuity showed up after it was entered. Discontinuity was cleared but I believe the waypoint sequence moved up just as the clear button was pushed and deleted RABBY. Aircraft then flew CHNZO direct to MEATZ. Was day VFR but real windy and bumpy. I was looking more outside than inside but had final approach in NAV displayed. Tower queried that Approach Control wanted to know if we were on course. We said yes not realizing waypoint was missing until we were just about at MEATZ. Tower cleared us to land and we had a normal landing. We failed to determine after entering a new waypoint that approach was still sequenced correctly using our challenge and response methodology. First Officer is fairly new on this aircraft and I should have been more diligent in monitoring our workload during this event. The approach is very compressed and we were vectored in very close to the initial approach fix before being cleared for the approach which contributed to our high workload during this event and subsequent task saturation.


Synopsis: Flight crew reported using incomplete FMC programming after receiving a vector to a different initial fix on an RNAV-GPS approach.