Date: 202002
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Aircraft: Q400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: GPS & Other Satellite Navigation
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance; Flight Crew FLC Overrode Automation
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Captain and FO (First Officer) on 4th and last leg of second day of trip; flight XXXX to ZZZ. Flight crew had agreed to maximize RNAV approaches on trip for proficiency. On preflight at ZZZ1 RNAV (GPS) Rwy XX Approach was programmed into FMS2 by FO. FMS1 cross filled from FMS2. At cruise during approach briefing it was jointly agreed to fly full RNAV (GPS) Rwy XX Approach via [initial approach fix] transition flying hold in lieu (i.e. not activating approach and requesting vectors to final). PF (Pilot Flying) directed PM (Pilot Monitoring) to request direct IAF from ATC. Clearance direct to IAF was given by ATC and flight crew set up VNAV profile to waypoint altitudes on the approach. Since Hold In Lieu was seldom practiced; PM and PF discussed how the FMS waypoints should present themselves on the Flight Plan page and Clearance Page of FMS. Hold was noted at IAF waypoint [holding fix]. The Hold in Lieu was discussed at length by the flight crew. PM brought Holding Definition up on PM's FMS which indicated a 'parallel' entry. Flight Crew discussed what to expect with a parallel entry to Hold in Lieu and expected a left turn when reaching the 'fly-over' waypoint. Flight Plan page was brought up on both FMSs to ensure waypoints matched.Approach Control cleared flight for the approach and if I recall correctly gave a crossing altitude of 6;000 or higher at IAF. After approach clearance was received and IAF restriction was ensured; the altitude alerted was set to field elevation. As briefed; PF slowed airplane to 200 KIAS prior to capturing [holding fix] in preparation for hold in lieu. Immediately following capture of fly-over waypoint aircraft made standard rate turn to the RIGHT instead of LEFT. Both Pilots were immediately aware the maneuver was the opposite direction of the expected maneuver that was briefed. PF began brief troubleshooting the FMS when airplane began a turn to the LEFT after turning approximately 60 degrees to the RIGHT. Aware of the terrain east of ZZZ; PM requested vectors from ATC to insure terrain clearance. Best estimate from onset of unexpected maneuver to calling ATC for vector away from terrain was approximately 20 seconds. Approach Control directed turn to 275. At this point 275 was about at the airplanes 6 O'clock position so PM elected to continue left turn using heading bug and HDG mode was selected. PM requested direction for turn from ATC and a RIGHT turn was directed as well as a climb to 6;000 feet. PF disconnected the autopilot and began a right turn to 275 and climb to 6;000 feet. Later; Approach Control directed a climb to 8;000 feet and enquired if we would like vectors to final for the ILS approach to Rwy XX. PF and PM both agreed to switch to an ILS approach. Although not discussed; I believe we both felt after the unexpected maneuver it unwise to double down on another RNAV XX Approach even if we intended to activate the approach and receive vectors to final. While still hand flying; PF directed PM to push STBY on FMCS and auto flight with autopilot in heading mode was re-established from clean state. PM loaded ILS approach to XX and this ILS approach was setup; briefed and conducted uneventfully.Recommend warning against any flight crews flying the full RNAV (GPS) Rwy XX Approach to ZZZ until the FMS anomaly above is understood. Recommend testing the RNAV (GPS) Rwy XX Approach at ZZZ in the simulator by attempting to duplicate the scenario described above. Pilots did not inadvertently disarm the approach prior to [holding fix]. There is no STAR into ZZZ so issues with setting up a contiguous RNAV Approach from a STAR did not exist for the scenario that played out. Crew was cleared direct to a transition waypoint and attempted to fly the full approach including turn in Lieu as selected from Approach list in the FMS (i.e. no modifications where made to any part of the canned FMS approach).




Synopsis: Q400 Captain reported aircraft automation executed wrong track entering holding pattern.