Citation X (C750)
Communication Breakdown; Situational Awareness; Fatigue
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
General None Reported / Taken
Human Factors
Second leg of day. Flying from ZZZ to ZZZ1. Pilot Flying was FO (First Officer); I was the Pilot Monitoring although the Captain. Weather was VMC. ZZZ1 was landing RWY XXL utilizing RNAV XX Z. We flew the approach utilizing RNAV procedures; Vertical Speed; with altitude settings set for each altitude restriction. All altitude restrictions and procedures were briefed according to standard briefing card.  Prior reaching the final approach fix at 2;400 ft.; we set the LNAV MDA for the approach which was 1;020. Upon reaching the FAF; we began our descent to the MDA looking toward ZZZZZ as the MAP. Upon arriving at MDA; the runway was clear in visual sight approximately 4 NM; the flying pilot concentrated on maintaining the final approach course which is offset by 11 degrees. Ride was light to moderate turbulence. We never went below MDA. At this point; we were given a low altitude alert by Tower; we acknowledged this radio call and climbed higher above MDA. We were then given our landing clearance behind a B737; and landed with no further issues. Upon review on ground of our FMS waypoints; we only saw loaded ZZZZZ1; ZZZZZ2; ZZZZZ. Upon review of the approach plate; we then noted ZZZZZ3 (a fix inside the FAF) which had a altitude restriction of 1;240 which is 1.6 NM from MAP and 2.9 NM from Runway XX. Although we briefed that restriction at cruise altitude; during the business of the ZZZ airspace arrival; traffic; and busy; gusty approach; we both mistakenly utilized the loaded FMS waypoints. Not having ZZZZZ3 in our FMS provided us a false assumption we could come down directly to the MDA. This is what drew the low altitude alert from Tower I believe. Again; we were also VMC with my eyes outside ensuring we could also line up with runway.In my opinion; we simply missed this altitude restriction at ZZZZZ3. Despite out best efforts to brief and understand the GPS approach; we failed to remember this during the actual approach. We also failed to back ourselves up by perhaps placing this additional fix into the FMS. I could have also chose to use VNAV knowing the weather. This was the second flight of the day; at end of a day at night - rolling fatigue was a probable issue as well.
Citation pilot reported the stepdown fix inside the Final Approach Fix was not entered in the FMS; which resulted in missing the stepdown altitude restriction and ATC issuing a low altitude alert.