Date: 202109
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Confusion; Workload; Troubleshooting; Time Pressure
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Air Traffic Control; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Human Factors; Procedure; Environment - Non Weather Related
Primary problem: Ambiguous

Narrative: Initially set for ZZZZZ ONE arrival to ZZZ. Runway XX active so they had to re-clear us on the ZZZZZ1 TWO. Center asked us to go direct to ZZZZZ2 and keep 290 or greater as we were out front of other traffic. Approach told us to go direct ZZZZZ2; cross ZZZZZ2 at 11;000 feet and cleared for RNAV GPS X XXR. The clearance of DIRECT ZZZZZ2 put us 90 degrees off the outbound course from ZZZZZ2. ZZZZZ2 is a fly-over fix. We arm the approach and cross over the top of ZZZZZ2 at 11;000 feet and the plane turns north and begins decent to next altitude. Approach calls us and says they have a low altitude alert on use as we were now below the minimum vector altitude for that area.  She asks if we missed the turn and I said 'No'; that the aircraft has a turn radius as we are turning to the north. She said minimum vector altitude was 10;900 feet and we were at 10;300 feet. We stopped our descent and the aircraft dropped out of the approach mode. Approach asked if we had the terrain insight; luckily for us it was clear with 10 mile visibility and we could see cultural lighting on the hills and knew terrain was not an immediate factor. None of the Enhanced Ground Proximity Warning System annunciated and we were always in either the black or hashed green on the ND. Back on the inbound course; we selected a lower altitude and armed the approach. Nothing further.Center gave us a speed and we didn't get relief until we asked Approach. This higher speed resulted in a larger turn radius than had we been at the mandatory 210 knots restriction at ZZZZZ2. They also gave us direct to a Fly-Over fix with a 90 degree intercept; which set us up to fly through our final approach course; and asked us to cross ZZZZZ2 at 11;000 feet instead of the mandatory +13;000 feet restriction.   This was all done to keep the other aircraft from getting a vector or slowing down. Don't give direct to a fly-over fix with 90 degrees of turn required at the fix; especially at night; at lower than published altitude; and in mountainous terrain.




Synopsis: Air Carrier Captain reported receiving a Low Altitude Alert from Approach Control. The Captain stated that ATC assigned a higher than normal speed; creating a wider arc during a turn involving a Fly Over Fix; and the aircraft could not stay within the approach boundary.