Large Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Situational Awareness
ATC Issue All Types; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Procedure; ATC Equipment / Nav Facility / Buildings; Environment - Non Weather Related; Human Factors
Winds were calm at ROA.  ATIS called Runway 24 as landing and departing using RNAV (RNP) Z RWY 24.  ATC asked us if we wanted the visual.  Given terrain and having never been to ROA I elected to stay with the RNAV approach.   ATC had us cross STEFN at 5;400 feet which had us 400 ft high.  We attained VNAV PATH and 150 KIAS approximately 3 miles after STEFN.   Since we could see the terrain and visibility was greater than 5 miles we planned to maintain 150 KIAS until 5 miles prior to the airfield.   Between DBERD and WILHE there is depicted terrain with a spot elevation 2;058 feet.  Just pass that terrain; still on LNAV and VNAV PATH at 150 KIAS Roanoke Tower gave us a low altitude warning. We verified both our altimeter settings and altitude.  We advised Tower that we could see both terrain and the airfield.  Tower acknowledged and advised us that they could see us clearly; and that they were required to announce the low altitude alert anytime it is activated.  Otherwise; the approach and landing were normal.  Of note there was no GPWS alert with flaps 20 and gear up.  After block-in; I requested a phone number to discuss the event.I spoke with [ATC] and inquired about the altitude alert call.  He indicated they sometimes get an altitude alert activation; but usually on vectors to visual Runway 24. He also indicated he was not as familiar with the Tower sector.   I asked him to look into it a bit more given that the only difference between what I flew and what I would have flown in IMC is I would have been 25 KIAS slower which would have resulted in a descent rate difference of just 133 FPM given a constant wind.  The wind in this case was a light headwind during the approach.Had I been in IMC and/or could not immediately determine by visual reference terrain clearance; the approach would have terminated with an immediate climb and terrain escape maneuver.Recommend the altitude alert system be de-conflicted to ensure aircraft on FMS glide path for the RNAV Z RWY 24 do not get erroneous alerts and/or note on company chart outlining requirements for speed on the approach or other requirements to successfully complete the approach in IMC.No deviations noted by Tower or aircrew.  The low altitude alert system may need to be adjusted or approach procedures may need to be adjusted to avoid erroneous low attitude warnings.De-conflict low altitude warning with proper approach lateral and vertical guidance.
Air carrier Captain reported receiving a low altitude alert from ATC on approach into ROA even though it appeared there was no terrain conflict.