Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion; Situational Awareness
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance
Chart Or Publication; Human Factors; Procedure; Aircraft
Inbound to VIDP the FMS SAM 6F RNAV STAR had been loaded and briefed and was being navigated by the autopilot in the VNAV mode. All indications on the NAV displays were normal for the procedure. As aircraft made the left turn at SAM fix Approach Control assigned us a 090 heading. Additionally they inquired as to which arrival we were assigned and flying. The rest of the arrival was vectors transitioning to ILS Runway 29 which was completed successfully. During taxi in we were instructed to call Approach Control on a land line. After a discussion along the lines of 'all of our company jets were not flying the correct procedural ground track' we concluded the conversation with an agreement to contact Company Sandards to investigate the matter.
The reporter advised that; during the land line call to Approach Control; limited common language skills made it impossible for him to determine exactly where their flight path deviated from where ATC expected them to go. He stated the moving map display coincided perfectly with the charted arrival which indicated to him that; if their track differed from ATC's expectation; the error was programmed into both.The reporter further addressed his concern about having no raw data means by which to confirm the digitally derived track the FMS slavishly follows coincides with the intended real life track over the ground. He referenced his many years of flying from point to point based on land based NAV fixes that did provide such independent assessment of the aircraft's real location with respect to the earth's surface.
A B777-200 Captain was advised by VIDP Approach Control that his lateral track did not conform to the SAM 6F RNAV STAR by which they had been cleared. The reporter; however; disagreed-citing their FMS track was precisely following the FMS magenta line which; in turn; exactly matched the route described on their commercially published aero chart.