A300
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Aircraft; Airspace Structure
This was our fourth consecutive night flying the departure out of ZZZ. On the first night I briefed the FO that in the past; some aircraft initiated the turn at ZZZZZ (Fly-by waypoint) earlier than ATC was expecting. The first three nights in three different aircraft were uneventful. Each aircraft remained within a mile or so of ZZZZZ in the initial turn to ZZZZZ1. While operating in NAV mode; the aircraft initiated the turn prior to ZZZZZ such that it would pass 3 to 4 miles inside the fix. I noticed the turn and advised the FO that this is the early turn I had been referring to and to slow the aircraft in an attempt to mitigate the turn radius. Departure queried us shortly thereafter and stated that we had initiated our turn too early. The controller gave us a heading vector of 300 and an admonishment for the perceived deviation. I advised him that we were operating properly in NAV mode as required for this departure. After a few miles; we were re-cleared direct to ZZZZZ1 and changed frequency. The next controller asked us a series of questions regarding our NAV inputs and whether we had modified the departure in any way. I replied to the controller that we had not; and that this was a known issue that had been occurring on occasion for a number of years; and that some but not all of our Airbus aircraft initiated the turn at ZZZZZ in this fashion. The controller indicated that he had heard of this issue and seemed satisfied with this answer. We were cleared direct ZZZZZ2 and the rest of the flight was uneventful. Uncertain. I had been under the belief that the early turns were perhaps speed related and that by slowing down; it would make the turns more as ATC expected. However; in the preceding three nights we elected to allow the aircraft to fly programed profile speeds and each aircraft made the turns close to the fixes with no issues. This particular aircraft on this night did not. Nor did slowing the aircraft have any appreciable effect on the turn radius the NAV system was planning. I have found no way to predict in advance when this is going to happen.
A300 Captain reported that the aircraft initiated a turn on the SID earlier than ATC was expecting passing inside the fix by 3 to 4 miles.