In the US, if assigned a heading to fly, we are not expected or permitted to apply a wind correction and fly a track instead. If a procedure has a DR heading leg, we fly the heading and the TERPS has already considered a planned worst case wind effect from the point of view of obstacle clearance. When operating at a towered airport with parallel runways and given instructions to fly runway heading, we are expected to fly a heading that corresponds to the runway magnetic alignment. Two aircraft departing from parallel runways will maintain separation from each other if they both fly the heading. If the down wind aircraft decides to fly a track, they can cause separation to be lost and get too close to the aircraft on the upwind parallel who is following instructions and flying a heading. If the initial leg is part of a SID or ODP and includes a course or track, then that is flown as a track. I don’t ever recall receiving a departure clearance from a towered airport in the US to fly a track that is not part of a procedure.
The PCG is perfectly clear for FAA ops:
RUNWAY HEADING- The magnetic direction that corresponds with the runway centerline extended, not the painted runway number. When cleared to “fly or maintain runway heading,” pilots are expected to fly or maintain the heading that corresponds with the extended centerline of the departure runway. Drift correction shall not be applied; e.g., Runway 4, actual magnetic heading of the runway centerline 044, fly 044.
QuoteTwo aircraft departing from parallel runways will maintain separation from each other if they both fly the heading.
If they are flying at the same level and the same speed, yes. But not if the faster one is overtaking the slower one. The linear crosstrack drift will depend on how long the aircraft has been airborne, and so the original separation will be reduced by the crosswind velocity times the difference in airborne time. That could easily be half a mile. So I think any controller who wanted to ensure separation would give you a number to fly, and adjust it as necessary.
The fact that there is any debate about this is a good reason to avoid the instruction in any circumstances where it matters, to the precision of the drift angle, what the pilot does.
I agree that if it matters, one of the aircraft will be assigned a new heading, but not a track. In the vast majority of the cases, the speeds will be matched close enough and the runway spacing will provide for separation. Some airports such as at KSFO will stagger departures off of the parallel runways because they are too close to one another.
