Wake turbulence: ATC separation intervals and pilot waivers
No radar vectoring (non-surveillance): ATC spaces wake-turbulence departures by time, not distance (TC AIM RAC 4.1.1).
| Preceding | Following | Circumstance | Interval |
|---|---|---|---|
| known heavy | any aircraft | takes off from threshold of same runway or of parallel runway less than 2 500 ft away | 2 min |
| known medium | light | the 2 min circumstances | Exception: no fixed interval, only a wake turbulence advisory |
| known heavy | any aircraft | starts roll from intersection or point further along the runway than preceding; or controller believes follower needs more runway length than preceding | 3 min |
| known medium | light | conditions of 3 min heavy row | 3 min |
| preceding heavy | follower | its projected flight path will cross the heavy's | up to 3 min |
- ATC cannot guarantee no wake turbulence, even with intervals.
Denial and advisory:
- Takeoff clearance denied solely for wake turbulence: tower controller must advise pilot why, stating type and position of the wake-creating aircraft.
- Purpose: pilot can weigh waiving the requirement.
Pilot waivers:
- Controllers may not initiate a waiver.
- Controller issues takeoff clearance to pilot who waives on own initiative, except when follower is light or medium and:
- starts takeoff from an intersection, or a point significantly further along, behind a heavy; or
- departs after a heavy takes off or makes a low or missed approach in the opposite direction on the same runway; or
- departs after a heavy makes a low or missed approach in the same direction on the same runway.
- VFR waiver: pilot accepts responsibility for separation; controller still issues wake turbulence cautionary with clearance.
- IFR departures: controller stays responsible for minima.
Trap: the three waiver exceptions are where ATC still refuses clearance after the pilot waives.
References
- TC AIM RAC 4.1.1