According to FAA rules, controllers are required to hold aircraft 2 or 3 minutes for wake turbulence under certain conditions. When is that wake turbulence hold required, and when are pilots allowed to waive it? What is the correct way to request a waiver?
The AIM 7-3-9 lists the required separations. Behind a heavy aircraft, the departure hold is 3 minutes and it may not be waived. Behind a small aircraft, the hold may be waived on pilot request only:
3. Additionally, appropriate time or distance intervals are provided to departing aircraft:
(a) Two minutes or the appropriate 4 or 5 mile radar separation when takeoff behind a heavy/B757 jet will be:
(1) From the same threshold.
(2) On a crossing runway and projected flight paths will cross.
(3) From the threshold of a parallel runway when staggered ahead of that of the adjacent runway by less than 500 feet and when the runways are separated by less than 2,500 feet.
NOTE- Controllers may not reduce or waive these intervals.
b. A 3-minute interval will be provided when a small aircraft will takeoff:
1. From an intersection on the same runway (same or opposite direction) behind a departing large aircraft,
2. In the opposite direction on the same runway behind a large aircraft takeoff or low/missed approach.
NOTE- This 3-minute interval may be waived upon specific pilot request.
c. A 3-minute interval will be provided for all aircraft taking off when the operations are as described in subparagraph b1 and 2 above, the preceding aircraft is a heavy/B757 jet, and the operations are on either the same runway or parallel runways separated by less than 2,500 feet. Controllers may not reduce or waive this interval.
EDIT: The AIM 4-3-10(f) (intersection takeoffs) also addresses this question, including suggested pilot phraseology for waiving the hold (emphasis mine):
Controllers are required to separate small aircraft (12,500 pounds or less, maximum certificated takeoff weight) departing (same or opposite direction) from an intersection behind a large nonheavy aircraft on the same runway, by ensuring that at least a 3-minute interval exists between the time the preceding large aircraft has taken off and the succeeding small aircraft begins takeoff roll. To inform the pilot of the required 3-minute hold, the controller will state, “Hold for wake turbulence.” If after considering wake turbulence hazards, the pilot feels that a lesser time interval is appropriate, the pilot may request a waiver to the 3-minute interval. To initiate such a request, simply say “Request waiver to 3-minute interval,” or a similar statement. Controllers may then issue a takeoff clearance if other traffic permits, since the pilot has accepted the responsibility for wake turbulence separation.
Wake turbulence in general is considered a key safety issue by the FAA and there is a large amount of information in the AIM, the ATC guide and elsewhere.