My question specifically is: When a controller assigns a speed reduction to a flight, without any further details in the clearance, how quickly, time wise is the controller expecting the flight to be established at that speed?
That's kind of a tough question, and I think the answer would depend on the situation. In most cases, speed adjustments are made when sequencing aircraft for an approach...therefore, prompt compliance is desireable. The ATC procedures and guidelines governing speed restrictions can be found here:
http://www.faa.gov/ATPUBS/ATC/Chp5/atc0507.htmlHere is an excerpt:
Section 7. Speed Adjustment 5-7-1. APPLICATION Keep speed adjustments to the minimum necessary to achieve or maintain required or desired spacing. Avoid adjustments requiring alternate decreases and increases. Permit pilots to resume normal speed when previously specified adjustments are no longer needed.
NOTE-It is the pilot's responsibility and prerogative to refuse speed adjustment that he/she considers excessive or contrary to the aircraft's operating specifications.a. Consider the following when applying speed control:
1. Determine the interval required and the point at which the interval is to be accomplished.
2. Implement speed adjustment based on the following principles.
(a) Priority of speed adjustment instructions is determined by the relative speed and position of the aircraft involved and the spacing requirement.
(b) Speed adjustments are not achieved instantaneously. Aircraft configuration, altitudes, and speed determine the time and distance required to accomplish the adjustment.
3. Use the following techniques in speed control situations:
(a) Compensate for compression when assigning air speed adjustment in an in-trail situation by using one of the following techniques:
(1) Reduce the trailing aircraft first.
(2) Increase the leading aircraft first. [/list:u]
(b) Assign a specific airspeed if required to maintain spacing.
(c) Allow increased time and distance to achieve speed adjustments in the following situations:
(1) Higher altitudes.
(2) Greater speed.
(3) Clean configurations. [/list:u]
(d) Ensure that aircraft are allowed to operate in a clean configuration as long as circumstances permit.
(e) Keep the number of speed adjustments per aircraft to the minimum required to achieve and maintain spacing.
b. Do not assign speed adjustment to aircraft:
1. At or above FL 390 without pilot consent.
2. Executing a published high altitude instrument approach procedure.
3. In a holding pattern.
REFERENCE-FAAO 7110.65, Holding Instructions, Para 4-6-4.4. Inside the final approach fix on final or a point 5 miles from the runway, whichever is closer to the runway.
c. At the time approach clearance is issued, previously issued speed adjustments shall be restated if required.
d. Approach clearances cancel any previously assigned speed adjustment. Pilots are expected to make their own speed adjustments to complete the approach unless the adjustments are restated.
e. Express speed adjustments in terms of knots based on indicated airspeed (IAS) in 10-knot increments. At or above FL 240, speeds may be expressed in terms of Mach numbers in 0.01 increments for turbojet aircraft with Mach meters
(i.e., Mach 0.69, 0.70, 0.71, etc.).
NOTE-1. Pilots complying with speed adjustment instructions should maintain a speed within plus or minus 10 knots or 0.02 Mach number of the specified speed.
2. When assigning speeds to achieve spacing between aircraft at different altitudes, consider that ground speed may vary with altitude. Further speed adjustment may be necessary to attain the desired spacing.