6.8 Horizontal Speed Control instructions

6.8.1 Flight crews should be given adequate notice of planned speed control, because application of speed control over a long period of time may affect aircraft fuel reserves.

6.8.2 Speed control shall not be applied to aircraft entering or established in a holding pattern.

6.8.3 Speed adjustments should be limited to those necessary to establish and/or maintain a desired separation minimum or spacing.

6.8.4 Instructions involving frequent changes of speed, including alternate speed increases and decreases, should be avoided.

6.8.5 The flight crew shall inform the ATC unit concerned if at any time they are unable to comply with a speed instruction. In such cases, the controller shall apply an alternative method to achieve the desired spacing between the aircraft concerned.

6.8.6 At levels at or above FL250, speed adjustments should be expressed in multiples of 0.01 Mach; at levels below FL250, speed adjustments should be expressed in multiples of 10kts based on IAS.

Note 1: Mach 0.01 equals approximately 6kts IAS at higher flight levels.

Note 2: When an aircraft is heavily loaded and at a high level, its ability to change speed may, in cases, be very limited.

6.8.7 Aircraft shall be advised when a speed control restriction is no longer required.

METHODS OF APPLICATION

6.8.8 In order to establish a desired spacing between two or more successive aircraft, the controller should first
either reduce the speed of the last aircraft, or increase the speed of the lead aircraft, then adjust the speed(s) of the other aircraft in order.

6.8.9 In order to maintain a desired spacing using speed control techniques, specific speeds need to be assigned to all the aircraft concerned.

Note 1: The TAS of an aircraft will decrease during descent when maintaining a constant IAS.
When two descending aircraft maintain the same IAS, and the leading aircraft is at the lower level, the TAS of the leading aircraft will be lower than that of the following aircraft.
The distance between the two aircraft will thus be reduced, unless a sufficient speed differential is applied.
For the purpose of calculating a desired speed differential between two succeeding aircraft, 6kts IAS per 1 000ft height difference may be used as a general rule.
At levels below FL080 the difference between IAS and TAS is negligible for speed control purposes.

Note 2: Time and distance required to achieve a desired spacing will increase with higher levels, higher speeds, and when the aircraft is in a clean configuration.

6.8.10 An aircraft should, when practicable, be authorized to absorb a period of notified terminal delay by cruising at a reduced speed for the latter portion of its flight.

6.8.11 An arriving aircraft may be instructed to maintain its “maximum speed”, “minimum clean speed”, “minimum speed”, or a specified speed.

Note 3: “Minimum clean speed” signifies the minimum speed at which an aircraft can be flown in a clean configuration, i.e. without deployment of lift-augmentation devices, speed brakes or landing gear.

6.8.12 Speed reductions to less than 250kts IAS for turbojet aircraft during initial descent from cruising level should be applied only with the concurrence of the flight crew.

6.8.13 Instructions for an aircraft to simultaneously maintain a high rate of descent and reduce its speed should be avoided as such manoeuvres are normally not compatible. Any significant speed reduction during descent may require the aircraft to temporarily level off to reduce speed before continuing descent.

6.8.14 Arriving aircraft should be permitted to operate in a clean configuration for as long as possible. Below FL150, speed reductions for turbojet or fanjet aircraft should not be less than 220kts IAS, which will normally be very close to the minimum speed of turbojet aircraft in a clean configuration, may be used.

6.8.15 Only minor speed reductions not exceeding plus/minus 20kts IAS should be used for aircraft on intermediate and final approach.

6.8.16 Speed control should not be applied to aircraft after passing a point 4nm from the threshold. (Final approach)