GM1 to AMC1 ATS.TR.210(a)(3) Operation of air traffic control service

HORIZONTAL SPEED CONTROL INSTRUCTIONS — GENERAL

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

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

(c)The true airspeed (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, 11 km/h (6 kt) IAS per 300 m (1 000 ft) height difference may be used as a general rule. At levels below 2 450 m (FL 80), the difference between IAS and TAS is negligible for speed control purposes.

(d)The 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 (see point (b) of GM1 to AMC2 ATS.TR.210(a)(3))).