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Speed Control

Why control speed

Speed is the cheapest sequencing tool. It adjusts spacing without lengthening the track, without taking the aircraft off its procedure and with almost no workload for the pilot. ICA 100-37 presents it in exactly those terms: speed control is used "in order to facilitate sequencing or to reduce the need for vectoring"1.

Speed control has two limits. It acts slowly: it takes time and distance to have an effect, especially at high levels and with the aircraft clean2. And it costs fuel if kept for a long time3. That is why it works best early, while the aircraft is still far away.

General rules

Rule Source
The speed control remains in force until explicitly cancelled or amended by the controller. 4
Cancelling the speed control does not release the aircraft from the speed limits of the airspace class, such as 250 kt IAS below FL 100. 4
Speed control is not applied to aircraft entering or established in a holding pattern. 5
Speed control should be limited to what is necessary to establish or maintain separation or spacing. Avoid frequent changes, especially alternating increases and reductions. 6
If the pilot is unable to comply, the pilot says so, and you apply another method. 7
The pilot keeps the speed within ±10 kt or ±0.02 Mach. 8
Express speed in multiples of 10 kt IAS. At or above FL 250, you may use multiples of 0.01 Mach. 9
Tell the aircraft when the speed control is no longer required. 10

The speed limits for each airspace class are in the Airspace and ATS Services Manual.

Limits on arrival

An arriving aircraft may be instructed to maintain its maximum speed, minimum clean speed, minimum speed or a specified speed11. "Minimum clean speed" is the lowest speed possible without flaps, speed brakes or landing gear.

Phase Limit Source
Initial descent from cruising level, turbojet Below 250 kt IAS only with the crew's agreement 12
Below FL 150, turbojet Reductions down to 220 kt IAS, which is usually the minimum clean speed 13
Intermediate and final approach phases Only small changes, of up to ±20 kt IAS 14
From 4 NM from the threshold No speed control 15

Let the aircraft operate clean for as long as possible13. The crew normally stabilizes the approach (speed and configuration) at about 3 NM from the threshold15, so speed instructions must end before that.

Descending and slowing down do not mix

Avoid asking at the same time for a high rate of descent and a speed reduction. The aircraft is normally unable to do both, and a significant reduction during descent may require it to level off temporarily16. For the same reason, avoid applying horizontal and vertical speed control at the same time to the same flight17.

Speed restrictions published on SIDs and STARs remain in force unless you explicitly cancel or amend them18. Some of them exist because of RNAV navigation requirements, such as the maximum speed on a radius-to-fix (RF) leg.

Method

Who to adjust first

To open the spacing between successive aircraft, slow down the one behind first, or speed up the one ahead. Then adjust the others, in order19. Slowing down the one ahead first compresses the whole line.

IAS, TAS and compression during descent

The instructed speed is the indicated airspeed (IAS). What separates aircraft is the true airspeed (TAS) or, more precisely, the ground speed. At a constant IAS, TAS decreases as the aircraft descends20.

The consequence: two aircraft descending at the same IAS, with the one ahead lower, close in on each other, because the one ahead has a lower TAS. To keep the distance, the one ahead must fly a higher IAS. A rule of thumb is 6 kt IAS for every 1,000 ft of difference in height. Below FL 080, the difference between IAS and TAS is negligible for this calculation20.

Example

Aircraft A is descending through 6,000 ft. Aircraft B, right behind, is passing 11,000 ft. That is a 5,000 ft difference, or about 30 kt. For the distance between them not to decrease, A must fly about 30 kt IAS faster than B. For example, A at 250 kt and B at 220 kt.

Reference speeds

Good practice

Standardized speeds simplify the sequence: if all aircraft on the same segment fly the same speed, the spacing between them is maintained. A common scale for jets is:

Position Speed
Initial descent and long downwind 250 kt
Short downwind and base 210 to 220 kt
Intercept vector 180 kt
Final, until 4 NM from the threshold 160 kt

Turboprops and light aircraft fly slower. Confirm that the requested speed is possible for the type, especially on final.

Vertical speed control

The controller may also adjust the rate of climb or descent, to establish or maintain vertical separation between two climbing or two descending aircraft21. The rules follow the same logic as horizontal speed control: only what is necessary, without frequent changes, with notice when the restriction no longer applies, and with an alternative method ready in case the aircraft is unable to comply22.

The aircraft may be instructed to maintain a specific rate, a rate equal to or greater than a value, or a rate equal to or less than a value23. Before applying it, check down to which level the aircraft can maintain the requested rate24.

PT MMH, perform rate of descent 1,500 feet per minute.

TAM 3932, maximum rate of descent 2,000 feet per minute.

Phraseology

Portuguese English
TAM 3081, mantenha presente velocidade. TAM 3081, maintain present speed.
PT JRS, reduza velocidade em 20 nós. PT JRS, reduce speed by 20 knots.
PT FTA, reduza velocidade para 320 nós. Não sendo possível, informe. PT FTA, reduce speed to 320 knots. If unable advise.
FAB 2129, desça para FL 100, ao atingir reduza velocidade para 250 nós. FAB 2129, descend to FL 100, when reaching reduce speed to 250 knots.
PT LLT, mantenha 300 nós até Caxias. PT LLT, maintain 300 knots until Caxias.
PT LAN, não ultrapasse 300 nós. PT LAN, do not exceed 300 knots.
GLO 1799, reduza para velocidade mínima limpa. GLO 1799, reduce to minimum clean speed.
TAM 3730, reduza para velocidade de aproximação. TAM 3730, reduce to approach speed.
PT LLT, reassuma velocidade normal. PT LLT, resume normal speed.
PT MMH, sem restrições de velocidade. PT MMH, no speed restrictions.

Source: MCA 100-1625.

  1. ICA 100-37, Art. 975. See ICA 100-37. ↩

  2. ICA 100-37, Art. 235, § 5°, and Art. 232, § 3°. ↩

  3. ICA 100-37, Art. 226, § 2°. ↩

  4. ICA 100-37, Art. 227 and sole paragraph. ↩↩

  5. ICA 100-37, Art. 228. ↩

  6. ICA 100-37, Art. 229 and sole paragraph. ↩

  7. ICA 100-37, Art. 230 and sole paragraph. ↩

  8. ICA 100-37, Art. 231. ↩

  9. ICA 100-37, Art. 232 and § 1°. ↩

  10. ICA 100-37, Art. 233. ↩

  11. ICA 100-37, Art. 237 and sole paragraph. ↩

  12. ICA 100-37, Art. 238. ↩

  13. ICA 100-37, Art. 240 and sole paragraph. ↩↩

  14. ICA 100-37, Art. 241. ↩

  15. ICA 100-37, Art. 242 and sole paragraph. ↩↩

  16. ICA 100-37, Art. 239 and sole paragraph. ↩

  17. ICA 100-37, Art. 252. ↩

  18. ICA 100-37, Art. 243 and sole paragraph. ↩

  19. ICA 100-37, Art. 234. ↩

  20. ICA 100-37, Art. 235, §§ 1° to 4°. ↩↩

  21. ICA 100-37, Art. 244 and sole paragraph. ↩

  22. ICA 100-37, Arts. 245 to 247. ↩

  23. ICA 100-37, Arts. 248 to 250. ↩

  24. ICA 100-37, Art. 251. ↩

  25. MCA 100-16, Arts. 117 and 167. See MCA 100-16. ↩