Speed Adjustments — AIM 4-4-12 Explained

AIM Text

ATC will issue speed adjustments to pilots of radar controlled aircraft to achieve or maintain appropriate spacing. If necessary, ATC will assign a speed when approving deviations or radar vectoring off procedures that include published speed restrictions or a chart note used to transition from Mach to IAS. If no speed is assigned, speed becomes pilot's discretion. However, when the aircraft reaches the end of the STAR, the last published speed on the STAR must be maintained until ATC deletes it, assigns a new speed, issues a vector, assigns a direct route, or issues an approach clearance.

NOTE-

A chart note identifying a speed to maintain after transitioning from Mach to IAS may be published in lieu of or in addition to other published speed restrictions on a STAR.

REFERENCE-

AIM, Para 5-4-1, Standard Terminal Arrival (STAR) Procedures
ATC will express all speed adjustments in terms of knots based on indicated airspeed (IAS) in 5 or 10 knot increments except that at or above FL 240 speeds may be expressed in terms of Mach numbers in 0.01 increments. The use of Mach numbers is restricted to aircraft with Mach meters.
Pilots complying with speed adjustments (published or assigned) are expected to maintain a speed within plus or minus 10 knots or 0.02 Mach number of the specified speed.
When ATC assigns speed adjustments, it will be in accordance with the following recommended minimums:
1. To aircraft operating between FL 280 and 10,000 feet, a speed not less than 250 knots or the equivalent Mach number.
  NOTE-
  1. On a standard day the Mach numbers equivalent to 250 knots CAS (subject to minor variations) are:
    FL 240-0.6
    FL 250-0.61
    FL 260-0.62
    FL 270-0.64
    FL 280-0.65
    FL 290-0.66.
  2. When an operational advantage will be realized, speeds lower than the recommended minima may be applied.
2. To arriving turbojet aircraft operating below 10,000 feet:
  1. A speed not less than 210 knots, except;
  2. Within 20 flying miles of the airport of intended landing, a speed not less than 170 knots.
3. To arriving reciprocating engine or turboprop aircraft within 20 flying miles of the runway threshold of the airport of intended landing, a speed not less than 150 knots.
4. To departing aircraft:
  1. Turbojet aircraft, a speed not less than 230 knots.
  2. Reciprocating engine aircraft, a speed not less than 150 knots.
When ATC combines a speed adjustment with a descent clearance, the sequence of delivery, with the word “then” between, indicates the expected order of execution.
EXAMPLE-
1. Descend and maintain (altitude); then, reduce speed to (speed).
2. Reduce speed to (speed); then, descend and maintain (altitude).
NOTE-

The maximum speeds below 10,000 feet as established in 14 CFR section 91.117 still apply. If there is any doubt concerning the manner in which such a clearance is to be executed, request clarification from ATC.
If ATC determines (before an approach clearance is issued) that it is no longer necessary to apply speed adjustment procedures, they will:
1. Advise the pilot to “resume normal speed.” Normal speed is used to terminate ATC assigned speed adjustments on segments where no published speed restrictions apply. It does not cancel published restrictions on upcoming procedures. This does not relieve the pilot of those speed restrictions which are applicable to 14 CFR section 91.117.
  
  EXAMPLE-
  
  (An aircraft is flying a SID with no published speed restrictions. ATC issues a speed adjustment and instructs the aircraft where the adjustment ends): “Maintain two two zero knots until BALTR then resume normal speed.”
  
  NOTE-
  The ATC assigned speed assignment of two two zero knots would apply until BALTR. The aircraft would then resume a normal operating speed while remaining in compliance with 14 CFR section 91.117.
2. Instruct pilots to “comply with speed restrictions” when the aircraft is joining or resuming a charted procedure or route with published speed restrictions.
  
  EXAMPLE-
  
  (ATC vectors an aircraft off of a SID to rejoin the procedure at a subsequent waypoint. When instructing the aircraft to resume the procedure, ATC also wants the aircraft to comply with the published procedure speed restrictions): “Resume the SALTY ONE departure. Comply with speed restrictions.”
  
  CAUTION-
  The phraseology “Descend via/Climb via SID” requires compliance with all altitude and/or speed restrictions depicted on the procedure.
3. Instruct the pilot to “resume published speed.” Resume published speed is issued to terminate a speed adjustment where speed restrictions are published on a charted procedure.
  
  NOTE-
  When instructed to “comply with speed restrictions” or to “resume published speed,” ATC anticipates pilots will begin adjusting speed the minimum distance necessary prior to a published speed restriction so as to cross the waypoint/fix at the published speed. Once at the published speed, ATC expects pilots will maintain the published speed until additional adjustment is required to comply with further published or ATC assigned speed restrictions or as required to ensure compliance with 14 CFR section 91.117.
  
  EXAMPLE-
  
  (An aircraft is flying a SID/STAR with published speed restrictions. ATC issues a speed adjustment and instructs the aircraft where the adjustment ends): “Maintain two two zero knots until BALTR then resume published speed.”
  
  NOTE-
  
  The ATC assigned speed assignment of two two zero knots would apply until BALTR. The aircraft would then comply with the published speed restrictions.
4. Advise the pilot to “delete speed restrictions” when either ATC assigned or published speed restrictions on a charted procedure are no longer required.
  
  EXAMPLE-
  
  (An aircraft is flying a SID with published speed restrictions designed to prevent aircraft overtake on departure. ATC determines there is no conflicting traffic and deletes the speed restriction): “Delete speed restrictions.”
  
  NOTE-
  When deleting published restrictions, ATC must ensure obstacle clearance until aircraft are established on a route where no published restrictions apply. This does not relieve the pilot of those speed restrictions which are applicable to 14 CFR section 91.117.
5. Instruct the pilot to “climb via” or “descend via.” A climb via or descend via clearance cancels any previously issued speed restrictions and, once established on the depicted departure or arrival, to climb or descend, and to meet all published or assigned altitude and/or speed restrictions.
  EXAMPLE-
  1. (An aircraft is flying a SID with published speed restrictions. ATC has issued a speed restriction of 250 knots for spacing. ATC determines that spacing between aircraft is adequate and desires the aircraft to comply with published restrictions): “United 436, Climb via SID.”
  2. (An aircraft is established on a STAR. ATC must slow an aircraft for the purposes of spacing and assigns it a speed of 280 knots. When spacing is adequate, ATC deletes the speed restriction and desires that the aircraft comply with all published restrictions on the STAR): “Gulfstream two three papa echo, descend via the TYLER One arrival.”
  NOTE-
  1. In example 1, when ATC issues a “Climb via SID” clearance, it deletes any previously issued speed and/or altitude restrictions. The pilot should then vertically navigate to comply with all speed and/or altitude restrictions published on the SID.
  2. In example 2, when ATC issues a “Descend via <STAR name> arrival,” ATC has canceled any previously issued speed and/or altitude restrictions. The pilot should vertically navigate to comply with all speed and/or altitude restrictions published on the STAR.
  CAUTION-
  When descending on a STAR, pilots should not speed up excessively beyond the previously issued speed. Otherwise, adequate spacing between aircraft descending on the STAR that was established by ATC with the previous restriction may be lost.
Approach clearances supersede any prior speed adjustment assignments, and pilots are expected to make their own speed adjustments as necessary to complete the approach. However, under certain circumstances, it may be necessary for ATC to issue further speed adjustments after approach clearance is issued to maintain separation between successive arrivals. Under such circumstances, previously issued speed adjustments will be restated if that speed is to be maintained or additional speed adjustments are requested. Speed adjustments should not be assigned inside the final approach fix on final or a point 5 miles from the runway, whichever is closer to the runway.
The pilots retain the prerogative of rejecting the application of speed adjustment by ATC if the minimum safe airspeed for any particular operation is greater than the speed adjustment.

NOTE-

In such cases, pilots are expected to advise ATC of the speed that will be used.
Pilots are reminded that they are responsible for rejecting the application of speed adjustment by ATC if, in their opinion, it will cause them to exceed the maximum indicated airspeed prescribed by 14 CFR section 91.117(a), (c) and (d). IN SUCH CASES, THE PILOT IS EXPECTED TO SO INFORM ATC. Pilots operating at or above 10,000 feet MSL who are issued speed adjustments which exceed 250 knots IAS and are subsequently cleared below 10,000 feet MSL are expected to comply with 14 CFR section 91.117(a).
Speed restrictions of 250 knots do not apply to U.S. registered aircraft operating beyond 12 nautical miles from the coastline within the U.S. Flight Information Region, in Class E airspace below 10,000 feet MSL. However, in airspace underlying a Class B airspace area designated for an airport, or in a VFR corridor designated through such as a Class B airspace area, pilots are expected to comply with the 200 knot speed limit specified in 14 CFR section 91.117(c).
For operations in a Class C and Class D surface area, ATC is authorized to request or approve a speed greater than the maximum indicated airspeeds prescribed for operation within that airspace (14 CFR section 91.117(b)).

NOTE-

Pilots are expected to comply with the maximum speed of 200 knots when operating beneath Class B airspace or in a Class B VFR corridor (14 CFR section 91.117(c) and (d)).
When in communications with the ARTCC or approach control facility, pilots should, as a good operating practice, state any ATC assigned speed restriction on initial radio contact associated with an ATC communications frequency change.

Source: FAA Aeronautical Information Manual · current edition · paragraph 4-4-12.

Research Notes

AIM 4-4-12 covers speed adjustments — ATC-issued speed restrictions and the pilot's response.

Common speed instructions:

"Reduce speed to [knots]": Slow to the specified KIAS
"Increase speed to [knots]": Speed up to the specified KIAS
"Maintain present speed": Don't change speed
"Maintain best forward speed": Highest sustainable speed for the aircraft (typically just below Vno)
"Reduce to minimum approach speed": Slow to your approach speed without making it dangerous

The 'unable' response: If the aircraft cannot achieve the requested speed (e.g., a Skylane being asked to maintain 170 KIAS in cruise — outside its envelope), say "unable" and state your achievable speed.

The 250-knot rule: Below 10,000 MSL, the speed limit is 250 KIAS per § 91.117(a). ATC may grant deviations but the pilot must explicitly request.

The 200-knot rule: Below 2,500 AGL within 4 NM of Class B/C/D primary airport, the limit is 200 KIAS per § 91.117(b).

Reference: § 91.117 (aircraft speed); AIM 4-4-12.

4-4-12. Speed Adjustments

AIM Text

Research Notes

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