Isavia ANS ehf., Reykjavíkurflugvelli, 102 Reykjavík /
Isavia ANS, Reykjavik Airport, IS-102 Reykjavik, Iceland
Sími / Telephone: + 354 424 4000 

AIC A 016 / 2019
Effective from  16 AUG 2019
Published on 16 AUG 2019
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Operations Without an Assigned Fixed Speed (OWAFS)

Content Responsibility: ISAVIA ANS

1 Introduction

1.1. The ICAO North Atlantic Region (NAT) is initiating a coordinated project to allow the use of flexible speeds in the NAT in accordance with ICAO rules. The implementation of Operations Without an Assigned Fixed Speed (OWAFS) is intended to enhance operator fuel and time efficiencies and reduce greenhouse gas (GHG) emissions.

The purpose of this AIC is to explain the implementation of this project within the Reykjavik Control Area.

1.2. The requirement to issue an assigned fixed Mach to all flights has been removed from NAT documents (ICAO Doc 7030), however, due to the technical design of the ACARS Oceanic Clearance (CLX) message, nearly all oceanic clearances issued to turbojet aircraft in the NAT Region will need to continue including an assigned Mach. If any variation to the assigned Mach is desired, flight crews must request such changes from ATC.

1.3. Aircraft manufacturers recommend a variable cruise Mach operation for maximum efficiency. Thus, ATC will assume that most flights will prefer to operate in the NAT region without a fixed Mach speed.

1.4. The following is an explanation of the terms "should", "must" and "shall" as used in this information letter.

  1. "Should" is used to indicate a recommended practice or policy that is considered as desirable for the safety of operations.
  2. "Shall" and "must" are used to indicate a practice or policy that is considered as necessary for the safety of operations.

2 Overview

2.1. All aircraft, regardless of FANS equipage, will be eligible for the application of OWAFS in both ATS surveillance and non-surveillance airspace.

2.2. Current ACARS / Voice oceanic clearance procedures will be retained.

2.3. Oceanic clearance procedures will remain unchanged. A fixed Mach will continue to be part of the oceanic clearance.

2.4. ANSPs will strive to remove a speed restriction when operationally feasible.

2.5. There will be two modes of operation regarding speed:

  1. Clearance with an assigned speed
  2. No speed assignment-provisions of ICAO Annex 2 (paragraph apply)

2.6. ATC will apply "speed control" as needed in accordance with guidance in ICAO Doc 4444.

2.7. The terms Cost Index or ECON should not normally be used in communications between ATC and aircraft with respect to the authorization for or use of OWAFS.

2.8. Implementation of OWAFS will, where possible, make use of existing CPDLC message sets and/or standard voice phraseology.

2.9. The following common phraseology, between ATC and flight crew, will be implemented across the NAT:

  1. To clear aircraft on a fixed speed:
    1. Voice: MAINTAIN MACH (speed)
    2.  CPDLC: SPDU-4/UM106: MAINTAIN (speed)
    3. ACARS data link oceanic clearance: Assigned Mach speed is required in oceanic CLX messages
  2. To remove the speed restriction:
  3. Response to a pilot inquiry:
    2. CPDLC SPDU-14/UM169 (free text): NO SPEED RESTRICTION

2.10. If an aircraft has been cleared on a fixed Mach speed;

  1. The flight crew will not need to request OWAFS, ATC will offer a variable Mach when possible.
  2. The flight crew abides by ICAO Annex 2 (paragraph b)
    Deviation from ATC assigned Mach number/indicated airspeed: the appropriate air traffic services unit shall be informed immediately.

2.11. If the aircraft then receives RESUME NORMAL SPEED (via CPDLC or Voice), the flight crew no longer needs to comply with a previously issued Mach. However, the flight crew shall advise ATC if, as the result of the RESUME NORMAL SPEED message, they intend to adjust their speed by plus or minus Mach 0.02 or more from their last assigned speed.

2.12. OWAFS will be offered to aircraft whenever the opportunity exists.

2.13. OWAFS will be managed in a manner dictated by required separation standards and safety of operations.

3 OWAFS operational scenario

3.1. Pre-Oceanic Entry:

  1. Airline operator files a flight plan for flight number AB123 with a NAT crossing speed of M.81.
  2. Prior to the oceanic entry point (OEP), AB123 requests an oceanic clearance with a speed of M.81.

3.2. Established in Oceanic Airspace:

  1. ATC controlling AB123 assesses the traffic situation with other aircraft.
  2. If the required minimum is sufficiently ensured:
    1. For CPLDC equipped aircraft an uplink message SPDU-13/UM116 RESUME NORMAL SPEED will be sent
    2. For aircraft without CPDLC capability, a voice message RESUME NORMAL SPEED will be sent;
  3. The flight crew no longer needs to comply with a previously issued Mach. However, the flight crew shall advise ATC if, as the result of the RESUME NORMAL SPEED message, they intend to adjust their speed by plus or minus Mach 0.02 or more from their last assigned speed. In this case, with a previously assigned speed of .81, they must inform ATC if the flight either slows to M.79 or less or speeds up to M.83 or more.
  4. ATC monitors AB123's progress, and its separation from other aircraft, in accordance with normal operating procedures.


  1. ATC coordinates with the receiving ANSP in accordance with inter-unit agreements.
  2. Upon arrival at the new OCA boundary, AB123 continues to operate without assigned speed.
  3. As a result of a change in the tactical situation, and OWAFS can no longer be offered, AB123 receives a CPDLC uplink SPDU-4 (UM106) MAINTAIN (speed - in this case M.81), or the equivalent clearance by voice, signifying a cessation of OWAFS due to conflicts. 
  4. Following resolution of conflicts, ATC again applies the procedures described before, allowing the flight crew to resume normal speed.

4 Flight Crew Training

4.1. Appropriate flight crew education will be required to ensure a thorough understanding of OWAFS procedures especially regarding responses to standard voice or CPDLC messages relating to speed assignments.

5 Contingency procedures

5.1. Advise ATC immediately of any data link issues that might affect FANS (CPDLC/ADS-C) data link operations or any situation, like weather conditions, that require a more significant speed change.

6 Special emphasis items

Operator attention is directed to the list below which provides a "quick reference" for OWAFS. It is intended to be used as a job aid for operators developing pilot training material.

Flight Crew:

  • Should ensure a FANS (CPDLC/ADS-C) connection with the appropriate oceanic control area;
  • Can request RESUME NORMAL SPEED via CPDLC (if not offered);
  • Should insert the appropriate current flight plan "cost index" (ECON) into the FMS. This should typically be within +/- .01 Mach of the assigned Mach;
  • Must inform ATC via CPDLC or voice if, as a result of the RESUME NORMAL SPEED message and subsequent insertion of cost index (ECON), the speed varies plus or minus Mach 0.02 or more from the assigned Mach; and
  • ATC will assign a fixed Mach if variable Mach can no longer be supported.

RESUME NORMAL SPEEDInstruction to resume a normal speed. The aircraft no longer needs to comply with a previously issued speed restrictionAllows for the use of cost index to produce a variable Mach. Fixed Mach is no longer requiredInsert the appropriate cost index into the FMC that should typically produce a Mach within +/- .01 Mach of the assigned Mach
MAINTAIN [SPEED]Instruction to maintain the specified speedAn assigned speed is required for traffic separationInsert the assigned Mach into the FMC and comply with the instruction

7 Implementation

The procedures described in this AIC are estimated to be implemented in the Reykjavik Control Area in October - November 2019 time frame. An exact implementation date will be published via a NOTAM.

It should be noted that implementation of those new procedures may not occur simultaneously within all NAT oceanic control areas. Aircraft operators are advised to consult AICs and NOTAMs for other NAT control areas.

8 Contacts

For further information and comment please contact:

Netfang / Email:

9 Website

The ICAO EUR/NAT Office Website is at: . Click on EUR & NAT Documents >> NAT Documents to obtain NAT Operations and NAT Region Update Bulletins and related project planning documents.



AIC hereby cancelled:  



NOTAM incorporated in this AIC: