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9. Traffic Flow & Sequencing

9.1 Flow Management Tools

Flow Managers may issue Miles-in-Trail (MIT) or Minutes-in-Trail (MINIT) restrictions via the European Collaboration & Flow Management Project (ECFMP) to manage enroute spacing and regulate demand into constrained airspace or TMAs.

  • MIT: Requires aircraft to be spaced by a specified number of nautical miles at a designated fix or along a common airway.
  • MINIT: Specifies a minimum time interval between aircraft crossing a fix, commonly used when longitudinal separation is time-based, especially in procedural or non-radar environments.

Controllers shall ensure compliance with any ECFMP-issued flow restrictions and coordinate adjustments with adjacent sectors or FIRs when necessary. These restrictions may be supported by speed control or tactical rerouting as needed to maintain orderly flow.

9.2 Holding Procedures

Enroute holding may be used for traffic metering, weather delays, or coordination issues. Controllers should:

  • Assign published holding fixes or define ad-hoc holding patterns with clear instructions.
  • Include direction, fix, inbound leg length (1 or 1.5 minutes), and EFC (Expect Further Clearance) time.
  • Monitor spacing within the hold and adjust entries or exit order as required.
  • Coordinate holding instructions with adjacent sectors if aircraft may enter their airspace while holding.

Use of holding should be minimized where possible to reduce pilot and controller workload.

There are currently no published enroute holding fixes within the Muscat FIR. Most holding procedures are established within the Muscat and Salalah TMAs to support arrival sequencing and terminal area operations.

9.3 STAR Assignment & Expectations

Enroute controllers are responsible for assigning STARs (Standard Terminal Arrival Routes) when applicable, particularly during periods of high traffic volume or when coordination with TMA sectors requires early sequencing. STAR assignment should align with the expected runway and traffic flow for the destination aerodrome.

Controllers shall ensure that the assigned STAR is appropriate for the aircraft's routing and performance. Pilots should be informed to expect the assigned STAR, and any changes coordinated with approach or TMA controllers should be communicated promptly.

Where STARs are not assigned, aircraft may be expected to receive arrival routing from the TMA controller closer to destination.

9.4 Vertical & Speed Control Techniques

Controllers may apply speed control and/or vertical speed control to manage aircraft spacing and sequencing within enroute airspace. However, care must be taken to consider aircraft performance and energy management limitations when issuing such instructions.

9.4.1 Speed Control

Airspeed instructions (e.g., “Maintain 280 knots”) may be issued to achieve longitudinal spacing or flow regulation. However, speed control must be coordinated with vertical maneuvering to ensure feasibility.

9.4.2 Vertical Speed Control

Controllers may instruct aircraft to maintain a specific rate of climb or descent (e.g., “Descend at 2,000 feet per minute or greater”) to expedite level changes or achieve vertical separation. These instructions must remain within reasonable performance limits and should not conflict with other clearances.

9.4.3 Energy Management Considerations

Controllers shall avoid issuing conflicting instructions that may compromise aircraft performance. For example:

  • Instructing an aircraft to expedite climb while maintaining high speed is generally unfeasible, as aircraft typically require lower speeds to achieve a higher rate of climb.
  • Likewise, directing a steep descent rate while simultaneously requesting a low airspeed can be contradictory, since aircraft naturally gain speed during descent.

All climb/descent and speed instructions must be issued with an understanding of the aircraft’s energy state, type, and phase of flight to ensure safe and practical compliance.

9.5 Merging and Sequencing Traffic for TMA Entry

Controllers must ensure orderly traffic flows into TMAs (Terminal Manoeuvring Areas):

  • Establish appropriate in-trail spacing prior to TMA boundary (e.g., 10–15 NM depending on the Terminal SOP).
  • Use vectoring, speed control, or strategic routing to merge streams from different airways.
  • Coordinate sequencing strategies with TMA or approach sectors when multiple flows converge.

Ensure that aircraft handed over to the TMA controller are properly sequenced, levelled, and compliant with STAR or RNAV transitions.

9.6 Deconfliction of Crossing Routes

When managing traffic on intersecting or converging routes, controllers shall:

  • Apply lateral, vertical, or longitudinal separation to prevent conflicts at crossing points.
  • Assign strategic altitudes or use time-based spacing to deconflict paths.
  • Prioritize aircraft with right-of-way or time-sensitive trajectories when sequencing at busy intersections.
  • Consider potential wake turbulence implications when aircraft types differ significantly.

Deconfliction planning should begin well before the crossing fix, especially in high-density or non-radar areas.