The Approach Controller
Approach Sequencing and Speed Control
While the Tower (TWR) controller primarily focuses on departures, the Approach (APP) controller is responsible for managing arrivals, ensuring they are sequenced safely and efficiently. This involves preventing arrivals from being too close together (which could force a go-around due to an occupied runway) or too far apart (which could result in unnecessary airborne holding and increased fuel consumption).
Approach Sequencing
Sequencing can be managed using several key concepts:
- Separation: The minimum vertical or lateral distance required between two aircraft. This includes radar separation and wake turbulence separation, both of which are critical in approach operations.
- Spacing: The desired distance between aircraft on final approach, which depends on factors such as weather conditions, airport layout, traffic volume, and pilot proficiency.
- Compression: A phenomenon that occurs when a leading aircraft reduces speed on final approach while trailing aircraft continue at a higher speed, causing them to close the gap. Controllers must anticipate this effect and adjust spacing accordingly.
For example, if the required spacing on final approach is 7 NM, an additional 1 NM can be added to account for compression, aiming for 8 NM final spacing when no additional wake turbulence separation is required.
Factors Affecting Final Approach Spacing
The APP controller must consider several factors when determining final approach spacing:
- Airport Layout: The number of runways, their configurations, and operational capabilities.
- Runway Exit Design: High-speed exits allow aircraft to vacate the runway more quickly, reducing spacing requirements.
- Traffic Volume: Depending on demand, priority may be given to either arrivals or departures, requiring close coordination with TWR.
- Low Visibility Procedures (LVPs): Increased spacing is necessary during reduced visibility conditions.
- Ground Situational Awareness: Monitoring ground movements to adjust spacing for optimal traffic flow.
Speed Control for Approach Management
To establish and maintain proper spacing, controllers should first:
- Reduce the speed of trailing aircraft or
- Increase the speed of leading aircraft, then adjust the speeds of other aircraft accordingly.
Aircraft may be assigned specific speed instructions, such as:
- Maximum speed
- Minimum clean speed (minimum speed without flaps, speed brakes, or landing gear deployed)
- Minimum approach speed
- A specified IAS (Indicated Airspeed)
General Speed Control Guidelines
- Controllers should avoid instructing aircraft to reduce speed while maintaining a high descent rate, as these maneuvers are often incompatible.
- Aircraft should be allowed to remain in a clean configuration for as long as possible.
- Below FL150, turbojet aircraft should not be reduced to less than 220 knots IAS, which is close to their minimum clean speed.
- On intermediate and final approach, only minor speed adjustments (not exceeding ±20 knots IAS) should be used.
Standard Speed Reductions on Final Approach
The following speed recommendations ensure efficient sequencing and predictable spacing:
| Distance from Runway | Maximum IAS |
|---|---|
| 15 NM | 250 knots |
| 10 NM (Glideslope Intercept) | 200 knots |
| 7 NM | 190 knots |
| 6 NM | 180 knots |
| 5 NM | 170 knots |
| 4 NM | 160 knots |
- Pilots should not exceed 200 knots upon reaching the glideslope (approximately 10 NM out).
- The approach clearance does not cancel speed restrictions, unless explicitly stated by the controller.
- If unsure whether a pilot is aware of the speed restrictions, it is best to reissue them rather than assume the pilot will adjust preemptively.
- Assigning 180 knots to 6 NM can lead to less precise approaches, as different aircraft types decelerate at different rates. Using 170 knots to 5 NM or 160 knots to 4 NM provides more consistency, reducing spacing deviations to around 0.3–0.4 NM.
Best Practices for APP Controllers
- When workload increases, reduce aircraft speeds earlier to maintain control over sequencing.
- Avoid shortening aircraft paths too much, as this can disrupt the flow and spacing.
- Use standard speeds consistently to maintain an organized sequence.
- Prioritize situational awareness and proactive adjustments to prevent unnecessary go-arounds.
By applying these principles, an approach controller can effectively manage arrivals, ensuring safe and efficient sequencing while maintaining smooth coordination with Tower.