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 160 knots to 4 NM or 170 knots to 5 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.
Climb and Descent Clearances
ATC issues climb and descent clearances to facilitate departures, arrivals, or to help aircraft avoid adverse weather conditions. As a rule of thumb, controllers can estimate that an aircraft descends at approximately 300 feet per NM (or 1,000 feet per 3 NM), commonly referred to as the 3:1 rule.
For example, when guiding an aircraft over the downwind leg, it should be higher than 8,000 feet abeam the field; otherwise, it will be too high to turn onto a 10 NM final. To compensate for excessive altitude, pilots may adjust their descent rate at their discretion. However, controllers may assign a specific descent rate if necessary—but should act promptly, as even with speed brakes, an aircraft’s descent rate has its limits.
ATC can also manage vertical speed during both climb and descent to ensure separation between successive or crossing aircraft. This is particularly useful in high-traffic scenarios. In TopSky radar, the assigned rate of climb/descent (ARC function) is marked in the aircraft’s radar label.
When issuing an approach clearance, pilots are expected to descend to the published altitude for the approach. If the controller requires a different altitude, this must be explicitly stated.
Radar Vectoring
Radar vectoring is the process of guiding an aircraft using ATC-assigned headings instead of standard IFR procedures (SID/STAR/Instrument Approach). Controllers must adhere to the Minimum Vectoring Altitude (MVA), which ensures obstacle clearance while vectoring aircraft.
When issuing radar vectors, controllers must:
- Inform the pilot of the purpose of the vector and specify the limit of the vector (e.g., "Vectoring for ILS approach Runway 36").
- When terminating vectoring, instruct the pilot to resume own navigation.
- Maintain a minimum separation of 2.5 NM between aircraft to ensure at least 5 NM of radar separation. If at higher altitudes, separation must be increased accordingly.
- Avoid vectoring aircraft into uncontrolled airspace, except in emergencies or to circumvent severe weather.
- If an aircraft reports unreliable directional instruments, instruct the pilot to make all turns at an agreed rate and to comply with instructions immediately upon receipt.
Obstacle Clearance
When vectoring an IFR flight or issuing a direct routing that takes an aircraft off an ATS route, controllers must ensure that prescribed obstacle clearance is maintained at all times until the pilot resumes navigation. If necessary, the minimum vectoring altitude (MVA) must be adjusted for low-temperature corrections.
Radar vectors can be provided in two ways:
- Heading Assignment: e.g., "Turn left heading 180°."
-
Relative Turn Instruction: e.g., "Turn right by 10°."
- This should only be used when there is insufficient time to request a specific heading.
If a radar vector is not self-explanatory (e.g., for final approach), the reason should always be provided (e.g., "Turn left heading 180° for spacing").
Important Considerations:
- When an aircraft is already in a turn, avoid ambiguous instructions like "Turn left/right by..." since the aircraft may not know which heading this refers to. Instead, use "Stop turn" if an immediate heading correction is needed.
- For ILS or localizer approaches, vectoring should be within 30° of the final approach course.
- Example: Runway 36 → Heading 330° or 030° for intercept.