Approach Procedure
An Approach Procedure (AP) or Instrument Approach Procedure (IAP) is a structured series of maneuvers for IFR aircraft to transition from en-route to landing or...
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Aviation
Flight Operations
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Definition
Approach in aviation is the sequence of flight operations and the prescribed flight path that an aircraft follows when transitioning from the en route or terminal phase to the immediate vicinity of a runway to conduct a landing. This critical phase begins with descent planning and continues through the final approach and touchdown, incorporating both instrument and visual procedures. The approach is governed by international and national standards (e.g., ICAO Doc 8168 (PANS-OPS) , FAA Instrument Procedures Handbook , EASA Air OPS Regulation (EU) No 965/2012 ). Its purpose is to ensure that the aircraft is safely configured, aligned, and aerodynamically prepared to land, considering terrain, airspace, environmental factors, and traffic sequencing.
Approaches may be conducted under Instrument Meteorological Conditions (IMC) using published instrument approach procedures (IAPs), or under Visual Meteorological Conditions (VMC) as a visual approach, each requiring distinct operational, regulatory, and procedural compliance.
Where is it used?
The approach phase is universal and applies at all aerodromes, from small uncontrolled airfields to the busiest international airports. Instrument approaches are especially vital in poor visibility or challenging terrain, while visual approaches are common in favorable conditions.
How is it used?
Pilots and air traffic controllers coordinate closely, following published charts and procedures, standardized communications, configuration changes, and adherence to approach minima and missed approach points. The approach phase is critical for safe flight and requires strict compliance; improper execution can result in controlled flight into terrain (CFIT), loss of separation, runway excursions, or the need for a go-around.
Authoritative References:
Key Elements and Phases of the Approach Flight Path
The approach phase encompasses several critical sub-phases. Each has specific objectives and regulatory guidance to ensure a safe and efficient transition from cruise to landing.
1. Descent Planning
Descent planning involves determining the optimal point to begin descent from cruise altitude to the approach environment. This ensures a continuous, energy-efficient, and safe flight path to the runway.
Key Concepts:
- Top of Descent (TOD): Calculated based on altitude to lose, aircraft performance, and environmental factors. The rule of thumb: altitude to lose (in thousands of feet) × 3 = descent distance in nautical miles.
- Advanced Descent Planning: Modern aircraft use Flight Management Systems (FMS) to manage continuous descent approaches (CDA), improving fuel efficiency and reducing noise/emissions.
- ATC Involvement: In controlled airspace, ATC provides descent clearances, crossing restrictions, and speed assignments.
- Regulatory Criteria: ICAO Doc 8168 provides descent gradients and obstacle clearance criteria.
Operational Application:
Proper descent planning avoids high rates of descent, ensures stable approaches, and reduces the need for last-minute configuration or speed changes.
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2. Approach Setup and Briefing
Before initiating the approach, pilots conduct a systematic review and setup process to ensure alignment and readiness.
Key Elements:
- Approach Chart Review: Includes frequencies, altitudes, course, minima, missed approach procedures, and airport layout.
- Weather and NOTAM Assessment: Current and forecast conditions inform approach selection and configuration.
- Briefing Content: Type of approach, runway, minima, missed approach, configuration points, special hazards, crew roles, and communications.
- Checklist Integration: Ensures aircraft systems and navigation are properly configured.
Regulatory Requirements:
ICAO Annex 6 and EASA Air OPS require documented approach briefing procedures and defined multi-crew communication protocols.
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3. Initial Approach and Traffic Pattern Entry
This phase connects the arrival or STAR to the final approach, either via instrument procedures or by entering a visual traffic pattern.
Instrument Approach Procedures (IAPs):
- Initial Approach Fix (IAF): Entry point for the published approach.
- Arrival Routing: STARs and vectors guide the aircraft to the IAF.
- Transition to FAF: Via intermediate fixes with altitude and speed restrictions.
Visual Traffic Pattern (VFR):
- Pattern Entry: Typically on the downwind leg at published Traffic Pattern Altitude.
- Spacing and Sequencing: Pilots visually acquire traffic and self-announce intentions at uncontrolled airports.
Regulatory Guidance:
ICAO Doc 8168 and Doc 4444 specify initial approach segment criteria. FAA and EASA define pattern entry and communications.
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4. Configuration and Descent to Landing
Aircraft configuration involves systematic deployment of aerodynamic devices and system adjustments to safely prepare for landing.
Key Configuration Changes:
- Landing Gear: Extended per SOPs, typically on downwind or at a designated point.
- Flap Deployment: Extended in stages to increase lift and drag, allowing slower approach speeds.
- Approach Speed: Calculated based on weight, wind, and turbulence, with a gust factor added.
- Checklist Discipline: Descent, before landing, and landing checklists ensure all systems and configurations are correct.
Regulatory Guidance:
ICAO Doc 8168 and FAA AC 91-79A recommend configuration and energy management best practices, including the “stabilized approach window.”
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5. Stabilized Approach Criteria
A stabilized approach is one where the aircraft is on correct path, speed, and configuration, with minimal deviation. This is essential for safe landings and is mandated by major aviation authorities.
Stabilized Approach Gates:
| Altitude (AGL) | Conditions | Criteria |
|---|---|---|
| 1,000 ft | IMC | On course, on glide path, configured, target speed, checklists complete |
| 500 ft | VMC | Same as above; only minor corrections allowed below this point |
Stabilization Parameters:
- On centerline and glide path
- Within –5/+15 knots of target speed
- Engines above idle
- Sink rate not exceeding 1,000 fpm unless briefed
- Fully configured with checklists complete
Action if Not Stabilized:
A go-around is mandatory if criteria are not met at the gate altitude.
Regulatory Reference:
- ICAO Doc 8168
- FAA AC 120-71B
- EASA CAT.OP.MPA.300
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6. Final Approach Segment
The final approach extends from the Final Approach Fix (FAF) or Final Approach Point (FAP) to the runway threshold or missed approach point (MAP).
Types of Final Approach:
- Precision Approach: Lateral and vertical guidance (e.g., ILS).
- Non-Precision Approach: Lateral guidance only (e.g., VOR, NDB, LOC).
- Visual Approach: Visual reference to the runway and lighting systems.
Key Considerations:
- Maintain glide path (visual or instrument guidance)
- Manage airspeed and power precisely
- Avoid over/under-correcting for wind or configuration
Regulatory Requirement:
ICAO Doc 8168 prescribes obstacle clearance and missed approach protection.
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7. Landing – Roundout, Flare, Touchdown, and Rollout
This final sequence transitions the aircraft from approach to ground contact and deceleration.
Phases of Landing:
- Roundout: Initiated at 10–50 ft AGL, raises the nose and decreases descent rate.
- Flare: At 1–2 ft AGL, pitch increases further to ensure gentle touchdown.
- Touchdown: Main wheels contact runway, ideally in the touchdown zone.
- Rollout: Maintain directional control, apply braking and spoilers, manage crosswind with aileron input.
Special Techniques:
Crosswind, soft, and short field landings require specific adjustments.
Error Prevention:
Avoid excessive flare, correct for wind drift, and do not force the aircraft onto the ground.
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Operational Use and Examples
Airline and General Aviation
In airline operations, approaches are standardized, with company SOPs, regulatory oversight, and recurrent training. Flight management systems automate much of the process, but pilots remain responsible for monitoring and manual intervention when necessary.
General aviation relies on similar principles, though often with less automation and ATC support, making pilot proficiency in approach procedures and visual pattern work even more critical.
Visual vs. Instrument Approach Example
- Instrument Approach (e.g., ILS): Used in poor weather or at night. The pilot follows published procedures and navigational aids for a safe landing.
- Visual Approach: Used in good visibility. The pilot uses sight of the runway and visual cues to align and land.
Missed Approach/Go-Around
If the approach cannot be completed safely (unstable, obstacles, traffic, or runway not in sight by minima), the pilot must execute the missed approach or go-around procedure, as published and briefed.
Safety, Compliance, and Training
- Approach and landing accidents account for a significant portion of aviation incidents. Strict adherence to stabilized approach criteria and proper planning significantly reduces these risks (ICAO Doc 9859, Safety Management Manual ).
- Ongoing training in approach procedures, both in simulators and real-world flying, is essential for all pilots.
Summary
The approach phase is a cornerstone of safe flight operations, demanding rigorous planning, precise execution, and adherence to international standards. Whether under instrument or visual conditions, the approach encompasses descent planning, configuration, navigation, and communication, culminating in a safe landing or a well-executed go-around if conditions are not met.
For further details: