Instrument Approach: Approach Procedure Using Navigation Instruments in Aviation

Definition

An Instrument Approach Procedure (IAP) is a published, standardized set of maneuvers performed using aircraft navigation instruments, guiding a flight safely from the en-route phase to landing or to a missed approach point—particularly when visual references are unavailable due to clouds, fog, precipitation, or darkness. Developed according to strict international (ICAO) or national (FAA) criteria, IAPs assure separation from terrain and obstacles, providing protected paths for descent, approach, and, if necessary, safe transition to holding or alternate routes.

Instrument approaches are essential for all-weather operations, underpinning safety and operational efficiency at airports large and small. They are designed to accommodate a wide range of aircraft and are a fundamental component of Instrument Flight Rules (IFR) operations worldwide.

Context and Purpose

Instrument approaches enable flight operations in Instrument Meteorological Conditions (IMC), when pilots cannot rely on visual cues to navigate or land. Their primary purposes are:

• Safety: Guarantee obstacle clearance and terrain avoidance, providing a protected, predictable descent path to the runway.
• Operational Continuity: Allow airports to remain accessible during adverse weather, supporting reliable schedules and reducing diversions.
• Traffic Management: Standardize arrival flows, aiding air traffic controllers in sequencing and separating arriving aircraft efficiently.
• Regulatory Compliance: Under IFR, pilots are legally required to use published IAPs when weather is below visual minimums.

Without instrument approaches, air travel would be far less reliable, particularly in regions with frequent low visibility or at night. Both commercial airlines and general aviation rely on IAPs to maximize the utility of airport infrastructure and maintain high safety standards.

Structure of an Instrument Approach Procedure

IAPs are divided into distinct segments, each with specific navigational and operational requirements:

Each segment is carefully designed to assure obstacle clearance, airspace protection, and operational feasibility for the types of aircraft expected to use the procedure.

Instrument Approach Chart Elements

Instrument approaches are published on approach plates (charts) which contain standardized, comprehensive information:

• Pilot Briefing Strip: Procedure name, airport, frequencies, approach course, elevations, missed approach instructions, and notes.
• Plan View: Overhead depiction of fixes, navigational aids, approach path, holding patterns, and significant obstacles/terrain.
• Profile View: Side-on cross-section showing descent path, altitude restrictions, step-down fixes, and the missed approach point.
• Minimums Section: Lists minimum altitudes (DA, DH, or MDA) and required visibility for each category of approach.
• Airport Diagram: Runways, taxiways, lighting, and surface layout for post-landing operations.

Approach charts also indicate required equipment, procedural notes (“DME required,” “Not authorized at night”), and special local considerations.

Use and Execution in Aviation Operations

When Instrument Approaches Are Used

• IMC: Required when weather is below VFR minimums (e.g., less than 1,000 ft ceiling or 3 miles visibility).
• Training/Proficiency: Used in good weather for pilot training and proficiency checks.
• Busy Terminal Airspace: Standardizes arrival flows, even in visual conditions.
• All-Weather Operations: Enable landings in very low visibility at equipped airports (e.g., Category II/III ILS).

Pilot and Crew Procedures

1. Preflight Planning: Review weather, NOTAMs, and select suitable approach(es) for destination and alternates. Ensure all required equipment and qualifications are met.
2. In-Flight Preparation: Obtain latest ATIS/AWOS, brief the approach, set navigation and communications, and review missed approach instructions.
3. Execution: Fly each segment per the chart, monitoring position, altitude, and configuration. At minimums, decide to land or initiate missed approach if criteria are unmet.
4. After Landing or Missed Approach: Follow taxi instructions or execute the published missed approach, preparing for another approach or diversion as necessary.

Approach Briefing Methodology

A systematic approach briefing enhances crew coordination and safety. Elements of a typical briefing include:

1. State the Approach: Identify procedure and confirm correct chart.
2. Chart Currency: Verify publication date is current.
3. Frequencies: Set and verify all navigation/communication radios.
4. Approach Course: Confirm and set final approach course.
5. Minimums: State and set DA, DH, or MDA.
6. Procedural Notes: Review special equipment, restrictions, or local notes.
7. Step-Down Fixes: Brief all altitude constraints and fixes.
8. Missed Approach: Review and brief the published missed approach.
9. Runway Environment: Discuss lighting, length, and expected taxi routes.
10. Aircraft Configuration: Specify gear, flaps, speeds, and automation use.

This process should be completed before reaching the initial approach fix, allowing time for questions and last-minute changes.

Equipment and Performance Requirements

• Minimum Equipment: Aircraft must have working navigation receivers (VOR, ILS, GPS, etc.), two-way radios, and appropriate approach equipment as specified by the chart.
• Special Requirements: Some approaches require additional or specific equipment (e.g., DME, ADF, IFR GPS, radar). These are indicated in the procedure name or chart notes.
• Performance Requirements: For some approaches (e.g., RNAV/RNP), specific navigational performance (accuracy) is required and noted on the chart.

Types of Instrument Approaches

• Precision Approach (PA): Provides both lateral and vertical guidance (e.g., ILS, GLS, PAR). Allows lowest minimums, supporting landings in very low visibility (down to 50 ft AGL for Cat III).
• Non-Precision Approach (NPA): Provides lateral guidance only (e.g., VOR, NDB, LOC without glideslope, LNAV). Minimums are higher due to lack of vertical path.
• Approach with Vertical Guidance (APV): Provides both lateral and vertical guidance but does not meet all precision approach standards (e.g., RNAV (GPS) LPV, LNAV/VNAV).

Key Takeaways

• Instrument approaches are essential for safe, reliable aviation operations in poor visibility.
• They are standardized, published procedures designed to ensure obstacle clearance and efficient traffic flow.
• Pilots must be thoroughly familiar with the approach chart, equipment requirements, and briefing process.
• Proper execution of instrument approaches underpins the safety and accessibility of airports worldwide.

Instrument approaches are a foundation of modern flight operations, supporting everything from major airline hubs to remote general aviation fields—keeping aviation safe, efficient, and all-weather capable.