Non-Precision Approach (NPA): Instrument Approach with Lateral Guidance Only

Introduction

A Non-Precision Approach (NPA) is a foundational instrument flight procedure that allows aircraft to approach runways in low visibility conditions, relying solely on lateral navigation guidance. Unlike precision approaches (such as ILS), NPAs do not offer an electronic glideslope or any form of vertical guidance. Instead, pilots must descend using published step-down fixes and maintain a minimum descent altitude (MDA) until the runway is in sight. These approaches are essential for safe access to airports lacking precision landing aids or where such aids are temporarily unavailable.

Core Principles of Non-Precision Approach

A non-precision approach is defined by the absence of vertical guidance. It provides only lateral guidance, which means pilots must precisely track the intended course to the runway using information from ground-based or satellite navigation aids. Vertical navigation is managed by the pilot according to altimeter readings and predetermined step-down fixes.

Key features of NPAs:

• Only lateral guidance is provided.
• The approach ends at a Minimum Descent Altitude (MDA).
• A Missed Approach Point (MAP) is specified for go-around decisions.
• Visual reference to the runway is required to descend below MDA.

NPAs are regulated globally under ICAO Annex 10 and Doc 8168 (PANS-OPS), as well as regional standards such as FAA TERPS.

Minimum Descent Altitude (MDA)

MDA is the lowest altitude to which a pilot can descend on a non-precision approach without visual reference to the runway. It is a horizontal plane, not a geographic point, and must be maintained from the final approach fix (FAF) until reaching the MAP unless the required visual references are established sooner.

• Purpose: To guarantee obstacle clearance during the approach.
• Determination: Based on the highest obstacle in the approach area, with additional safety margins.
• Enforcement: Descending below MDA without the runway in sight is a regulatory violation and a leading cause of Controlled Flight Into Terrain (CFIT) incidents.

Missed Approach Point (MAP)

The MAP is a critical location on the final approach course where the pilot must decide to either continue to land (if visual references are established) or execute the missed approach procedure.

• Defined by: Navigational fix, DME distance, GPS waypoint, or elapsed time from the FAF.
• Action at MAP: If the runway is not in sight or safe landing is not possible, the published missed approach must be initiated immediately to assure obstacle clearance.

Visual Descent Point (VDP)

A Visual Descent Point (VDP) is a charted point on NPAs indicating where a continuous descent from MDA to the runway can safely begin, provided the required visual cues are visible. The VDP ensures a stabilized approach and helps avoid rushed or steep descents that can lead to unsafe landings.

• Depiction: Shown as a “V” on approach charts.
• Best Practice: If the runway is not in sight by the VDP, continue at MDA to MAP and prepare for a missed approach.

Lateral vs. Vertical Guidance

Lateral Guidance

Lateral guidance in NPAs is supplied by navigation aids such as:

• VOR: Tracks aircraft along a specific radial.
• NDB: Uses bearings from a non-directional beacon.
• Localizer (LOC): Provides precise course alignment, but no glidepath.
• RNAV/LNAV: Uses GPS or other area navigation systems.
• Radar vectors (ASR/SRA): Provided by air traffic control.

Pilots must monitor course deviation indicators (CDI/HSI) to stay aligned with the intended path.

Vertical Guidance

NPAs do not provide official vertical guidance. Pilots descend according to published altitudes and step-down fixes, leveling at the MDA until the MAP or until visual reference is established. Some RNAV approaches may offer an Advisory Vertical Descent Angle (VDA), but this is for situational awareness only and not considered official vertical guidance.

Instrument Approach Procedure (IAP) Structure

Every instrument approach procedure (IAP) consists of several segments:

1. Initial Segment: From enroute structure to the approach area.
2. Intermediate Segment: Positions the aircraft for final approach.
3. Final Segment: From FAF to MAP or runway.
4. Missed Approach Segment: Ensures safe climb away from the runway or approach area.

NPAs are a specialized subset of IAPs that lack vertical guidance, requiring precise altitude management by the pilot.

Required Visual References

Pilots can only descend below MDA when they have acquired one or more of the following visual cues:

• Runway threshold, markings, or lights
• Runway end identifier lights (REIL)
• Approach lighting systems (ALS)
• Visual or precision approach path indicators (VASI/PAPI)
• Touchdown zone or its markings/lights

If visual reference is not established at or before MAP, a missed approach must be executed.

Types of Non-Precision Approaches

VOR Approach

A VOR approach uses a VHF Omnidirectional Range ground station to provide lateral guidance. The procedure is depicted on approach charts with inbound courses, step-down fixes, MDA, and MAP. VOR approaches are robust and widely used but require the pilot to monitor for signal issues or terrain interference.

NDB Approach

An NDB approach uses a non-directional beacon and the aircraft’s automatic direction finder (ADF) to provide course information. These approaches are less precise and more susceptible to atmospheric disturbances, but remain in use at remote or less-equipped airports.

Localizer (LOC) Approach

A localizer approach leverages the localizer component of an ILS, offering precise lateral guidance but no glideslope. Localizer approaches are common at airports where the glideslope is unavailable or not installed.

Localizer Type Directional Aid (LDA)

An LDA approach is similar to a localizer but offset from the runway centerline, sometimes requiring a visual maneuver before landing. Some LDAs have an associated glidepath, but most are considered NPAs due to the offset.

Simplified Directional Facility (SDF)

An SDF approach provides lateral guidance with a wider course width and potentially slight offset from the runway. It is less precise than a localizer and found at airports with installation limitations.

Area Navigation (RNAV/LNAV) Approach

RNAV (LNAV) approaches use GPS or other area navigation systems for lateral guidance. LNAV minimums indicate no vertical guidance. These approaches are flexible and can be designed for airports without ground navaids.

Approach Surveillance Radar (ASR/SRA) Approach

ASR/SRA approaches provide lateral guidance via air traffic control radar vectors. The controller issues headings to align with the runway, and specifies when to descend and when the MAP is reached.

Flying a Non-Precision Approach: Step-by-Step

1. Brief the Approach: Review the approach chart, navigation sources, altitudes, step-down fixes, MDA, MAP, and missed approach instructions.
2. Configure Aircraft: Set up navigation radios and avionics. Confirm all equipment is operational and review NOTAMs.
3. Initial Approach: Fly published altitudes and courses to the FAF.
4. Final Approach: Begin descent at the FAF, complying with step-down fixes.
5. Level at MDA: Maintain MDA from the final step-down fix to MAP or until visual references are in sight.
6. MAP Decision: At MAP, land if visual references are available and a safe landing is possible; otherwise, execute the missed approach.
7. Missed Approach: Follow published procedure for climb, navigation, and communication with ATC.

Stabilized Approach and Continuous Descent Final Approach (CDFA)

Modern best practices encourage the use of stabilized approaches and CDFA techniques. This means descending at a constant rate and speed, avoiding “dive and drive” (abrupt descent and level-off at MDA), which can lead to unstable approaches and increased risk.

Some RNAV NPAs publish an advisory Vertical Descent Angle (VDA) to help pilots fly CDFA profiles, resulting in safer and more predictable landings.

Safety Considerations

• Strict adherence to published minimums and altitudes is vital.
• Descending below MDA without visual contact is a major risk.
• Accurate identification of MAP and step-down fixes is crucial.
• Pilots should be prepared for a missed approach if visual references are not in sight.

Regulatory Background

NPAs are governed by international standards (ICAO) and national regulations (FAA, EASA, etc.). Procedures are designed to ensure obstacle clearance and safe transitions from instrument to visual flight.

Training and Proficiency

Pilots must be proficient in interpreting approach charts, using various navigation aids, managing step-downs and MDA, and executing missed approaches. Regular training and simulator practice are essential for maintaining instrument approach proficiency, especially for NPAs.

Future of Non-Precision Approaches

With the expansion of satellite-based navigation (e.g., GPS, GNSS), many traditional NPAs (like NDB and VOR) are being phased out in favor of RNAV and approaches with vertical guidance (APV, such as LPV and LNAV/VNAV). However, NPAs remain a critical backup and are still widely used, especially at secondary or remote airports.

Summary Table: Key Elements of Non-Precision Approaches

Conclusion

Non-Precision Approaches are essential procedures in the world of instrument flight, enabling pilots to safely land at airports with limited navigation infrastructure or when precision systems are unavailable. Mastery of NPAs requires strong procedural discipline, situational awareness, and a thorough understanding of approach charts and navigation aids. As aviation technology advances, the principles underlying NPAs remain foundational to instrument approach operations and flight safety.

For more information, review authoritative sources such as:

• ICAO Doc 8168 (PANS-OPS)
• FAA Instrument Procedures Handbook (FAA-H-8083-16)
• EASA AMC/GM to Part-SPA
• Jeppesen and government approach charts

Related Terms

• Precision Approach
• Instrument Landing System (ILS)
• Area Navigation (RNAV)
• Decision Altitude (DA)
• Minimum Descent Altitude (MDA)
• Missed Approach Procedure

This glossary article is for educational purposes and reflects industry best practices and regulatory standards as of 2024.