Aerodrome Obstacle Chart – In-Depth Glossary

Definition and Purpose

An Aerodrome Obstacle Chart is a specialized aeronautical chart that visually and numerically presents the location, elevation, and characteristics of obstacles—both natural and man-made—around an aerodrome. Its primary function is to support safe aircraft operations during critical phases like take-off, approach, and landing by clearly depicting potential hazards in the aerodrome’s airspace. Developed in accordance with International Civil Aviation Organization (ICAO) and national aviation authority standards, these charts ensure global consistency and reliability.

Aerodrome Obstacle Charts are essential for the design and maintenance of safe instrument and visual flight procedures, supporting both routine and contingency operations. Flight procedure designers use them to identify controlling obstacles that determine minimum safe altitudes and necessary climb gradients. Aerodrome operators monitor compliance with Obstacle Limitation Surfaces (OLS), which are three-dimensional surfaces designed to protect aircraft from terrain and structures. Regulatory authorities use obstacle charts to assess aerodrome certification, compliance, and ongoing airspace management.

Key data on an Aerodrome Obstacle Chart includes:

• Obstacle position (latitude and longitude)
• Elevation (above mean sea level)
• Type (buildings, masts, cranes, trees, etc.)
• Marking/lighting status

This information, referenced to standardized geodetic datums (WGS-84 or NAD 83), is critical for instrument flight procedure (IFP) design, aerodrome expansion assessments, and managing obstacle reporting and marking requirements.

Aerodrome Obstacle Charts are indispensable pre-flight planning tools for pilots, directly influencing decisions on take-off run, approach paths, and minimum safe altitudes. Air traffic controllers use them to manage departures and arrivals, ensuring safe obstacle clearance. Modern digital obstacle charts further enhance utility for advanced airspace management and performance-based navigation (PBN).

Regulatory Standards

Aerodrome Obstacle Charts are governed by a hierarchy of international, regional, and national regulations.

International Standards

• ICAO Annex 4 – Aeronautical Charts: Prescribes content, symbology, accuracy, and update requirements.
• Annex 14 – Aerodromes: Defines Obstacle Limitation Surfaces (OLS).
• Annex 15 – Aeronautical Information Services: Regulates obstacle/terrain data provision.
• ICAO Doc 8697 – Aeronautical Chart Manual: Offers guidance on chart management and data exchange.

Regional and National Standards

• EUROCONTROL Terrain and Obstacle Data Manual: Sets digital data quality and delivery standards for Europe.
• FAA AC 150/5300-18A: Details survey, geodetic control, and chart production in the U.S.
• Aeronautical Information Publications (AIP): Each state may include specific charting requirements and local adaptations.

Regulatory processes ensure current and accurate obstacle information, with urgent updates disseminated via NOTAMs. Digital data standards enable seamless exchange and interoperability across agencies and borders.

Chart Types

Aerodrome Obstacle Charts come in several types, each serving specific operational or regulatory needs.

ICAO Type A (Operating Limitations)

• Focus: Take-off performance calculations
• Coverage: Take-off flight path area, declared distances, obstacle clearance surfaces
• Use: Pilots, flight planners, procedure designers

ICAO Type B

• Focus: Obstacles affecting approach, missed approach, and departure procedures
• Coverage: Up to 45 km from Aerodrome Reference Point (ARP)
• Use: Instrument procedure design, airspace management

Electronic/Advanced Types

• Digital formats (AIXM, XML) for integration with avionics, procedure design, and digital NOTAMs.

National Variants

• Some states may define additional types (Type C, heliport obstacle charts, military variants) to address unique operational contexts.

Data Requirements

The reliability of Aerodrome Obstacle Charts depends on the accuracy, completeness, and currency of their data.

Obstacle Data Attributes

• Geographic location (lat/long, WGS-84/NAD 83)
• Elevation above mean sea level (MSL)
• Type and dimensions
• Marking/lighting status
• Identifier/description
• Permanence/mobility (e.g., temporary cranes)

Coverage Areas

• Take-off flight path areas (runway ends and adjacent zones)
• Approach/missed approach corridors
• Within Obstacle Limitation Surfaces (OLS)
• PANS-OPS surfaces for instrument procedures

Accuracy and Resolution

• ICAO/FAA require horizontal accuracy within 1.0 m and vertical accuracy within 0.25 m for significant obstacles.

Survey Methods

• High-accuracy GNSS
• Aerial photogrammetry and LiDAR
• Spirit leveling for elevations
• Data validation and quality control before publication

Obstacle Limitation Surfaces (OLS)

Obstacle Limitation Surfaces (OLS) are three-dimensional geometric boundaries established to protect aircraft during ground and air movements around an aerodrome. Any object exceeding these surfaces is classified as an obstacle, requiring assessment, marking, and possible mitigation.

Common OLS types:

• Outer Horizontal Surface: Upper height limit for wide area
• Conical Surface: Sloped surface above the inner horizontal surface
• Inner Horizontal Surface: Protects aircraft in immediate aerodrome vicinity
• Approach Surface: Protects the landing approach path
• Transitional Surface: Flanks runway and approach surfaces
• Take-off Climb Surface: Ensures a clear departure path

Each OLS is dimensioned based on runway code, aerodrome reference code, and operational use. Obstacles are assessed for penetration and managed accordingly.

Typical OLS Profile (PDF)

Survey and Documentation Procedures

Aerodrome obstacle surveys and charting follow international and national technical standards.

1. Establish geodetic control (WGS-84/NAD 83)
2. Field survey using GNSS, photogrammetry, LiDAR, or leveling
3. Data processing for accuracy, conversion, and validation
4. Obstacle assessment against OLS and PANS-OPS surfaces
5. Chart compilation in prescribed ICAO format (plan/profile views, tables)
6. Review and approval by technical/regulatory authorities
7. Publication via AIP, digital platforms, or electronic charting

Operational Use

Aerodrome Obstacle Charts are used by:

• Procedure Designers: Identify controlling obstacles for flight procedure design (take-off, approach, missed approach).
• Aerodrome Operators: Monitor for OLS compliance, manage obstacle marking/lighting, and plan development.
• Pilots/Flight Planners: Pre-flight planning, hazard identification, and performance calculations.
• Regulators: Certification, audits, and compliance monitoring.
• Developers/Engineers: Evaluate new construction or modifications against OLS.

Examples:

• A designer uses a Type A chart to confirm a mast as the controlling obstacle for RWY 25 departures.
• Operators update charts and issue NOTAMs for temporary cranes or new structures.
• Developers check proposed building heights against OLS before construction.

Chart Attributes and Typical Content

A standard Aerodrome Obstacle Chart includes:

• Aerodrome Reference Point (ARP): Coordinates for chart orientation
• Runway/Stopway Details: Identification, dimensions, threshold coordinates
• Obstacle Table: Lists obstacles with ID, type, lat/long, elevation (MSL), height (AGL), distance, marking/lighting, notes
• Graphical OLS depiction: Plan/profile views showing obstacles relative to OLS and runways
• Magnetic variation
• Scale and grid: Typically 1:10,000 or 1:15,000, WGS-84 datum
• Datum and units: WGS-84 (global), NAD 83 (North America); feet/meters above MSL

Example Obstacle Table Format

Conclusion

Aerodrome Obstacle Charts are critical for safeguarding flight operations near airports. By systematically documenting and displaying all significant obstacles, these charts support safe procedure design, regulatory compliance, and operational efficiency in civil and military aviation worldwide.

For detailed regulatory references, see:

• ICAO Annex 4: Aeronautical Charts
• FAA AC 150/5300-18B: Survey and Data Collection
• EUROCONTROL - Terrain and Obstacle Data Manual