eTOD (Electronic Terrain and Obstacle Data)
Electronic Terrain and Obstacle Data — digital terrain/obstacle datasets organised by Areas 1-4 with mandatory accuracy, integrity, and traceability for PBN, TAWS, procedure design, and charting
eTOD (Electronic Terrain and Obstacle Data)
Definition
Electronic Terrain and Obstacle Data (eTOD) is the collection of standardised digital data sets that represent the Earth's terrain surface and artificial or natural vertical obstacles above defined collection surfaces. The data sets are organised by four coverage Areas (1 through 4), each with defined data quality attributes: accuracy, resolution, integrity, traceability, and post-spacing. eTOD is published and exchanged under ICAO Annex 15 and PANS-AIM (Doc 10066).
The terrain data set is a continuous elevation grid representing the bare Earth (or first reflective surface) at regular post-spacings, referencing WGS-84 horizontally and mean sea level vertically. The obstacle data set captures the three-dimensional extent of fixed or mobile structures that penetrate defined collection surfaces. Obstacle data and terrain data are maintained as separate data sets; obstacles must not be included in terrain data sets.
eTOD is one of five mandatory digital data set types under Annex 15, Chapter 5. It is the foundational Digital AIM product serving terrain awareness in avionics and ground-based safety systems.
Regulatory Basis
Annex 15 (Aeronautical Information Services), Sixteenth Edition (2018), Chapter 5, Section 5.3.3, establishes the Standards and Recommended Practices for terrain and obstacle data sets. Coverage area definitions appear in §5.3.3.1. Terrain data Standards are in §5.3.3.3 and obstacle data Standards in §5.3.3.4. Annex 15 explicitly delegates the numerical requirements for accuracy, resolution, integrity, and post-spacing to PANS-AIM (Doc 10066), Appendices 1 and 8.
Doc 10066 (PANS-AIM, First Edition, 2018), Section 5.3.3.2 specifies the full content requirements for terrain and obstacle data sets. Appendix 1 (Aeronautical Data Catalogue), Tables A1-6 (obstacle) and A1-8 (terrain) carry per-Area numeric requirements. Appendix 6 lists mandatory and optional attributes for terrain (Table A6-1) and obstacle (Table A6-2) data. Appendix 8 provides graphical definitions of terrain and obstacle data collection surfaces for each Area.
The history of the eTOD SARPS is traceable to Amendment 33 of Annex 15 (Twelfth Edition, applicable 25 November 2004), which introduced electronic terrain and obstacle data provisions following recommendations of GNSSP/4, OCP/12, and OCP/13. The Sixteenth Edition consolidated the provisions after the AIS-to-AIM transition work of AIS-AIMSG culminating in Amendment 40 (2018).
Annex 6, Part I (Operation of Aircraft), §6.15 mandates that turbine aircraft above 5 700 kg or carrying more than nine passengers be equipped with a ground proximity warning system (GPWS) with forward- looking terrain avoidance (TAWS/eGPWS). Section §6.15.2 requires the operator to maintain current terrain and obstacle database management procedures, linking eTOD quality directly to airworthiness and operator compliance.
Operational Meaning
PANS-AIM §5.3.3.2 Note enumerates the intended air navigation applications for eTOD:
- Ground proximity warning system with forward-looking terrain avoidance (TAWS/eGPWS) and minimum safe altitude warning (MSAW).
- Contingency procedures for emergency during missed approach or take-off (drift-down analysis, emergency landing location).
- Aircraft operating limitations analysis.
- Instrument procedure design, including circling approaches.
- En-route drift-down and emergency landing location determination.
- Advanced surface movement guidance and control (A-SMGCS).
- Aeronautical chart production and onboard navigation databases.
Additional uses include flight simulators, synthetic vision systems, and obstacle height restriction or removal analysis.
eTOD is a prerequisite for performance-based navigation (PBN) minima calculation. PANS-OPS (Doc 8168) obstacle clearance methodology depends directly on the accuracy and coverage of Area 2 and Area 4 eTOD. Gaps or inaccuracies in State eTOD propagate into conservative obstacle clearance margins and elevated minima, restricting access.
For eGPWS and TAWS, the onboard terrain database is derived from the State eTOD dataset. Gap or inaccuracy in national eTOD directly reduces TAWS effectiveness for aircraft operating in that State's airspace.
Coverage Areas
Annex 15 §5.3.3.1 defines the four Areas as the fundamental organisational structure of eTOD:
Area 1 is the entire territory of a State. Terrain data is a mandatory Standard for all of Area 1. Obstacle data is mandatory for all obstacles whose height above ground is 100 m or higher.
Area 2 covers the vicinity of an aerodrome used regularly by international civil aviation, subdivided into four sub-areas:
- Area 2a — the runway strip plus any clearway. Mandatory Standard for terrain and obstacle data, with an obstacle collection surface 3 m above the nearest runway elevation at centreline.
- Area 2b — departure corridor extending 10 km from Area 2a with a 15 per cent splay each side; obstacle surface at 1.2 per cent slope.
- Area 2c — the area extending outside Areas 2a and 2b to not more than 10 km from the Area 2a boundary; obstacle surface at 1.2 per cent slope. Obstacle data for 2b, 2c, 2d is a Recommended Practice.
- Area 2d — from Areas 2a/2b/2c boundary to 45 km from the aerodrome reference point (ARP), or to the TMA boundary if closer; obstacle surface at 100 m above ground height.
Area 3 is the aerodrome movement area zone: 90 m from the runway centreline and 50 m from the edge of all other movement area surfaces. Terrain and obstacle data for Area 3 is a Recommended Practice; the obstacle collection surface is 0.5 m above the nearest movement area plane. Area 3 eTOD is required to support aerodrome mapping data consistency (A-SMGCS, runway incursion alerting).
Area 4 is the precision approach corridor for CAT II/III runways: 900 m prior to threshold and 60 m each side of the extended centreline. Where terrain beyond 900 m is mountainous, extension up to 2 000 m is a Recommended Practice. Terrain and obstacle data are a mandatory Standard for Area 4 wherever precision approach Category II or III operations exist.
Data Quality Framework
Accuracy requirements for obstacle and terrain data are based on a 90 per cent confidence level, distinguishing them from most other aeronautical data which use 95 per cent. Integrity is classified by the effect that corrupted data would have on safe flight:
- Routine — very low probability that corrupted data would severely endanger continued safe flight and landing.
- Essential — low probability of catastrophe from corrupted data.
- Critical — high probability of catastrophe from corrupted data.
Data in Area 4 and in close-in Area 2 carries the highest integrity classification because it directly underpins CAT II/III operations.
Mandatory attributes for both data set types include: area of coverage, data originator and source identifiers, acquisition method, post spacing, WGS-84 horizontal reference, horizontal and vertical accuracy, confidence levels, position, elevation reference, integrity classification, date and time stamp, and unit of measurement. Additional mandatory obstacle attributes include: obstacle identifier, horizontal extent, obstacle type, geometry type, lighting, and marking.
External Sources
- https://www.icao.int/safety/pbn/pages/electronic-terrain-and-obstacle-data.aspx - ICAO safety pages on eTOD
- https://store.icao.int/en/annex-15-aeronautical-information-services - Annex 15, Sixteenth Edition (2018) at ICAO store
- https://store.icao.int/en/procedures-for-air-navigation-services-aeronautical-information-management - Doc 10066 PANS-AIM at ICAO store
- https://www.eurocontrol.int/service/terrain-and-obstacle-data - EUROCONTROL terrain and obstacle data services and regional implementation
- https://www.aixm.aero/ - AIXM 5.2 model; eTOD obstacle and terrain exchange profiles
References
Annex 15 (Aeronautical Information Services), Sixteenth Edition (2018), Chapter 5, §5.3.3.1 — four coverage Area definitions (Areas 1, 2a/b/c/d, 3, 4) for terrain and obstacle data sets.
Annex 15, Chapter 5, §5.3.3.3 — terrain data set Standards; mandatory provision for Area 1 and Area 4; Recommended Practice for Area 2 extended and Area 3.
Annex 15, Chapter 5, §5.3.3.4 — obstacle data set Standards; mandatory for Area 1 (obstacles >=100 m), Area 2a, and Area 4 CAT II/III; Recommended Practice for Areas 2b, 2c, 2d, and 3.
Annex 15, Foreword, Amendment 33 table entry — introduction of electronic terrain and obstacle data provisions following GNSSP/4 and OCP/12-13 recommendations; applicable 25 November 2004.
Doc 10066 (PANS-AIM), First Edition (2018), Chapter 5, §5.3.3.2 — terrain and obstacle data set specifications; intended applications (TAWS, procedure design, charts, A-SMGCS).
Doc 10066, Appendix 1, Tables A1-6 and A1-8 — Aeronautical Data Catalogue numeric requirements for obstacle and terrain data by Area.
Doc 10066, Appendix 6, Tables A6-1 and A6-2 — mandatory and optional attribute lists for terrain and obstacle data sets respectively.
Doc 10066, Appendix 8, Figures A8-1 to A8-4 — graphical definitions of terrain and obstacle data collection surfaces for Areas 1, 2, 3, and 4.
Doc 10066, Chapter 4, §4.1.1 — data shall be collected and transmitted to AIS in accordance with accuracy requirements and integrity classification specified in Appendix 1.
Doc 10066, Definitions — integrity classifications (routine, essential, critical) and their risk thresholds.
Annex 6, Part I (Operation of Aircraft), Chapter 6, §6.15.1 and §6.15.2 — mandatory GPWS/TAWS requirement with forward-looking terrain avoidance; operator database management obligation.
Doc 8126 (Aeronautical Information Services Manual), Chapter 3, §3.3.3.4 — terrain and obstacle data originating from parties outside the aviation system; cost recovery and data originator arrangements.
Doc 8168 (PANS-OPS), Volume II — obstacle clearance methodology for instrument procedure design dependent on eTOD Area 2 and Area 4 data quality (authoritative source — not in local library).
Related topics
Detailed working notes on ICAO Electronic Terrain and Obstacle Data
(eTOD). This folder expands the summary in topics/etod.md into
per-aspect files so each can be read independently.
Files in this folder
overview.md— what eTOD is, where it sits in the ICAO/ATM framework, and why digital terrain data matters for modern aviation.components.md— the building blocks of eTOD: terrain dataset, obstacle dataset, coverage Areas, data quality attributes, data product specification, and metadata.blocks.md— the four coverage Areas (1, 2, 3, 4) treated as the maturity/coverage tiers of eTOD, with numeric requirements tables and a mermaid area-nesting diagram.threads.md— the six functional axes that together constitute eTOD: terrain, obstacle, data quality/integrity, collection and maintenance, exchange (AIXM), and downstream applications (PBN/TAWS/charting).modules.md— anatomy of one eTOD strand: the Area 2 obstacle data collection-to-publication chain with a worked aerodrome example.enablers.md— CNS, surveying technology, ISO standards, AIXM exchange, regulation, training, and institutional arrangements required for State eTOD compliance.performance_objectives.md— KPA-keyed performance table and KPIs for eTOD data quality and State provision.timeline.md— historical evolution: SARPS introduction, Amendment phases, PANS-AIM First Edition, and Area provision milestones.references.md— consolidated ICAO and authoritative external references for all content in this folder.
Reading order
Start with overview.md to understand what eTOD is and why it
matters, then blocks.md for the four-Area framework and numeric
requirements, then threads.md for the functional axes. components.md
provides the structural detail; modules.md gives a worked example.
enablers.md is useful for State implementation planning.
performance_objectives.md links eTOD quality to measurable outcomes.
timeline.md gives date context for amendment history.
references.md is the citation master list.
Source basis
Content is grounded in:
- ICAO Annex 15 (Aeronautical Information Services), Sixteenth Edition (2018), Chapter 5, §5.3.3 and Foreword amendment table.
- ICAO Doc 10066 (PANS-AIM), First Edition (2018), Chapter 5, §5.3.3.2 and Appendices 1, 6, and 8.
- ICAO Doc 8126 (Aeronautical Information Services Manual), Chapter 3 and Chapter 10.
- ICAO Annex 6, Part I, §6.15 (GPWS/TAWS requirements).
- ICAO Annex 14, Volume I, Chapter 4 (obstacle limitation surfaces).
- ICAO Annex 4 (Aeronautical Charts) §3.8.2.
- ICAO Doc 8168 (PANS-OPS), Volume II — obstacle clearance criteria.
What eTOD is
Electronic Terrain and Obstacle Data (eTOD) is the set of standardised digital data sets that represent, in machine-readable form, the Earth's terrain surface and the three-dimensional extent of fixed or mobile obstacles above defined data collection surfaces.
The data sets are organised into four coverage Areas (1 through 4), each calibrated to the operational application it serves. Area 1 covers an entire State territory with coarse resolution sufficient for en-route and airspace planning. Area 2 covers the vicinity of individual aerodromes with higher resolution and tighter accuracy for approach, departure, and terminal-area applications. Area 3 covers the aerodrome movement area for surface operations. Area 4 covers the precision approach corridor for CAT II/III runways with the highest accuracy requirement.
eTOD is defined as a mandatory digital data set type in Annex 15, Chapter 5. The Standards (what must be provided) and Recommended Practices (what should be provided) are stated in §5.3.3. The numerical accuracy, resolution, integrity, and post-spacing values for each Area are specified in PANS-AIM (Doc 10066), Appendices 1 and 8.
Where eTOD sits in the ICAO/ATM framework
eTOD occupies the base layer of the Digital AIM (DAIM) data product family. It is one of five digital data set types mandated by Annex 15, Chapter 5 alongside:
- AIP data set (codified aeronautical information of lasting character)
- Aerodrome mapping data set
- Instrument flight procedure data set
- (Terrain and obstacle data sets — eTOD)
Within the ASBU framework, eTOD is a foundational enabler of the DAIM thread. The DAIM-B0 module requires quality-managed digital AIS data sets to be in place, including terrain and obstacle data meeting Annex 15 standards. Higher DAIM blocks, SWIM information services, and trajectory-based PBN operations all assume that the underlying eTOD datasets are current, accurate, and distributed.
eTOD also underpins the APTA thread (approach procedure optimisation with vertical guidance), where PBN approach minima are computed using PANS-OPS obstacle clearance methodology that relies on verified Area 2 and Area 4 eTOD.
The three-layer SARPS structure
The ICAO regulatory structure for eTOD operates across three layers:
-
Annex 15 — defines the coverage Areas, the obligation to provide data, and the mandate that numerical requirements live in PANS-AIM. This provides the treaty-level obligation.
-
PANS-AIM (Doc 10066) — specifies the content, attribute lists (Appendix 6), the collection surface geometry (Appendix 8), and the numerical accuracy/integrity values (Appendix 1 Data Catalogue). This provides the operational specification.
-
Doc 8126 (AIS Manual) — provides guidance on implementation arrangements, data originator relationships, cost recovery, and cross-system consistency (e.g., keeping eTOD aligned with aerodrome mapping data for Area 3).
Why eTOD matters
The downstream effects of eTOD quality are pervasive:
Safety — TAWS/eGPWS effectiveness. Annex 6 §6.15.2 requires operators to maintain current terrain and obstacle data in their onboard terrain database. The database is built from national eTOD. If a State's Area 2 eTOD is incomplete or inaccurate, every aircraft operating in that State's terminal airspace carries a degraded TAWS terrain picture.
Safety — procedure minima. PANS-OPS (Doc 8168) obstacle clearance methodology computes procedure minima from obstacle surveys in the protected surfaces. Where eTOD Area 2 is not compliant, procedure designers must either use conservative generic assumptions or conduct proprietary surveys, raising minima.
Operational access. Conservative minima derived from poor eTOD quality directly restrict access during low-visibility operations. States with high-quality Area 2 and Area 4 eTOD can publish lower CAT II/III minima, improving operational availability.
Chart accuracy. The Aerodrome Terrain and Obstacle Chart - ICAO (Electronic) and the Precision Approach Terrain Chart - ICAO are derived from eTOD. Inaccurate eTOD produces inaccurate charts.
MSAW and A-SMGCS. Ground-based MSAW systems and A-SMGCS routing functions use eTOD as their underlying terrain reference. Gaps or errors result in false alerts or missed alerts.
Relationship to other topics in this workspace
- AIM — eTOD is one of the core Digital AIM data products; the DAIM thread depends on State provision of eTOD.
- AIXM — AIXM 5.2 includes obstacle and terrain exchange feature types; eTOD is exchanged using AIXM profiles in SWIM.
- PBN — procedure design for PBN approaches depends on Area 2 and Area 4 obstacle surveys meeting eTOD quality requirements.
- ASBU — eTOD is a DAIM-B0 foundational enabler; inadequate eTOD blocks progression to DAIM-B1 (full Digital AIM via SWIM) and APTA modules requiring improved approach procedures.
- Airspace Design — en-route airspace design and minimum altitude determination use Area 1 terrain data.
- ATFM / CDO / CCO — MSAW terrain alerting in ATM systems uses eTOD as the underlying height reference for sector minimum altitudes.
References
- Annex 15 (Aeronautical Information Services), Sixteenth Edition (2018), Chapter 5, §5.3.3 — Standards and Recommended Practices for terrain and obstacle data sets; coverage area definitions.
- Annex 15, Foreword, Amendment 33 — introduction of eTOD SARPS in 2004 following GNSSP/4 and OCP recommendations.
- Doc 10066 (PANS-AIM), First Edition (2018), Chapter 5, §5.3.3.2 — terrain and obstacle data set specifications and intended applications.
- Doc 8126 (Aeronautical Information Services Manual), Chapter 3, §3.3.3.4 — eTOD data originators outside the aviation system; arrangements for collection and cost recovery.
- Annex 6, Part I, Chapter 6, §6.15.1 and §6.15.2 — GPWS/TAWS mandate and operator terrain database maintenance obligation.
- Doc 9750 (GANP) and ASBU DAIM thread — eTOD as a DAIM-B0 foundational data product (authoritative source — not in local library; see https://ganpportal.icao.int/).
Building blocks of eTOD
eTOD comprises two distinct data set types, an organising framework of four coverage Areas, a data quality regime, a data product specification structure, and a metadata layer. Each component has a normative basis in Annex 15 and PANS-AIM.
Terrain data set
The terrain data set is a continuous grid of elevation values representing the Earth's surface. Per PANS-AIM §5.3.3.2.1:
- A terrain grid shall be angular or linear and of regular or irregular shape.
- Sets include spatial (position and elevation), thematic, and temporal aspects of the Earth's surface, covering naturally occurring features — mountains, hills, ridges, valleys, bodies of water, permanent ice and snow — and explicitly excluding obstacles.
- Depending on the acquisition method, the surface may represent the bare Earth, the top of the vegetation canopy, or something between (the "first reflective surface"). The acquisition method attribute makes this traceable.
- Only one feature type — terrain — appears in a terrain data set; obstacles must be captured in the separate obstacle data set.
Terrain attributes (all mandatory per PANS-AIM Appendix 6, Table A6-1): area of coverage, data originator identifier, data source identifier, acquisition method, post spacing, horizontal reference system, horizontal resolution, horizontal accuracy, horizontal confidence level, horizontal position, elevation, elevation reference, vertical reference system, vertical resolution, vertical accuracy, vertical confidence level, recorded surface, integrity, date and time stamp, and unit of measurement. Optional attributes: surface type, penetration level, known variations.
Obstacle data set
The obstacle data set captures the three-dimensional extent of fixed or mobile structures that penetrate defined collection surfaces. Per PANS-AIM §5.3.3.2.2:
- Obstacle elements are represented as points, lines, or polygons depending on their horizontal extent.
- All defined obstacle feature types shall be provided in a data set; each described according to mandatory attributes in Appendix 6, Table A6-2.
- Obstacles can be fixed-permanent, fixed-temporary, or mobile. Mobile and temporary types carry additional optional attributes.
- Obstacle data shall not be included in terrain data sets.
Obstacle attributes (mandatory per PANS-AIM Appendix 6, Table A6-2): area of coverage, data originator identifier, data source identifier, obstacle identifier, horizontal accuracy, horizontal confidence level, horizontal position, horizontal resolution, horizontal extent, horizontal reference system, elevation, vertical accuracy, vertical confidence level, vertical resolution, vertical reference system, obstacle type, geometry type, integrity, date and time stamp, unit of measurement, lighting, marking. Optional attributes: height, operations (for mobile types), effectivity (for temporary types).
The obstacle data product specification shall describe, for each aerodrome in the data set, the geographic coordinates and the areas covered: Areas 2a, 2b, 2c, 2d; the take-off flight path area; and the obstacle limitation surfaces.
Four coverage Areas
The four Areas are the organising framework that matches data fidelity to operational application:
Area 1: Entire State territory Terrain: mandatory Standard Obstacle: mandatory for obstacles >=100 m height above ground
Area 2: Aerodrome vicinity (subdivided 2a, 2b, 2c, 2d) Terrain 2a: mandatory Standard Obstacle 2a: mandatory Standard (surface 3 m above runway) Terrain/Obstacle 2b/2c/2d: Recommended Practice
Area 3: Aerodrome movement area zone Terrain and obstacle: Recommended Practice (required to support aerodrome mapping data consistency)
Area 4: CAT II/III precision approach corridor Terrain and obstacle: mandatory Standard
Data quality attributes
PANS-AIM §5.3.3.2 and Appendix 1 establish the quality framework for eTOD data elements. The key dimensions are:
Accuracy — for terrain and obstacle data, accuracy requirements are based on a 90 per cent confidence level, distinguishing them from most aeronautical data (95 per cent). Post spacing (grid density) and horizontal/vertical accuracy vary by Area, with Area 4 having the tightest requirements.
Resolution — the minimum difference between values that can be distinguished; applies independently to horizontal and vertical dimensions. Resolution requirements are captured in the Aeronautical Data Catalogue (Appendix 1).
Integrity — the degree of assurance that data has not been lost or altered since origination or authorised amendment. Three classes:
- Routine: 1 x 10^-3 probability of undetected error per flight hour.
- Essential: 1 x 10^-5 probability.
- Critical: 1 x 10^-8 probability. Area 4 data and close-in Area 2 obstacle data carry Critical integrity because corrupted data has a high probability of endangering safe flight during a CAT II/III approach.
Traceability — the chain from field survey through processing to distribution; captured via originator and source identifiers, date and time stamps, and acquisition method attributes.
Timeliness — data must be current; operators and AIS providers must maintain update schedules aligned with survey programmes and aerodrome infrastructure changes.
Data product specification
Per ISO 19100 series geographic information standards, each eTOD data set is described by a data product specification that defines: the scope (Area, aerodrome, State); the spatial reference system; the data content model; the data quality requirements; the acquisition method; the update policy; and the data distribution format. PANS-AIM Appendix 6 Table A6-1/A6-2 provide the ICAO-specific attribute requirements that populate each specification.
The terrain data product specification for Area 1 is typically a State-wide digital elevation model (DEM). The obstacle data product specifications are aerodrome-specific, covering the defined Areas 2 and 4 for each aerodrome in the data set.
Metadata
Each data set shall be provided to the next intended user together with at least the minimum set of metadata that ensures traceability (Annex 15 §5.3.1.2). For data sets with geographic information — terrain, obstacle, and aerodrome mapping — metadata may be structured according to ISO Standard 19115: Geographic information — Metadata (Doc 8126 §2.3.3.3). This enables interoperability with geographic information systems (GIS) and AIXM-based exchange services.
Hierarchy of eTOD components
- eTOD
- Terrain data set
- Grid (Area 1: State-wide DEM)
- Grid (Area 2: aerodrome vicinity DEM, within 10 km of ARP)
- Grid (Area 3: movement area surface)
- Grid (Area 4: CAT II/III corridor)
- Obstacle data set
- Obstacle records (Area 1: >=100 m obstacles, State-wide)
- Obstacle records (Area 2a/2b/2c/2d: aerodrome obstacles)
- Obstacle records (Area 3: movement area penetrations)
- Obstacle records (Area 4: CAT II/III corridor penetrations)
- Data quality attributes
- Accuracy (horizontal and vertical, 90% confidence)
- Resolution (post spacing, vertical resolution)
- Integrity (routine / essential / critical)
- Traceability (originator, source, acquisition method, timestamp)
- Data product specification (per ISO 19100 series)
- Metadata (per ISO 19115)
- Terrain data set
References
- Annex 15, Chapter 5, §5.3.3 — Standards and Recommended Practices for terrain and obstacle data sets; coverage Area definitions; mandatory and Recommended Practice obligations per Area.
- Doc 10066 (PANS-AIM), Chapter 5, §5.3.3.2.1 — terrain data set specifications; feature type, spatial content, acquisition method recording.
- Doc 10066, Chapter 5, §5.3.3.2.2 — obstacle data set specifications; point/line/polygon representation; product specification area coverage.
- Doc 10066, Appendix 6, Table A6-1 — mandatory and optional terrain attributes.
- Doc 10066, Appendix 6, Table A6-2 — mandatory and optional obstacle attributes.
- Doc 10066, Appendix 1 — Aeronautical Data Catalogue; Tables A1-6 (obstacle) and A1-8 (terrain); numeric accuracy, resolution, and integrity requirements by Area.
- Doc 10066, Definitions — integrity classifications (routine, essential, critical) and their probability thresholds.
- Doc 10066, Chapter 4, §4.1.1 — collection and transmission requirements conforming to accuracy and integrity in Appendix 1.
- Doc 8126 (AIS Manual), Chapter 2, §2.3.3.3 — metadata per ISO 19115 for geographic data sets including terrain and obstacle.
The four Areas as coverage tiers
For eTOD, the analogue of ASBU Blocks is the four coverage Areas defined in Annex 15 §5.3.3.1. Each Area is a progressive tier of spatial coverage and data fidelity, building from State-level terrain (Area 1) through aerodrome vicinity (Area 2), movement area surface (Area 3), to precision approach corridor (Area 4).
Each Area has a defined:
- Spatial extent — what geography it covers.
- Collection surface — the surface above which obstacles must be captured and below which terrain is gridded.
- Obligation level — Standard (shall) or Recommended Practice (should) from Annex 15.
- Intended applications — the safety systems and procedures that depend on that Area's data.
Area nesting diagram
Area 1 — State territory
Spatial extent. The entire territory of a State.
Terrain obligation. Mandatory Standard. Terrain data shall be provided for Area 1 (Annex 15 §5.3.3.3.2). No terrain type is excluded from the obligation; the grid covers the full State boundary.
Obstacle obligation. Mandatory Standard for obstacles whose height above ground is 100 m or higher (Annex 15 §5.3.3.4.3). This threshold captures the principal enroute hazards — tall towers, wind turbine farms, large industrial structures — while excluding the vast majority of low-height features that are managed at the aerodrome level.
Intended applications. En-route MSAW terrain reference; airspace design minimum altitude determination; flight simulator databases; State-level terrain awareness for operators flying in the State.
Typical data source. National mapping agencies, satellite-derived digital elevation models (DEMs), SRTM or ASTER-type sources processed to meet Annex 15 accuracy, reprocessed through an ISO 19115 compliant metadata record citing the acquisition method and date.
Area 2 — Aerodrome vicinity
Area 2 is the most operationally complex of the four Areas because it is sub-divided and because the required accuracy is substantially higher than Area 1 to support instrument procedure design.
Area 2 as a whole. Covers the vicinity of an aerodrome regularly used by international civil aviation, extending up to 45 km from the aerodrome reference point (ARP), or to the TMA boundary if nearer.
Area 2a
Spatial extent. The runway strip (as defined in Annex 14 Vol I Chapter 3) plus any clearway that exists.
Terrain obligation. Mandatory Standard. Terrain data shall be provided for Area 2a (Annex 15 §5.3.3.3.3(a)).
Obstacle obligation. Mandatory Standard. Obstacles that penetrate a collection surface 3 m above the nearest runway elevation measured along the runway centreline, and for clearway portions at the nearest runway end elevation (Annex 15 §5.3.3.4.5(a)).
Also mandatory: objects in the take-off flight path area projecting above a 1.2 per cent slope surface (Annex 15 §5.3.3.4.5(b)); penetrations of aerodrome obstacle limitation surfaces (§5.3.3.4.5(c)).
Why it matters. Area 2a data is the direct input to the Obstacle Departure Procedure (ODP) design and determines whether a standard SID can be published or a specific ODP is needed. Errors in Area 2a obstacle data can invalidate existing procedures.
Area 2b
Spatial extent. Departure corridor extending from the ends of Area 2a, 10 km in length, with a 15 per cent splay to each side.
Obstacle collection surface. 1.2 per cent slope upward from the ends of Area 2a at the elevation of the runway end.
Obligation. Recommended Practice (Annex 15 §5.3.3.4.6). Minimum height threshold: 3 m above ground in Area 2b.
Area 2c
Spatial extent. Area extending outside Areas 2a and 2b, to not more than 10 km from the boundary of Area 2a.
Obstacle collection surface. 1.2 per cent slope; initial elevation is the elevation of the point of Area 2a at which it commences.
Obligation. Recommended Practice. Minimum height threshold: 15 m above ground in Area 2c.
Area 2d
Spatial extent. From the boundaries of Areas 2a/2b/2c out to 45 km from the ARP, or to an existing TMA boundary, whichever is nearest.
Obstacle collection surface. Obstacles 100 m above ground height.
Obligation. Recommended Practice. Captures tall structures that penetrate the terminal airspace but lie beyond the closer coverage areas.
Practical note. Area 2b, 2c, 2d data, while Recommended Practice, are required by many PANS-OPS-compliant procedure designs to confirm that no tall structures invalidate the protected surfaces. States that omit them often find that procedure designers must conduct proprietary surveys before publishing instrument approaches.
Area 3 — Aerodrome movement area
Spatial extent. The area bordering the aerodrome movement area: 90 m horizontally from the runway centreline and 50 m from the edge of all other parts of the movement area.
Collection surface. 0.5 m above the horizontal plane passing through the nearest point on the aerodrome movement area.
Obligation. Recommended Practice for both terrain and obstacle data (Annex 15 §5.3.3.3.7 and §5.3.3.4.9).
Operational rationale. Area 3 eTOD is the foundation for:
- A-SMGCS routing and ground incursion alerting.
- Aerodrome mapping data consistency: PANS-AIM §5.3.3.3.1 states that aerodrome mapping data should be supported by Area 3 eTOD to ensure consistency of all geographical data related to the aerodrome.
- Moving-map displays for surface operations.
Area 3 eTOD and aerodrome mapping data can be originated using common acquisition techniques and managed within a single GIS.
Area 4 — CAT II/III precision approach corridor
Spatial extent. 900 m prior to the runway threshold and 60 m each side of the extended runway centreline, in the direction of approach, for precision approach runways CAT II or III. Where terrain beyond 900 m is mountainous or otherwise significant, extension up to 2 000 m from threshold is a Recommended Practice.
Obligation. Mandatory Standard for terrain and obstacle data for all CAT II/III runways (Annex 15 §5.3.3.3.8 and §5.3.3.4.10).
Operational rationale. The Precision Approach Terrain Chart - ICAO is derived primarily from Area 4 terrain data and Area 2 obstacle data. Operators use Area 4 data to assess the effect of terrain on decision height determination by use of radio altimeters. Accurate Area 4 data can allow lower published decision heights on CAT III runways.
Numeric requirements summary
| Area | Terrain obligation | Obstacle obligation | Key accuracy driver |
|---|---|---|---|
| Area 1 | Mandatory — entire State | Mandatory — obstacles >=100 m AGL | En-route MSAW, airspace design |
| Area 2a | Mandatory | Mandatory — 3 m surface, OLS, take-off path | ODP/SID design, PANS-OPS minima |
| Area 2b | Recommended Practice | Recommended — 1.2% slope, 3 m min | Departure procedures |
| Area 2c | Recommended Practice | Recommended — 1.2% slope, 15 m min | Terminal area procedures |
| Area 2d | Recommended Practice | Recommended — 100 m AGL | Terminal area tall structures |
| Area 3 | Recommended Practice | Recommended — 0.5 m surface | A-SMGCS, aerodrome mapping |
| Area 4 | Mandatory — CAT II/III runways | Mandatory — CAT II/III runways | Precision approach, decision height |
Numerical post-spacing, horizontal accuracy, vertical accuracy, and integrity classification values for each Area are specified in the PANS-AIM Appendix 1 Aeronautical Data Catalogue (Tables A1-6 and A1-8). The tightest requirements apply to Area 4 and Area 2a (critical integrity classification); Area 1 carries routine integrity for terrain but essential integrity for tall obstacles.
Area implementation sequencing
A practical State eTOD implementation sequence follows this order:
- Area 1 terrain — covers the whole State for en-route safety. Achievable with national DEM or processed satellite data.
- Area 1 obstacles — systematic survey of all structures
=100 m AGL; often the hardest collection task at State level.
- Area 2a/4 terrain and obstacles at each international aerodrome — highest priority because CAT II/III approvals, procedure design, and TAWS databases all depend on these.
- Area 2b/2c/2d — extend progressively outward; driven by procedure design demand and height of surrounding terrain.
- Area 3 — movement area surface data; typically coordinated with aerodrome mapping data programmes.
References
- Annex 15, Chapter 5, §5.3.3.1 — four Area definitions with spatial extent boundaries.
- Annex 15, Chapter 5, §5.3.3.3.2, §5.3.3.3.3, §5.3.3.3.8 — terrain Standards and Recommended Practices by Area.
- Annex 15, Chapter 5, §5.3.3.4.3 to §5.3.3.4.11 — obstacle Standards and Recommended Practices by Area including height thresholds.
- Annex 15, Chapter 5, §5.3.3.2 — Recommended Practice on Area 4 length extension to 2 000 m for mountainous terrain.
- Doc 10066 (PANS-AIM), Appendix 8, Figures A8-1 to A8-4 — graphical terrain and obstacle collection surface definitions for each Area.
- Doc 10066, Appendix 1, Tables A1-6 and A1-8 — numeric accuracy, resolution, and integrity requirements by Area.
- Doc 10066, Chapter 5, §5.3.3.3.1 — aerodrome mapping data to be supported by Area 3 eTOD for consistency.