What is Electronic Terrain and Obstacle Data (eTOD)?
Definition
An eTOD data set is a digital record of terrain heights and obstacles in one of four defined areas, with set accuracy and integrity.
The data feeds air navigation. It is not a drawing. A State or an aerodrome operator supplies it to the aeronautical information services, and users take it from there. The European ATM Master Plan says that States provide terrain and obstacle data for their own territory.
Three nearby pages cover different things. The aerodrome obstacle chart page covers the ICAO charts. The obstacle limitation surface page covers the airspace that must stay free. This page covers the data sets and their numerical requirements.
The four areas
The EASA guidance (GM4 ADR.OPS.A.005(a)) splits the coverage into four areas.
| Area | Extent |
|---|---|
| Area 1 | The entire territory of the State |
| Area 2 | The aerodrome surroundings, split into 2a to 2d |
| Area 3 | The strip that borders the aerodrome movement area |
| Area 4 | The area before the threshold of a Category II or III precision approach runway |
Area 2 has four parts.
- Area 2a is a rectangle around a runway. It holds the runway strip and any clearway.
- Area 2b starts at the ends of Area 2a and runs in the direction of departure. It is 10 km long and splays 15 percent to each side.
- Area 2c lies outside Areas 2a and 2b, at most 10 km from the boundary of Area 2a.
- Area 2d lies outside Areas 2a, 2b and 2c. It reaches 45 km from the aerodrome reference point, or to the terminal control area boundary, whichever is nearer.
Area 3 reaches 90 m from the runway centre line along a runway. It reaches 50 m from the edge of all other parts of the movement area.
Area 4 starts 900 m before the threshold. It is 60 m wide on each side of the extended runway centre line. Where the terrain beyond 900 m is mountainous or otherwise significant, the length of Area 4 should grow to at most 2,000 m.
Accuracy tables
The EASA guidance gives two numerical tables. They are guidance material, so the verb is “should”. The tables below repeat them.
| Area 1 | Area 2 | Area 3 | Area 4 | |
|---|---|---|---|---|
| Post spacing | 3 arc seconds (about 90 m) | 1 arc second (about 30 m) | 0.6 arc seconds (about 20 m) | 0.3 arc seconds (about 9 m) |
| Vertical accuracy | 30 m | 3 m | 0.5 m | 1 m |
| Vertical resolution | 1 m | 0.1 m | 0.01 m | 0.1 m |
| Horizontal accuracy | 50 m | 5 m | 0.5 m | 2.5 m |
| Confidence level | 90 % | 90 % | 90 % | 90 % |
| Data classification | Routine | Essential | Essential | Essential |
Obstacle data
| Area 1 | Area 2 | Area 3 | Area 4 | |
|---|---|---|---|---|
| Vertical accuracy | 30 m | 3 m | 0.5 m | 1 m |
| Vertical resolution | 1 m | 0.1 m | 0.01 m | 0.1 m |
| Horizontal accuracy | 50 m | 5 m | 0.5 m | 2.5 m |
| Confidence level | 90 % | 90 % | 90 % | 90 % |
| Data classification | Routine | Essential | Essential | Essential |
The maintenance period is “as required” in every area. The obstacle table has no post spacing, because an obstacle is a feature and not a grid of points.
ICAO states that the accuracy and integrity classes for aerodrome data are in PANS-AIM (Doc 10066), Appendix 1 (Annex 14, 2.1.1, Note). This page did not open PANS-AIM. It gives the EASA values only.
Which terrain and obstacles enter the data set
Each area has a collection surface. An object enters the data set when it rises above that surface (GM4 ADR.OPS.A.005(a)).
| Area | Obstacle collection surface |
|---|---|
| Area 1 | Every obstacle 100 m or higher above ground |
| Area 2a | 3 m above the nearest runway elevation along the centre line. For a clearway, the elevation of the nearest runway end |
| Area 2b | A 1.2 % slope from the ends of Area 2a, at the elevation of the runway end |
| Area 2c | A 1.2 % slope that starts at the elevation of the point of Area 2a where it starts |
| Area 2d | 100 m above ground |
| Area 3 | 0.5 m above the horizontal plane through the nearest point of the movement area |
Terrain has its own rules in Area 2. Within 10 km of the aerodrome reference point, terrain data meets the Area 2 values. Between 10 km and the terminal control area boundary or a 45 km radius, whichever is smaller, the test is a plane. Terrain above a plane 120 m over the lowest runway elevation meets the Area 2 values. Terrain below it meets the Area 1 values.
Who provides the data
Two layers share the duty.
The State. The European ATM Master Plan names three texts. They are Regulation (EU) 2017/373, ICAO Annex 15 and PANS-AIM. They require States to provide terrain and obstacle data for their own territory. ICAO Annex 14 says that the extent of the obstacle limitation surfaces is used in defining the collection requirement. It says that Annex 15, Chapter 5 holds the provisions on the data sets. That Annex 14 text applies from 21 November 2030 (Chapter 4, Note 2).
The aerodrome operator. Regulation (EU) No 139/2014, ADR.OPS.A.005, makes the operator determine, document and maintain the data about the aerodrome. The operator provides it to users and to the air traffic services and aeronautical information services providers. The acceptable means of compliance (AMC1 ADR.OPS.A.005) say the following.
- The operator should measure and report obstacles and terrain in Area 3 and in the part of Area 2 inside the aerodrome boundary. The unit is degrees, minutes, seconds and tenths of seconds.
- It should also report the top elevation, type, marking and lighting, if any, of each obstacle.
- It should provide electronic obstacle data for all obstacles in Area 2 inside the boundary that it assesses as a hazard to air navigation.
- It should provide electronic terrain and obstacle data for three sets of penetrations. They are the penetrations of the Area 2a collection surface, of the take-off flight path area obstacle identification surfaces and of the obstacle limitation surfaces.
- It should provide electronic terrain and obstacle data for Area 4 on runways with Category II or III precision approach operations. This applies where operators need detailed terrain data for radio altimeter decision heights.
- For data outside the boundary, it should make arrangements with the air traffic services providers and the competent authority.
ICAO Annex 14, 2.5.5, writes the first two points as a Standard. It uses “shall” for the coordinates of obstacles in Area 2 inside the boundary and in Area 3. It also uses “shall” for the top elevation, type, marking and lighting.
Data quality in the EU
ADR.OPS.A.010 is a rule, not guidance. It comes from Delegated Regulation (EU) 2020/2148. The aerodrome operator shall have formal arrangements with the organisations with which it exchanges aeronautical data. It shall ensure these properties of the data:
- the required quality at origination, kept through transmission
- the accuracy that the aeronautical data catalogue sets
- integrity from origination to transmission, by class
- resolution that suits the real accuracy
- traceability
- timeliness
- completeness
- a delivery format that meets the specification
For essential data, corruption must not occur at any stage of the process (ADR.OPS.A.010(c)(2)). Area 2, 3 and 4 data fall in that class in the EASA tables.
The AMC lists the parties that the arrangements should cover. They include the providers of survey data, procedure design, electronic terrain data and electronic obstacle data (AMC2 ADR.OPS.A.010). The minimum content has several items. They include the data to provide, the quality requirements and the proof of conformity. They also include the action on a data error, the criteria for notifying a change and the metadata.
What it means on an airfield
An obstacle record in an eTOD data set carries a position, a top elevation, a type, a marking and a lighting attribute. The marking and the lighting on the ground must match the record. An obstacle light that fails or changes makes the record wrong. The operator reports the change to the aeronautical information services through the formal arrangements.
The values are tight in Area 3. It needs 0.5 m horizontal and 0.5 m vertical accuracy at a 90 % confidence level. A survey must show that it reaches those values. Area 2 needs 5 m and 3 m.
EASA also names the electronic chart in its low-visibility rules. For a Category I or II special authorisation operation, the pre-threshold terrain must be surveyed. A precision approach terrain chart or the electronic chart must hold the data (AMC1 ADR.OPS.B.045(a)(2)).
What TarmacView does and does not do
TarmacView keeps an obstacle register with the polygon, type and height above ground, mean sea level and ellipsoid of each obstacle. It exports the register on the airport data sheet. The register is not an eTOD data set. TarmacView has no eTOD, AIXM or chart output. The State is responsible for the obstacle register. The obstacle limitation surface survey is in development and is not offered yet.
Frequently Asked Questions
- What is electronic terrain and obstacle data (eTOD)?
- An eTOD data set is a digital record of terrain heights and obstacles in one of four defined areas, with set accuracy and integrity. EASA guidance names four areas. Area 1 is the whole State. Area 2 is the aerodrome surroundings. Area 3 is the movement area. Area 4 is the area before a Category II or III runway.
- What accuracy does eTOD require for obstacle data?
- The EASA guidance sets it per area, at a 90 % confidence level. Horizontal accuracy is 50 m in Area 1, 5 m in Area 2, 0.5 m in Area 3 and 2.5 m in Area 4. Vertical accuracy is 30 m, 3 m, 0.5 m and 1 m. Areas 2 to 4 are essential data. Area 1 is routine data.
- What are Area 2, Area 3 and Area 4 in eTOD?
- Area 2 is the aerodrome surroundings, split into Areas 2a to 2d. It reaches 45 km from the aerodrome reference point or to the terminal control area boundary. Area 3 borders the movement area. Area 4 is the 900 m before the threshold of a Category II or III precision approach runway. It is 60 m wide on each side of the centre line.
- How accurate must eTOD terrain data be?
- The EASA guidance gives a post spacing and a vertical accuracy per area. Area 1 has 3 arc seconds (about 90 m) and 30 m. Area 2 has 1 arc second (about 30 m) and 3 m. Area 3 has 0.6 arc seconds (about 20 m) and 0.5 m. Area 4 has 0.3 arc seconds (about 9 m) and 1 m.
- Who must provide eTOD?
- The State provides it for its own territory, under ICAO Annex 15 and PANS-AIM. EASA guidance says that the aerodrome operator should report obstacle and terrain data in Area 3. It also reports them in the part of Area 2 inside the boundary. For data outside the boundary, it should make arrangements with the air traffic services provider and the competent authority.
- Which obstacles go into an eTOD data set?
- Those that penetrate the collection surface of the area. In Area 2a the surface is 3 m above the nearest runway elevation. In Area 2d it is 100 m above ground. In Area 3 it is 0.5 m above the plane through the nearest point of the movement area. In Area 1, every obstacle of 100 m or more above ground goes in.
- What is the difference between eTOD and an aerodrome obstacle chart?
- The eTOD is the data. The aerodrome terrain and obstacle chart - ICAO (Electronic) is a chart that Annex 4 describes. The EASA rules name the electronic chart as one way to hold surveyed pre-threshold terrain. The other way is a precision approach terrain chart.
- Does TarmacView produce eTOD?
- No. TarmacView keeps an obstacle register with the polygon, type and height of each obstacle. The register is not an eTOD data set. TarmacView has no AIXM or eTOD export. The obstacle limitation surface survey is in development.
References
- easa-ear-aerodromes
- Easy Access Rules for Aerodromes (Regulation (EU) No 139/2014), including CS-ADR-DSN Issue 7 EASA
- icao-annex-14-vol1
- Annex 14 to the Convention on International Civil Aviation, Aerodromes, Volume I, Aerodrome Design and Operations, Ninth Edition (July 2022, consolidated with later amendments) ICAO
- atm-master-plan-inf07
- INF07 - Electronic Terrain and Obstacle Data (eTOD) European ATM Master Plan
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
