GACA Obstruction Lighting: What a Tall Building Needs

Obstruction lighting tends to come up late in a project — usually when a height consultant or the civil defense review flags it, by which point the façade design and electrical risers are already fixed. It is worth understanding early instead, because the specification is not a design choice. It comes from a published international standard that Saudi Arabia enforces directly, and it determines fixture type, placement and monitoring, not just whether a red light goes on the roof.

Where the Requirement Comes From

Obstruction lighting in Saudi Arabia is governed by GACAR Part 139, the General Authority of Civil Aviation's regulation for the certification, authorization and operation of aerodromes. Part 139 is aligned with ICAO Annex 14 Volumes I and II, and its Subpart I — Visual Aids for Denoting Obstacles, specifically sections 139.601 and 139.603 — sets out when an object has to be marked and lit, and to what specification.

In practice this means a structure is not assessed in isolation. Whether a building needs obstruction lighting, and at what intensity, depends on its height, its position relative to any nearby aerodrome's approach and take-off surfaces, and whether an aeronautical study has flagged it as significant. A 40-metre building a long way from any flight path may need nothing. A shorter building sitting inside an approach surface near an airport can need lighting a much taller building elsewhere would not.

The Three Intensity Classes

ICAO Annex 14 Table 6-1 defines obstacle lights across three intensity bands, and the general guidance in the standard links them to height: low-intensity lighting for objects under roughly 45 metres above ground level, medium-intensity between about 45 and 150 metres, and high-intensity above 150 metres — though the exact requirement for a given structure is set by the aeronautical study for its location, not by height alone.

Low-intensity Type A is a fixed red light rated at 10 candela; Type B is a fixed red light at 32 candela. Both are steady-burning, not flashing, and are the most common choice for a standalone structure below the height threshold.

Medium-intensity comes in three types: Type A is a flashing white light at 20,000 candela by day and twilight, dropping to 2,000 candela at night; Type B is a flashing red light at 2,000 candela, for night use; Type C is a fixed red light, also 2,000 candela, for night use. A building using Type A by day still needs a night-time pairing, since Type A's daytime intensity would be far too bright after dark — the standard sets separate day, twilight and night output for exactly this reason.

High-intensity lighting is for the tallest structures: Type A reaches 200,000 candela by day, dropping to 20,000 at twilight and 2,000 at night; Type B peaks lower, at 100,000 candela by day. Both flash. At this intensity the light is genuinely bright enough to be a dazzle risk to pilots operating near it, which is why the standard also allows a dual system — switching to a lower-intensity red light at night within about 10 kilometres of an aerodrome, where a flashing white strobe after dark would do more harm than good.

Placement Isn't Just 'One Light on Top'

For a structure over 45 metres, a single light at the apex does not satisfy the standard. ICAO Annex 14 requires intermediate levels of lighting spaced down the structure — no more than 105 metres apart for medium-intensity Type A or high-intensity Type A, and no more than 52 metres apart where Type B or Type C is used — so the outline of the building is marked at multiple heights, not just at the top.

The lights also have to be arranged so the object is visible from every direction in azimuth. If part of the structure's own geometry shields a light from one approach angle, an additional fixture has to go on the part doing the shielding, not just at the original planned position. This is where a lighting layout drawn from floor plans alone tends to miss something — the obstruction lighting design has to account for the building's actual silhouette from the air, which is a different exercise from architectural lighting.

Why Monitoring Matters More Than the Light Itself

A failed obstruction light is not a cosmetic problem. It is the one thing the system exists to prevent — the structure going unmarked at night without anyone on the ground knowing. A lamp that silently fails and stays dark until the next scheduled inspection has effectively taken the building out of compliance for however long that gap is, and nobody involved in operating the building would know until an inspector asks, or worse.

That is why a properly specified obstruction lighting installation includes a monitored control panel that raises an alarm on fixture failure, rather than relying on periodic visual checks from the ground. It is also why circuits feeding obstruction lighting are normally backed so that a loss of the building's normal supply does not take the warning lights out along with it — the risk the lighting exists to manage does not go away just because the building lost power.

What This Means at the Design Stage

The costly version of this is finding out after the structure is built that it needs obstruction lighting, or that what was installed does not meet the applicable intensity class. Getting an aeronautical assessment early — ideally during design, not after the façade is finished — determines the intensity class, the number of levels required, and whether a dual day/night system applies, while there is still room to route the supporting electrical circuits sensibly.

For a helipad on the same structure, the lighting requirement is separate again — perimeter lighting, touchdown and lift-off area marking, and an illuminated windsock, following the approved helipad geometry rather than the obstruction marking rules above. A high-rise with a rooftop helipad typically needs both systems specified together, on a shared monitored panel, so a facilities team is managing one alarm source instead of two.