AIM ¶ 2-2-3 — Obstruction Lights
AIM 2-2-3 explains obstruction lighting types: red beacons, white flashing lights, dual systems, and catenary markers for towers and powerlines.
In Plain English
AIM 2-2-3 describes how obstructions like towers, chimneys, and powerlines are marked and lit so pilots can see them day and night. Knowing the lighting scheme helps you identify hazards during low-altitude flight, night operations, and VFR navigation.
The main systems are:
- Aviation Red Obstruction Lights: Flashing red beacons (20–40 flashes/min) and steady red lights at night, paired with aviation orange and white paint for daytime.
- Medium Intensity Flashing White: Used day and twilight, dimmed at night. On structures 500 ft AGL or less, paint and other lighting can be omitted. Not normally used below 200 ft AGL.
- High Intensity White: Flashing white day, reduced at night/twilight. Replaces red lights and paint.
- Dual Lighting: Red lights at night + high intensity white during the day; paint may be omitted.
- Catenary Lighting: Marks high-voltage (69KV+) powerlines crossing rivers, gorges, etc. Flashes in a middle-top-lower sequence (~60 flashes/min) to outline the wire span.
Tall chimneys and towers may have 360° high intensity white lights at 40 flashes/min, with multiple vertical levels flashing simultaneously. This is informational guidance — useful for hazard awareness during preflight planning and low-level flight.
AIM Source Text
FAA AIM ¶ 2-2-32-2-3. 2-2-3. Obstruction Lights
Obstructions are marked/lighted to warn airmen of their presence during daytime and nighttime conditions. They may be marked/lighted in any of the following combinations: Aviation Red Obstruction Lights. Flashing aviation red beacons (20 to 40 flashes per minute) and steady burning aviation red lights during nighttime operation. Aviation orange and white paint is used for daytime marking. Medium Intensity Flashing White Obstruction Lights. Medium intensity flashing white obstruction lights may be used during daytime and twilight with automatically selected reduced intensity for nighttime operation. When this system is used on structures 500 feet (153m) AGL or less in height, other methods of marking and lighting the structure may be omitted. Aviation orange and white paint is always required for daytime marking on structures exceeding 500 feet (153m) AGL. This system is not normally installed on structures less than 200 feet (61m) AGL. High Intensity White Obstruction Lights. Flashing high intensity white lights during daytime with reduced intensity for twilight and nighttime operation. When this type system is used, the marking of structures with red obstruction lights and aviation orange and white paint may be omitted. Dual Lighting. A combination of flashing aviation red beacons and steady burning aviation red lights for nighttime operation and flashing high intensity white lights for daytime operation. Aviation orange and white paint may be omitted. Catenary Lighting. Lighted markers are available for increased night conspicuity of high-voltage (69KV or higher) transmission line catenary wires. Lighted markers provide conspicuity both day and night. Medium intensity omnidirectional flashing white lighting system provides conspicuity both day and night on catenary support structures. The unique sequential/simultaneous flashing light system alerts pilots of the associated catenary wires. High intensity flashing white lights are being used to identify some supporting structures of overhead transmission lines located across rivers, chasms, gorges, etc. These lights flash in a middle, top, lower light sequence at approximately 60 flashes per minute. The top light is normally installed near the top of the supporting structure, while the lower light indicates the approximate lower portion of the wire span. The lights are beamed towards the companion structure and identify the area of the wire span. High intensity flashing white lights are also employed to identify tall structures, such as chimneys and towers, as obstructions to air navigation. The lights provide a 360 degree coverage about the structure at 40 flashes per minute and consist of from one to seven levels of lights depending upon the height of the structure. Where more than one level is used the vertical banks flash simultaneously.
Oral Exam Questions a DPE Might Ask
Q1What are the different types of obstruction lighting systems described in the AIM?
Per AIM 2-2-3, obstruction lighting includes Aviation Red Obstruction Lights (flashing red beacons and steady red), Medium Intensity Flashing White, High Intensity White, Dual Lighting (red at night plus high intensity white by day), and Catenary Lighting for high-voltage transmission wires.
Q2When can aviation orange and white paint be omitted on an obstruction?
Per AIM 2-2-3, paint may be omitted when High Intensity White Obstruction Lights or Dual Lighting are used, or when Medium Intensity Flashing White lights are used on structures 500 ft AGL or less. Paint is always required on structures over 500 ft AGL using medium intensity systems.
Q3How are high-voltage transmission line catenary wires marked, and why is this important?
Per AIM 2-2-3, catenary wires on lines of 69KV or higher crossing rivers, chasms, or gorges may use high intensity flashing white lights on supporting structures, flashing in a middle-top-lower sequence at about 60 flashes per minute to identify the wire span area — critical for pilots flying low-level over such terrain.
Related Paragraphs in AIM Chapter 2