Definition
Steady-burning or flashing red lights mounted on tall structures such as towers, antennas, buildings, and cranes to make them visible to pilots at night. They mark obstructions that could pose a hazard to aircraft and are typically used either alone or in combination with other red lights at the top and intermediate levels of the structure.
Plain English
Red lights placed on tall objects so pilots can see them and avoid hitting them, especially at night.
Context Anchor
Seen on or near airports and along flight routes, especially on tall structures or obstacles that may be hard to see at night.
Derivation
“Obstruction” comes from older words meaning to block or build against something. In aviation, an obstruction is something that may block or interfere with the safe path of an aircraft, so the light marks that object clearly.
Why Pilots Care
They provide the primary visual cue for avoiding fixed obstructions at night or in low visibility, directly reducing mid-air collision risk with towers and antennas.
Intuition Check
Do not think of these as traffic lights or runway lights. Red obstruction lights do not give instructions; they simply mark a hazard so you can avoid it.
Example Sentence 1
On the night cross-country, the pilot picked up the red obstruction lights on the broadcast tower well before reaching the ridge.
Example Sentence 2
While reviewing the sectional for the night flight, the pilot noted the red obstruction lights marking a 1,200-foot antenna east of the airport.