I was thinking that red lights on the antennas on buildings help aircraft to see if there are tall objects in the ground. Is this right? normal hazard light


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    $\begingroup$ Try this. Synchronize your eyes to the blinking of the lights such that you never see them on. While maintaining your blink speed and duration, spin around in a circle (slower makes it easier for you). When you get back around, find the tower. At night, this is really, really, really hard. Imagine doing that in an airplane... $\endgroup$
    – corsiKa
    Commented Feb 25, 2016 at 20:39
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    $\begingroup$ @corsika I don't understand the point of the blinking and spinning exercise. $\endgroup$
    – J W
    Commented Feb 25, 2016 at 21:55
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    $\begingroup$ No, the red lights are for the pilots to see. Very few aircraft (maybe some drones?) are capable of seeing things. $\endgroup$
    – jamesqf
    Commented Feb 25, 2016 at 22:17
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    $\begingroup$ @JonathanWalters You're trying to see what the towers look like without the lights on. It's a lot easier (and fun!) to just synchronize your eyes to their blink such that you never see the lights on than it is to actually turn the lights off. Also safer. You spin around so it's harder to cheat from when you saw the lights on. Bonus: once you play around with it, you can play games with the lights and have them shoot other lights!! Takes a while to learn how but once you do it's super fun. $\endgroup$
    – corsiKa
    Commented Feb 26, 2016 at 0:27
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    $\begingroup$ @corsika OK, in other words, an unlighted building or tower is hard to see... $\endgroup$
    – J W
    Commented Feb 26, 2016 at 2:59

4 Answers 4


Those lights are used to show obstacles that may interfere with the aircraft's course, such as antennas, buildings, wind turbines, and they are mandatory. The name of those lights is Aircraft Warning Lights, and here is an article from Wikipedia about them.

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    $\begingroup$ I was in a city-wide power blackout once (rain flooding the electrical substations), and it was notable that (apart from a hospital and car headlights) the only signs of electricity were those aircraft warning lights on (all) the tall buildings ... i.e. fwiw they're important enough to have backup (battery or generator) power. $\endgroup$
    – ChrisW
    Commented Feb 25, 2016 at 18:22
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    $\begingroup$ @ChrisW: In a lot of countries they are so important that they are run by dual backup batteries, sometimes plus generator and every light you visually see is run by at least two bulbs. $\endgroup$
    – PlasmaHH
    Commented Feb 25, 2016 at 20:32
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    $\begingroup$ I've seen the control panel for one of these "lights" in a water tower, and it's amazing how complex it is for a simple light. Multiple redundancies and backup power sources. $\endgroup$
    – JPhi1618
    Commented Feb 25, 2016 at 21:41
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    $\begingroup$ @JPhi1618 it makes sense, since their failure leads to very, very big problems. $\endgroup$
    – Nelson
    Commented Feb 26, 2016 at 6:25
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    $\begingroup$ Lights are increasingly useful for situational awareness when visibility worsens for any reason (night, fog, rain...) $\endgroup$
    – mins
    Commented Feb 26, 2016 at 16:49

Yes, the lighting is helpful for collision avoidance.

The red lights are helpful, but the white strobes can be even better for visibility.

When I am flying very low to the ground I am far more concerned about towers and windmills (or occasionally high tension power lines) than buildings. Fortunately all of my really low flying for work is done during daylight hours, but in heavy overcast or other low-light conditions the lights are very helpful.

Most tall buildings are in congested areas and most flight operations will be required to maintain an altitude of 1000 feet or more above such structures. The presence of towers in excess of 500 feet, and especially in excess of 1000 feet, in uncongested areas posses a much more credible threat to VFR low level flight.

The FAA describes the standards for structure and tower lighting in AC70/7460-1L. Generally, any structure that exceeds 200 ft AGL should be marked and/or lighted.

Note that, though the lighting may be mandatory, it may be NOTAMed out of service. For example:

!SFF 02/009 SFF OBST TOWER LGT (ASR 1060807) 473535.00N1171750.00W (5.5NM S SFF) 3971.1FT (352.4FT AGL) OUT OF SERVICE

  • $\begingroup$ Could you unpack or link “NOTAMed out of service” for the novices among the readers? $\endgroup$ Commented Feb 26, 2016 at 18:22
  • $\begingroup$ @sevensideddie Good idea, standby. $\endgroup$
    – J W
    Commented Feb 26, 2016 at 18:34
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    $\begingroup$ NOTAM stands for "NOtice To AirMen", and is an official notice filed with the local, regional, or national aviation authority to alert pilots of hazards or other deviations from normal protocols along their flight path. $\endgroup$ Commented Feb 26, 2016 at 18:50

Before the lights were installed, this happened...

enter image description here enter image description here (second picture via Pinterest)

A better picture of this incident (a 1915 Sopwith Baby at Horsea Island in 1917) appears in the front of the 1925 edition of the "Admiralty Handbook of Wireless Telegraphy" in a slightly snarky advert, captioned "A proof of the quality of Elwell masts".

  • $\begingroup$ Also, in NYC this happened. $\endgroup$
    – FreeMan
    Commented Feb 26, 2016 at 13:47

To answer your question directly, no, they are not used to indicate that you are too close to the ground. Some of them are over 1500 feet high.

They are used so you do not fly into them for obvious reasons or fly too close to them for less obvious reasons:

  1. Some are powerful transmitters and can interfere with the systems on the aircraft.
  2. Towers often have support wires which extend a long way from the obstacle with the light and do not have lights themselves.

Too close to the ground is figured out by looking; by the altimeter; by charts and by planning.

The red light just means "keep away!"

Some incidents and analysis of interference and even crashes attributed to high intensity EMR.

Some follow up on the Blackhawk crashes.

Whilst this paper focusses primarily on the ability of high powered EMR sources to cause ignition sparks up to 30kms away (!), it also shows how dangerous they are up to hundreds of metres away.

If anyone remains unconvinced that powerful transmitters need to be avoided by aircraft, please let me know and I'll do some more digging, but for now, I have an "all nighter" I need to pull to deliver a project tomorrow so I may be some time....

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    $\begingroup$ "Some of them are over a kilometre high." I have never heard of an obstacle over a kilometre tall. The world's tallest antenna is only 600m tall. $\endgroup$
    – abelenky
    Commented Feb 25, 2016 at 18:38
  • $\begingroup$ Some are powerful transmitters and can interfere with the systems on the aircraft. Has this ever been documented to occur? $\endgroup$
    – TomMcW
    Commented Feb 25, 2016 at 18:53
  • $\begingroup$ Personally, I have flown quite close to some of the transmitters (I don't know how powerful though) without any negative impact to aircraft systems. Such proximity would only be possible in VFR flight, where any possible system impact would be negligible for safety of flight. $\endgroup$
    – J W
    Commented Feb 25, 2016 at 19:28
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    $\begingroup$ A "drive by downvote" with no comment. I couldn't care less that I've lost a whole 2 rep points, but it really grates me that I can learn nothing from it. $\endgroup$
    – Simon
    Commented Feb 25, 2016 at 20:01
  • $\begingroup$ @abelenky Sorry, a simple typo which I fixed at the same time you where typing your comment. $\endgroup$
    – Simon
    Commented Feb 25, 2016 at 20:01

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