At what distance would you begin to see the sequenced flashing strobe on an approach light system at night? 10 NM? 20 NM? Visibility plays a role, but consider CAVU.

Also, strobe lights on radio and cell towers, what is their visibility distance at night?

And at those distances, are they initially faint as they fade into view?

  • $\begingroup$ Isn't that the visibility part of a weather statement, i.e. visibility 5 miles means you can start to see the identification lights at 5 miles? $\endgroup$ – CGCampbell Aug 18 '14 at 19:56
  • $\begingroup$ requirements that I found all mention only candelas required (in the order of 270k in the day and 2k during the night) $\endgroup$ – ratchet freak Aug 18 '14 at 20:24
  • $\begingroup$ also relevant wiki page (no refs though) $\endgroup$ – ratchet freak Aug 18 '14 at 20:24
  • $\begingroup$ I think you are assuming that the airplane is approaching the lights at the optimum angle. In fact, the approach lights are highly directional. While a passenger in a GA plane, we crossed the final approach path to runway 6 at KISP (a Class C airport) and the lights went from not visible, to visible, to not visible in a very short time. So even though you know the optimal visibility, remember that it may be a lot less or zero if you are not in the best spot... $\endgroup$ – Skip Miller Aug 18 '14 at 22:48
  • $\begingroup$ @CGCampbell: I believe only runway visual range (RVR) is defined that way. And it is often larger than reported visibility. $\endgroup$ – Jan Hudec Aug 19 '14 at 7:51

For cell towers the FAA wants them to be visible for pilots in time for them to avoid them.

Pilots of aircraft travelling at 165 knots (190 mph/306kph) or less should be able to see obstruction lights in sufficient time to avoid the structure by at least 2,000 feet (610m) horizontally under all conditions of operation, provided the pilot is operating in accordance with FAR Part 91. Pilots operating between 165 knots (190 mph/303 km/h) and 250 knots (288 mph/463 kph) should be able to see the obstruction lights unless the weather deteriorates to 3 statute miles (4.8 kilometers) visibility at night, during which time period 2,000 candelas would be required to see the lights at 1.2 statute miles (1.9km). A higher intensity, with 3 statute miles (4.8 kilometers) visibility at night, could generate a residential annoyance factor. In addition, aircraft in these speed ranges can normally be expected to operate under instrument flight rules (IFR) at night when the visibility is 1 statute mile (1.6 kilometers).

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2070%207460-1K.pdf (page 63)


Flying through Central Valley of California at night I have seen runway light from many miles away. Probably 20nm+. The valley is low and flat with with a lot of airport in low population areas. As a result the runway lights in general, and approach lights in particular really stand out. Conversely when you are in a highly populated area (ex. Southern California) while the light travels as far, but you may have trouble picking up the runway environment out of the sea of lights. So having slant visibility does not necessarily equate to "seeing" the airport.


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