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We frequently holiday in Mallorca and more often than not see a strange light display on the odd airliner coming overhead, This is something like 2 octagonal light formations on the underside of the aircraft. Does anyone know anything about this?

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closed as off-topic by hippietrail, Mark Mayo, Karlson, VMAtm, Dirty-flow Oct 22 '13 at 15:12

  • This question does not appear to be about traveling within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

This question appears to be off-topic because it is about aviation or observing aircraft, not about traveling in them or otherwise relevant to travelers. – hippietrail Oct 22 '13 at 11:58

Any aircraft must have these lighting systems:

  • Navigation lights: red on the left wing tip and green on the right wing tip. Other aircraft or ATCs can determine the direction by looking at those.
  • Strobe lights: a strong flashing light to help aircraft avoid collisions in low visibility conditions.
  • Landing lights: if the aircraft is certified for night landings it must have landing lights which are strong lights at the forward usually to help pilots see terrain and runways.
  • Logo lights: usually at the tail to show the airlines logo at night, sometimes at the belly of the aircraft (as in A380).
  • Wing lights: to help pilots do their ground checks and to increase visibility in general.
  • Rotating beacons: usually used on ground to let ground personnel know that engines are running.

Now what you saw must be a combination of all of the above. Some aircraft look like a moving party at night, I remember the MD90s for example having a funny lights system if all lights are on.

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The "beacons" are NOT optional, and are the only lights that must be operational during daytime flight (others are only required at night, although may be used during the day). There are two beacon lights (one on top, one on the bottom), and they are sometimes referred to as the "operating" lights as they are turned on before the first engine is started, and not turned off until all engines are stopped. – Doc Oct 20 '13 at 7:32
@HaLaBi they are not optional compared to anything. Only aircraft lacking them are those either without engines or military (when a lot of rules are relaxed, and even then they usually have them, they just keep them off). Wing lights ever more double as logo lights for winglets too, so nice for the passengers to be able to see the airline logo on those while flying at night, so they know what airline they're flying with :() – jwenting Oct 21 '13 at 8:48
@HaLaBi it still said they were optional at the time I wrote that. I see it's now changed to remove that. Might want to move the paragraph about beacons to the required list to make it completely clear they're in fact required. – jwenting Oct 21 '13 at 11:08

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