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On the KLM website, I found this strange quote:

If planes pass each other at night they sometimes use light signals to say hello.

Is it true and common? How it is done (which lights/patterns)?

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    $\begingroup$ I wouldn't say that it would be common as if two aircraft are close enough to receive light signals, they would be in very close proximity of each other.. therefore posing a threat $\endgroup$ – FallenUser Jul 12 '18 at 13:08
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    $\begingroup$ I don't usually cruise with my landing and taxi lights on, but if I see another plane nearby around dusk (when my nav and beacon may not be bright enough to stand out against a bright sky, but the airplane fuselage may not be visible in the diminishing ambient light), I will turn on the rest of my lights to try to be more visible. I'm not saying "hello", I'm just trying to clarify my presence. $\endgroup$ – abelenky Jul 12 '18 at 13:15
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    $\begingroup$ You'd be surprised how far you can see in a clear sky @FallenUser, also keep in mind that 1000ft vertically is considered adequate separation under Reduced Vertical Separation Minimum regulations, which is plenty close. $\endgroup$ – GdD Jul 12 '18 at 13:18
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    $\begingroup$ @GdD Yes indeed I would and I would love to see how $\endgroup$ – FallenUser Jul 12 '18 at 14:24
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    $\begingroup$ @Glacomo Catenazzi: Did you mean the part in 'This is your captain speaking' where it says: 'If planes pass each other at night they sometimes use light signals to say hello.'? $\endgroup$ – FallenUser Jul 12 '18 at 14:26
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Yes, it is true. When two aircraft flying in opposite directions pass each other at night, it is quite common for one or both to briefly turn on their landings lights. This is done partially to "say hello", and also to increase situational awareness. I would guess it happens about 50% of the time.

Usually one aircraft will turn on their landing lights about 2-5 miles back and wait for the other to briefly flash their lights in response. It is not uncommon to get no response because the pilots on the other aircraft may have their heads down, and not see the other aircraft. Some pilots don't respond because they feel it is a useless practice, and can't be bothered.

When there is only 1,000' vertical separation of opposite direction, or crossing traffic, some ATC jurisdictions might require the controller to inform the aircraft of each other's presence. In that case it is more likely that both aircraft will turn on their landing lights to be more visible to the other aircraft. There is no operational requirement to do this, but most pilots tend to go along with this practice.

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    $\begingroup$ Wouldn't the airlines see each other on TCAS anyway? I have ADS-B In now, and I appreciate being able to see other nearby traffic and their height above me or below me, and the direction they are heading. I expect to see even more as Jan 1, 2020 comes around. (USA requirement for a lot, but not all, of the National Air System (NAS).) $\endgroup$ – CrossRoads Jul 12 '18 at 16:03
  • $\begingroup$ "When there is only 1,000' vertical separation of opposite direction, or crossing traffic, ATC rules usually require the controller to inform the aircraft" not true $\endgroup$ – J. Hougaard Jul 13 '18 at 14:07
  • $\begingroup$ @J.Hougaard I edited my answer to say “some ATC jurisdictions might require”. $\endgroup$ – Mike Sowsun Jul 13 '18 at 14:50
  • $\begingroup$ In my experience, this is what I see too. Some pilots do it, and some don't. $\endgroup$ – Lnafziger Jul 13 '18 at 14:54

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