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Is it permissible for an aircraft to fly without red, green, and white strobe position lights?

Is it possible for any aircraft to legally fly with only a solid white or solid red light on the underbelly?

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    $\begingroup$ The use of the words "navigation beacons" is going to cause confusion. I think you are referring to the position lights. If so, I'd clarify that language. $\endgroup$ – ryan1618 Oct 5 '15 at 1:56
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    $\begingroup$ Secret goverment/military aircraft. $\endgroup$ – Simon Oct 5 '15 at 6:07
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    $\begingroup$ All gliders fly without position lights. So the answer must be Yes, even if no external light is fitted. $\endgroup$ – Peter Kämpf Oct 5 '15 at 16:12
  • $\begingroup$ Yes, during the day. Lights are required only for night or IMC flying, and a lot of ultralights and LSAs intended for day VFR only therefore do not bother. $\endgroup$ – KeithS Oct 5 '15 at 17:03
  • $\begingroup$ I recently witnessed a V type lighting configuration of one solid red, and two solid white lights. It was night so I'm unsure if it was 1 or 3 aircraft, but my gut tells me it was 3 flying in formation. $\endgroup$ – Styler Oct 5 '15 at 22:19
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This answer assumes that the question is in the context of the FAA's jurisdiction.

The red, green and white lights are position lights. They are required from sunset to sunrise by 14 CFR 91.203.

(a) During the period from sunset to sunrise (or, in Alaska, during the period a prominent unlighted object cannot be seen from a distance of 3 statute miles or the sun is more than 6 degrees below the horizon)—

...

(1) Operate an aircraft unless it has lighted position lights;

A solid red or solid white light on the underbelly doesn't correspond to a configuration that I am familiar with and doesn't meet the legal requirements.

I have, however, seen some older varieties of rotating beacons that if broken may become a solid red light mounted on the underbelly. Some older models actually have a motor that actuates rotation. If one had a failed motor it could appear as a solid red light.

rotating beacon

The strobes are anticollision lights. The answer is also in 14 CFR 91.203 . If anticollision lights are installed, they must be used unless the pilot turns them off in the interest of safety. The most common reason for this is if the aircraft is flying in the clouds and the diffuse strobing lights are a distraction or cause of disorientation such as flicker vertigo.

(a) During the period from sunset to sunrise (or, in Alaska, during the period a prominent unlighted object cannot be seen from a distance of 3 statute miles or the sun is more than 6 degrees below the horizon)—

...

(b) Operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights. However, the anticollision lights need not be lighted when the pilot-in-command determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.

14 CFR 91.205 is also relevant. Parts of it deal with the FAA requirements for both position and anticollision light systems. It states that aircraft may not be operated without position lights. It also states that aircraft may not be operated without anticollision lights installed with some exceptions.

There are some provisions by which a flight may be conducted legally with broken lights so that it may be repaired. One such provision is also found in 14 CFR 91.205.

(11) For small civil airplanes certificated after March 11, 1996, in accordance with part 23 of this chapter, an approved aviation red or aviation white anticollision light system. In the event of failure of any light of the anticollision light system, operation of the aircraft may continue to a location where repairs or replacement can be made.

If you're really interested, and I mean really really interested, the FAA released AC 20-74 which contains a lot of technical data on exactly how these lights are to be built in terms of intensity, color and position. Delving into this document should be reserved for the truly bored and those who manufacture aircraft lighting.

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I'm not sure if aircraft has any navigational beacon.

The red and white (strobe) lights are anti collision lights.

According to Aeronautical Information Manual(AIM), 4−3−23. Use of Aircraft Lights,

An aircraft anti−collision light system can use one or more rotating beacons and/or strobe lights, be colored either red or white, and have different (higher than minimum) intensities when compared to other aircraft. Many aircraft have both a rotating beacon and a strobe light system.

Usually, the anti-collision/position lights are to be operated during night flying. From the same manual:

Aircraft position lights are required to be lighted on aircraft operated on the surface and in flight from sunset to sunrise. In addition, aircraft equipped with an anti−collision light system are required to operate that light system during all types of operations

However, the pilot can turn them off if there are safety concerns.

However, during any adverse meteorological conditions, the pilot−in−command may determine that the anti−collision lights should be turned off when their light output would constitute a hazard to safety

In your case, the pilot may have turned off the anti-collision lights and operated only the position lights.

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