Wikipedia:Reference desk/Archives/Science/2019 June 24

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June 24

Are the blinking lights at the top and bottom of a Boeing 747 shown correctly?

Hi! I redrew the left image below as an animated SVG for the navigation lights article. Instead of a generic plane, I decided to use a Boeing 747 as it's common and there is an existing 3-view line drawing of it in Commons. I could identify in the article all the lights in the original except the ones on top of and below the fuselage. What are those? I drew them at arbitrary positions on the 747. Where should they go? Thanks, cmɢʟee⎆τaʟκ 23:57, 24 June 2019 (UTC)

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This is a great question!

On technicality, you have drawn three different types of lights: the position lights, the beacon, and the anticollision light system. These terms are described, e.g., in 14 C.F.R. 91.209 "Aircraft Lights". Even more excruciating regulatory detail for Transport Category Aircraft can be found in 14 CFR Part 25 Subpart F §1381 Lighting, defining permissible light viewing angles and so on.

For a Boeing 747, the standard lighting placement actually depends on when (e.g. what year) the specific aircraft was built, and whether the standard lights were used. As described in this 2018 article in Boeing Innovation Quarterly, A History of Boeing Commercial Transport Flight Deck Lighting and Display Optics Innovation, a modern 747 uses LED-based lighting. Of course, after the aircraft is sold, the customer can technically move or refurbish the exterior lighting - and since there are so many aircrafts flying in so many variations, operating in different roles in so many different places, it's a sure bet that at least a few have some non-standard exterior lighting variations.

You can get official CAD 3-views from Boeing for the 747: Airplane Characteristics for Airport Planning. Self-evidently, the "747" model refers to multiple different airframe types with slightly different shapes, profiles, and variations in the "minor-engineering-details."

You can also browse a huge selection of photographs of different airframes from many angles at JetPhotos.com, an enthusiast website. For example, here is a lovely evening photo with the "top red light" illuminated on one of my very favorite 747 airframes, N747NA, who is of course SOFIA. Here's a nice evening shot of Lufthansa 747-830 D-ABYM with both top and bottom red lights shining, and the same aircraft with its rear strobe showing.

And here is even more regulatory guidance in the form of AC 20-30B Aircraft Position Light and Anticollision Light Installations, from FAA.

As a side-note - you have not drawn the landing light, the taxi light, nor any of the "dome" lighting on the aircraft that is used to illuminate the ramp during loading and ground handling.

In short summary - you have drawn the bottom light too far back: that light would normally go on the "flat" part, forward of the landing gear bays and should be colored Aviation Red; but this is just a minor detail, and you might possibly find subtle variations on real aircraft out in the wild.

Nimur (talk) 10:23, 25 June 2019 (UTC)

Thank you very much, @Nimur:. I thought the landing, taxi and dome lights are used only on or near the ground, or do they leave them on in cruise? I'll update the other lights as you suggested. Cheers, cmɢʟee⎆τaʟκ 23:32, 30 June 2019 (UTC)

It would be very uncommon to use the landing, taxi and dome lights during cruise on a 747.

But while we're on the topic - for general aviation, (and for commercial or airline operators that want to participate), the FAA has an ongoing campaign, "Operation Lights On," to encourage landing-light operation during all phases of flight. More on this topic can be found in the AIM 4-3-23 Use of Aircraft Lights, and in Advisory Circular 90-48. Of course, this kind of thing is a trade-off between lightbulb lifetime and the ostensible safety improvement of using the light.

Operators of a big jet like a 747 are probably "a little less likely" to burn their landing light during all phases of flight - especially when the gear's up - but anything's possible.

Nimur (talk) 04:46, 1 July 2019 (UTC)