Questions from the Cockpit: Night and day

Mack, a student pilot in Florida, writes: I just learned that there are three different definitions of night in the regulations! What’s the deal with all these overlapping definitions? Is the FAA just trying to make it harder on students than it needs to be?

It sometimes feels like the system is rigged, but there’s usually some method to the madness and I find that to be true for the overlapping night definitions, even though it’s not — pardon the pun — clear as night and day.

Who would have thought that something as simple as night and day could become so complex? This is why no one is “born” a pilot. There is so much to learn!

But first, for a refresher to the older pilots, and as an introduction to the newer pilots, “night” currently has three different definitions in the regulations. There’s one type of night for turning on your airplane’s position lights, one type of night for logging night flight, and yet another type of night for the proficiency requirements of carrying passengers at night.

What are they and why are they different?

We’ll dig into that, after a quick tip for student pilots: Section 1 of the regulations is a little dictionary that provides the foundational definitions of terms used throughout the regs. However, sometimes a given section will use a different definition, and those are usually found at the very front of the section in question.

But just to keep you on your toes, sometimes a stray reg will have its own independent little definition — and that is often the case when it comes to aviation night ops.

Oh, right, and then sometimes we have to go completely outside the regs to get a definition of a word used in the regs, which is also the case with night ops.

So, starting at the bottom, the §1.1 baseline definition of night is not at all what you might expect, at least not in normal citizen experience. Here night is defined as “the time between the end of evening civil twilight and the beginning of morning civil twilight.”

This definition then helpfully points out that these end and beginning times are published in the Air Almanac, but must be converted to local time.

The Air Almanac is a publication of the Astronomical Applications Department of the United States Naval Observatory. Ironically, given the title, it doesn’t have much to do with “air,” as we pilots think of it, at all. Instead, it’s a massive collection of data-heavy tables and charts used for celestial-based navigation. Now only available in a PDF, it’s a mind-boggling 909 pages long.

Luckily for us, you can also find local civil twilight end and beginning times in ForeFlight, and at websites like Weather Underground.

If you want to impress your examiner, know that the end or beginning of civil twilight is when the geometric center of the sun is 6° below the horizon. At this point it’s quite dim, but not fully dark.

As a rule of thumb, evening civil twilight ends about a half an hour after sunset and morning civil twilight begins about a half an hour before sunrise.

To be clear, the 6° measurement marks the stop/start times; civil twilight itself is the time slot between these points and the actual sunset or sunrise.

For pilots, the civil twilight end and start times are the bookends for logging night flight.

They also mark the time period when an airplane must meet the night equipment requirements of the back half of the “flaming tomato” regulation of §91.205 (c).

And lastly, for sport pilots, the twilights serve as the start-stop points of the operational day, as sport pilots don’t currently have night privileges. This will change — a bit — in October 2025 when sport pilots who choose to get a medical certificate will be able to earn a night-flight endorsement.

By the way, there are actually three different “official” twilights.

In addition to aviation’s civil twilight, there’s also nautical twilight and astronomical twilight, both of which are “darker.”

With nautical twilight, the center of the sun is 12° below the horizon, stars show, but the horizon can still barely be made out so that you can use a sextant for navigation. With astronomical twilight, the center of the sun is 18° down and it’s properly good and dark for astronomy.

Next, moving to aircraft lights, §91.209 says you have to use your position lights — with a few exceptions for Alaska — not between civil twilights, but between sunset and sunrise instead.

Which begs the question: How is something as simple as sunset or sunrise defined by the FAA? How much of the disc of the sun needs to be above or below the horizon?

For that, you need to turn to the Aeronautical Information Manual (AIM), where the answer is hidden in the Helicopter Operations section, which most fixed-wing pilots never read.

In 10-2-2 (b) (c) we are told sun set or rise is when “the upper edge of the disc of the sun is on the horizon.”

At least that’s pretty logical and straightforward. For preflight planning, sunset and sunrise times are widely published in EFBs, on weather websites, and in weather apps. Reminder: They change daily for any given location.

Meanwhile, when it comes to carrying passengers at night, §61.57 (b) says you can’t carry a passenger between the periods of one hour after sunset to one hour before sunrise, unless you’ve done three takeoffs and landings to a full stop in the same “night” conditions in the previous 90 days. An hour after and an hour before it is well and truly dark.

OK, in reviewing all of this, I’m beginning to understand why this is a bit much for the new student.

But all of that was simply the what, not the why.

So…why?

The first thing to consider is that in early aviation, night flight wasn’t really a thing, beyond some early night exhibition flying, so the regulations probably evolved in a somewhat jerky fashion.

In the 1941 regulations, the Naval Observatory was used, as it is today, but the baseline definition of night was different. Back then, night was sunset to sunrise, with no mention of twilight, so things have changed over the years. Then, like today, you were to turn your lights on when the sun set. This made sense, as if the sun has set over the land, it’s harder to spot other airplanes, and it sure would be nice to see anyone else who’s up there with you.

And, like today, back in the 1940s there was the rule about night proficiency for carrying passengers, using the same “night” definition of an hour after/hour before that we use today, with the only difference being that instead of three takeoffs and landings in the previous 90 days, you had to do five.

This rule has some logic, too, as at sunset it’s still pretty bright — and it makes sense for pilots to have actual experience with landing in the dark before exposing the public to it.

So the lights on and passenger carrying “nights” have been with us — pretty much unchanged — for a long time. But when did the base definition for logging time and equipment change from sunset/sunrise to twilight?

I’ve been unable, so far, to determine when civil twilight first came into the picture for aviation regulations. But, again, there is some logic to it.

I mean, it’s not really “night” right after the sun sets. There is plenty of light for what used to be called “contact flying,” what we now call VFR. To log night flight, logically, it should really be a bit darker.

And while I understand that it’s maddening to memorize for the new student, I do find some (only slightly) twisted logic to lights on at sunset, not logging night flight until it’s getting pretty dim, and no passenger carrying in the dark without recency of experience.

So I don’t think the FAA is really out to make things more difficult for the student, but rather, has created situationally flexible regulations — at least, when it comes to day and night.

But you might just have a case when it comes to the overlapping definitions of cross-country flight, because there are seven different definitions of what a cross-country flight is and what a cross-country flight isn’t.

But that’s a subject for another day…or night.