Day VFR -- when is it night?

[3Dreaming]

When you have a set time in the morning that you can take off I see no problem with taking off as soon as that time is past. In other word there is no need for a safety buffer there.
I also see no problem with recomending that you plan a landing at sunset, as long as the student is taught the limit is the end of evening civil twilight. If you are a local flight I see no problem with flying into this time period.

As an instructor sometimes we need to set limits with more safety margin than the regulations for our students, but we also need to teach the regulatory limits too.

Jim, for student cross country flight would you let them go with 3 miles visibility? I don't think there are many students I would send out in conditions like that.

[jnmeade]

No, I would not send students on a cross country with 3 miles vis. I can think of very few times I'd fly with 3 miles vis. I would be reluctant to fly with 5 miles vis even in a slow plane.

[drseti]

Well, Jim, then we're pretty much in agreement. We teach the FARs, make sure our students know the legal limits, and then set personal or company limits that are more conservative.

[CharlieTango]

Would you allow a solo student to fly in crosswinds right up to the demonstrated maximum in the POH?

or

3 mile visibility

Those are equally poor analogies, Jim's point is valid, skill / safety related personal limitations and the law of primacy need not be mutually exclusive.

[3Dreaming]

Jim, like I said I agree that there is no reason to not be able to take off at 1 minute after the begining of morning civil twilight. If you accidentally take off a little later there is no problem. Where do you set the limit as an instructor for a student to be on the ground by? Do you think you should let them to fly right up to the end of evening civil twilight? What if you have to make a go around and are now beyond civil twilight?

[jnmeade]

Where do you set the limit as an instructor for a student to be on the ground by? Do you think you should let them to fly right up to the end of evening civil twilight? What if you have to make a go around and are now beyond civil twilight?

Here is a definition from the US Naval Observatory

"Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities.

Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is geometrically 12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other illumination, general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible. During nautical twilight the illumination level is such that the horizon is still visible even on a Moonless night allowing mariners to take reliable star sights for navigational purposes, hence the name."

Several issues come to mind:
Local atmospheric conditions can significantly affect visibility and should be taken into account.
Landing after the end of civil twilight means the pilot has fewer visual cues to work with. Some instruction in flight with reference to instruments may be useful (as is already required for faster LSA pilots before a solo cross country).
A local, quiet, non-towered airport may have fewer interruptions that would extend a flight into nautical twilight.
The CFI should have provided some training during the civil twilight period, including landing with no runway lights and no landing light and no cockpit lights.

In my experience, at a quiet airport, one can do a pattern circuit in about 0.1 hours. If it was a nice evening with no traffic, I'd tell my student to not start a pattern with less than 15 minutes before the end of civil twilight. I think that gives the well-trained student enough time to make one missed approach and still land before the end of civil twilight. If one had to execute a go around for good cause and extended into nautical twilight, I would not be afraid to defend it to the FAA, especially if it was an outside event such as someone pulled onto the runway.

[jnmeade]

Well, Jim, then we're pretty much in agreement. We teach the FARs, make sure our students know the legal limits, and then set personal or company limits that are more conservative.

My objection was that you didn't make any point of teaching the FARs, you just set a company policy.

Plus, you set limits that I thought were arbitrary, such as no take off before sunrise when a take-off after the beginning of morning civil twilight was perfectly legal, assuming there were adequate atmospheric conditions and the student was trained.

If one chooses to not teach students flight during civil twilight, I can see where the CFI would not sign off the student for such flight. I think it is wrong to not provide such teaching, since the student can exercise the privilege as soon as they have their certificate.

[drseti]

In all due respect, Jim, since I didn't post a whole essay, you don't really know what I do or don't make a point of teaching. In this thread, I was only discussing company policy. But, if you're interested, my whole curriculum is posted to my website for all to see.

[jnmeade]

It's your forum, Paul, and you always win the arguments. You'd think I'd learn.

[drseti]

In my experience, at a quiet airport, one can do a pattern circuit in about 0.1 hours.

That seems a bit optimistic (not to mention rushed) to me, Jim. Let's say your pattern is 1000 AGL, and you both climb and descend at 500 FPM. You eat up four minutes getting to altitude and back down again. If your runway is a mile long, and you fly the pattern at 60 knots, you're going to have about a minute on the downwind at pattern altitude. That would only leave you one minute to taxi back (at waaaaay too much speed), and no time to critique the circuit before launching the next one. I like to plan for five or six circuits per hour, not ten (assuming full-stop landings. As an oldtime taildragger pilot, I don't use touch and goes so much).

If it was a nice evening with no traffic, I'd tell my student to not start a pattern with less than 15 minutes before the end of civil twilight.

.

Make that 20 minutes and I'm right there with you. Depending upon your latitude and season, that comes pretty close to my "stop at sunset" policy!

[drseti]

It's your forum, Paul, and you always win the arguments. You'd think I'd learn.

It's not about winning or losing, Jim, it's about exploring diverse viewpoints, and different teaching styles, and learning from each other. I've learned a thing or two from you over the years. I hope the converse is also true.

[FastEddieB]

It's your forum, Paul, and you always win the arguments. You'd think I'd learn.

Hey! Why do you think I always choose his side?

[drseti]

Back to the original topic: to underscore the effect of latitude, I ran some different locations. The difference between civil twilight and sunrise today was 33 minutes for Lock Haven, 26 minutes for Miami, 24 minutes for Honolulu, 40 minutes for Seattle, and 1 hour 12 minutes for Juneau! In the southern hemisphere this time of year, there's very little civil twilight. Likewise in the northern hemisphere in December.

[drseti]

Here is a definition from the US Naval Observatory.

I was remiss yesterday in not thanking you for posting that. Very clear and succinct, and speaks to the OP's question.

[deltafox]

What have I learned? The FARs set the boundaries. All pilots should know what these boundaries are and why they are there. Beyond that we have additional limitations, aircraft and pilot limitations among them. There are times when pilot limitations are more stringent than FARs (experience, or lack thereof) or more flexible (emergencies). But the good pilot must know the boundaries before he decides to amend them.

For a new CFI, this is good stuff. Thank you for this conversation.