Mike the Strike wrote:
"IGC flight logs contain a GPS time stamp which is the most exact time
standard readily available. So, violations of this requirement are
quite plain to see in these logs."

Unfortunately, sunset doesn't come with a GPS timestamp, so I'm afraid
this isn't as easy as you make it sound.

Yes, I know there are standard tables of sunset times, but these make
assumptions that may not be exactly correct and at a given location
actual sunset may differ from the calculated one by many minutes.
(Ask any local physicist./astronomer).

Of course, gross violations are pretty obvious, but I have operated
from a field where landing to the west is best done after the sun has
descended behind mountains, which usually occurs close to the time of
"official" sunset and is standard practice by those flying late.

Methinks all this scrutiny of flight logs is getting a bit too
intrusive and nit-picky.

Mike

The apparent movement of the sun in the sky is known very precisely (we
have been observing the sun for centuries). The only variable is the
refraction of the atmosphere, which changes the precise angle at which
the sun appears to pass below the local horizon. Various sunset
calculations use different refraction calculations, so they may differ
by a few minutes, but not "many minutes". The time of actual sunset may
also vary by a few minutes from the calculated value. The US Naval
Observatory has a sunrise/sunset calculator available online, and this
is probably the most reliable source for sunset times.

Unfortunately there is widespread ignorance of the sunset rule for
aircraft lighting, despite the fact that it has remained unchanged for
many years--longer than most pilots have been flying. So, we have seen
a few gross violations posted to OLC.

The point of all this is to get pilots to self-police, and not post
these flights in the first place. They should not be making flights
that continue after sunset witout lights anyway, but we certainly don't
want to see them on the OLC in any case.

P.S. The sun will appear to set below mountains before official sunset
when at an altitude lower than the mountains, becase the mountains will
appear to project above the local horizon.

P.P.S. Note that the sun will appear to set later than official sunset
when flying for the opposite reason--the local horizon appears to be
depressed. So you will need to enter the pattern to land well before
the sun appears to be setting in flight.