How night and IFR time are calculated in a pilot logbook
Civil twilight, great-circle tracks, and what counts as IFR — how Aerolog computes night and instrument time, and when to override it.
Two columns cause more logbook confusion than any others: night time and IFR time. Both matter for licence renewal, currency, and job applications — and both are easy to get wrong if you round on the ramp. Here's how they're actually defined, and how Aerolog computes them.
What "night" actually means
Under ICAO — and under EASA and the FAA with minor wording changes — night is the period between the end of evening civil twilight and the beginning of morning civil twilight, computed at the aircraft's position. Civil twilight is when the geometric centre of the sun sits 6° below the horizon. It's not sunset; it's about 30 minutes later.
Why great-circle tracks matter
On a westbound sector, you're outrunning the sunset. On a polar leg, you might cross civil twilight three times. A logbook that just checks "did the aircraft depart after dark?" gets these wrong by a full hour. Aerolog samples points along the great-circle route between your departure and arrival and computes twilight at each one, then sums the night portion.
When you should override night time
If you took a significant reroute for weather, or if a diversion made the actual track meaningfully different from the great circle, edit the flight and enter the correct value. The computed number is a strong default, not a legal claim.
IFR time is trickier
IFR time is any portion of the flight conducted under instrument flight rules. In commercial airline flying, that's almost always the entire block time. In GA and instruction, it's the portion you actually flew on an IFR flight plan or in actual IMC.
Aerolog defaults to full-block IFR when the flight is filed IFR and the aircraft type is normally IFR-only (jets, most turboprops). For piston GA it defaults to zero and prompts you to enter the portion. You can always edit either value.
What about "instrument" time?
Some authorities separate "IFR time" (flown under the rules) from "instrument time" (actual + simulated IMC). Aerolog tracks both columns and exports them separately, so your PDF matches whichever authority you file with.
Bottom line
You don't need to compute these on the ramp. Log the block times accurately, let the app do the geometry, and correct the handful of flights where the model was wrong. That's a more honest logbook than anything hand-rounded.