Light arcs: wing nav lights show through 110°, the tail light through 70°. Green is starboard, red is port. "Red to red is safe."
Right-of-way order: balloon > glider > airship > powered. Powered gives way to everything, and everyone gives way to an aircraft towing.
Head-on:both turn right (not just one).
VFR low-level Class G: at/below 3,000 ft, ≤140 kt, by day → 1,500 m, clear of cloud, in sight of surface (the table's default is 5 km; 1,500 m is the speed/traffic concession).
The 8 km / 5 km split: 8 km visibility at or above FL100, 5 km below it.
Transition altitude is 3,000 ft in most of the UK (18,000 ft in the USA, don't import it).
High to low, beware below applies to falling temperature as well as falling pressure.
QFE vs QNH: QFE → height above the aerodrome; QNH → altitude above MSL.
Oxygen: crew above 10,000 ft for >30 min, or any time above 13,000 ft; passengers above 13,000 ft.
90-day rule:3 take-offs and landings to carry passengers; at least one at night to carry them at night.
Class 2 medical: validity 60 / 24 / 12 months for ages <40 / 40–49 / ≥50, truncated at 42 and 51.
Steady red light in flight = continue circling, do not land (not "stop", that's the on-ground meaning).
Transponder: 75 hijack, 76 radio fail, 77 emergency, 7000 conspicuity.
Notification-delay figure:45 min (aerodrome) and 30 min (SAR), read the question's context.
Empty mass includes unusable fuel and undrainable oil but excludes usable fuel, drainable oil and the crew.