Kilauea Volcano
Kilauea is an active vulcano. In 1983 an eruption started and you will only see the volcano erupt in Flight Simulator on that year.

Change the time to a night of year 1983. Takeoff from Hilo Intl airport (PHTO), climb and maintain 5000 ft, and fly heading 204 for 23 nm. Return to PHTO on VOR 116.90.

Fireworks
Some national holidays in FSX are also celebrated with fireworks. The fireworks are animated and have sound effects.

For these to work, make sure that you have the special effects bar set all the way to the right.

New Year
Fly over a major city as the year changes, not sure if this could cause a malfunction as I have never tried it, but be careful.

Independence Day
The 4th of July is the American national holiday, Independence Day. There are fireworks in New York City, Washington, D.C., and Las Vegas from 22.00.

Bastille Day
The 14th of July is the French national holiday, Bastille Day. There are fireworks in Paris close to the Eiffel Tower from 22.00.