The Calgary Airport Authority is trying to figure out why a backup system didn't kick in properly after a power outage on Saturday night that forced planes to circle overhead or redirect to other airports.

The incident happened about the same time as Earth Hour, when people were asked to turn out the lights to save energy, but was unrelated, according to officials.

The outage shut down airfield lighting for an hour.

Spokeswoman Jody Moseley said the initial outage was caused by a problem with Enmax somewhere off airport property, but that the airport's backup system failed.

"Our backup systems did not perform the way they should have," said Moseley.

"They did engage quickly, but unfortunately we did experience some difficulty in keeping them up and running, which is why for safety reasons ... it resulted in not having any departures or arrivals of aircraft during that time."

The airport authority is now investigating what happened to the backup system.

Moseley said the fact the outage occurred around the same time as Earth Hour was strictly a coincidence, and while the airport shut off unnecessary lights inside the terminal for the hour, the runway lighting never went out.