The Federal Aviation Administration (FAA) said Friday it is proposing a $777,000 civil penalty against Horizon Air for allegedly operating 32 Bombardier Q400 turboprop aircraft on nearly 50,000 flights without completing all required tests on new wing lighting systems.

In a letter sent to the airline Nov. 4, the FAA states that task cards prepared by Horizon personnel providing instructions for mechanics who installed pulsing lights on the wings failed to include a requirement to conduct tests for radio frequency and electromagnetic interference.

Because those tests were omitted, the aircraft were not in compliance with federal aviation regulations when subsequently returned to service.

Horizon spokeswoman Marianne Lindsey said the information on the task cards was based on the installation instructions from the manufacturer of the lighting system, Precise Flight of Bend, Ore.

The airline flew the aircraft between Oct. 19, 2009 and Mar. 17, 2010, before the FAA discovered the compliance problems during routine inspections. The FAA said Horizon immediately completed tests and inspections of all 32 aircraft before further flights.

Lindsey said the inspections showed that all the lights were functioning properly.

Horizon has 30 days to respond to the FAA's proposal to fine the airline.

"We're working with the FAA to resolve it," said Lindsey.

Dominic Gates: 206-464-2963 or dgates@seattletimes.com