UFO formation sighted over Kent, Washington

Sitting in my car after having arrived home from work. Talking to my brother who lives about 4 blocks away on my cell phone. See some lights coming toward me and see that they are pulsating red lights. They are a formation of 6. Three are single file with the remaining three in a triangular formation. Very cold and clear night. Altitude of the formation is hard to discern. 3,000 ft or more. Moving from east to west. As formation moves directly overhead the lights start going out until only one remains. Formation headed in the direction of SeaTac International airport. I told my brother to go outside at the time I first saw them and he confirmed that he saw them too. This is the first time I had ever seen anything like that before. There was no sound heard from the craft. I am a pilot and know most aircraft lighting systems. This was something new.