Thanks for the tips, and to Nate Miller for the video! That jet’s low flyby over northwest West Seattle this past hour was courtesy of Boeing – Flightradar24 identifies it as the “ecoDemonstrator” jet, a 777-200ER with its underside painted with POWERED BY SAF – short for Sustainable Aviation Fuel. Here’s a closer look in a photo tweeted by Bill Schrier:
(The smaller plane accompanying it is not identified on the tracker – possibly for photography.) You can read about the ecoDemonstrator program on Boeing’s website.