I live in Portland,Oregon. I watched a large jetliner coming into the airspace heading to the airport. The red,green and tail lights were normal. But the headlights were blinking alternately. I have never seen that in all my years watching the sky. Is there a reason for the alternate blinking?Emergency onboard?
Some modern landing lights have a pulsating or alternating mode. It's just for being recognized more easily, has nothing to do with an emergency.
A constant white light heading right for you over a city full of lights doesn't get as much attention as a pulsating light which gets bigger each time as you get closer :)
Here is one example: https://www.preciseflight.com/pulselite-pulsing-aircraft-lights/
and their video: