Originally Posted by Section 107

i live near IAD and have recently seen a few planes in the approach pattern with their landing lights (it looks like in the nose gear - they are too close together to be on the wings) in an alternating flashing pattern - like the lights on a school zone sign or school bus.

What is the significance of this? Its not all planes and since its at night I havent been able to determine the actual plane type or airline.

thanks