Static discharges on an E-4B refueling from a KC-135.
The following video shows an interesting phenomenon. An E-4B Nightwatch National Airborne Command Post (NAOC) approaches a KC-135 in cloudy weather and the differential static equalization between the two aircraft creates static discharges that are clearly visible.
Once the boom touches the receptacle of the E-4 the charges are equalized and the static stops. “What you really cannot see in this video is the semi-transparent shaft of purplish/pink electrons moving between the two aircraft, this is commonly known as St Elmo’s Fire,” says the uploader of the video on YT.
St. Elmo’s fire is a weather-induced phenomenon in which luminous plasma is created by a corona discharge from a sharp or pointed object in a strong electric field in the atmosphere: it appears every now and then on the cockpits of aircraft flying through the clouds or not far from thunderstorms.
This phenomenon is not dangerous to the aircraft: the plane is shielded by Faraday Cage, that blocks out external static electrical fields and charges redistribute on the conducting material without affecting the cage’s interior.
The E-4B, designed to carry the U.S. SecDef as well as other U.S. top officials, is specifically designed to keep American decision makers alive in case of nuclear wars, zombie invasions or alien attacks. Therefore, it has to be able to fly through any EMP (electromagnetic pulse) with unharmed systems. That’s why this highly modified Boeing 747 does not feature modern glass cockpit: old-fashioned, analogue-style avionics are more resistant to EMPs.