St. Elmo's Fire is which phenomenon?

• A. A fuel discharge phenomenon
• B. A weather phenomenon involving lightning
• C. A corona discharge which lights up the aircraft surface areas where maximum static discharge occurs
• D. An electrical grounding procedure

Answer: (C)

Corona discharge from a high electrostatic field around a sharp part of the airplane produces St. Elmo’s Fire. The glow occurs because the strong electric field ionizes the surrounding air, creating a luminous corona that lights up the aircraft surfaces where the static charge is most intense—typically at tips, edges, or other pointed areas. It isn’t related to fuel discharge, it’s not actual lightning or a grounding procedure, and it doesn’t require a spark to ground; it’s a visual glow from ionized air. So the phenomenon is a corona discharge lighting the surface areas where maximum static discharge occurs.