Narrative:

We departed on a 91K flight. Climbing through around FL230; the first officer turned the rheostat that controls the cockpit map light that is found on the co-pilot's side-wall above the flight phone. The first officer told me he saw some small sparks when he turned the rheostat on and asked if I had seen them. I had not. I was unsure what exactly it could be (possibly just some static electricity?) and I wasn't sure exactly what he saw or exactly where he saw it other than what he described to me as small sparks near the cockpit side wall when he turned the rheostat as I was not looking when he turned it on. I have seen some rheostats on occasion make very small sparks when they are turned at times; so I asked him to turn it again so I could see exactly what he was seeing. When he turned the rheostat for the light on; there was a 'popping' sound (loud enough to be heard over the cockpit noise) and at least two large blue sparks that shot out from under the black part of the cockpit side wall almost to the metal ash tray on the co-pilot's side (it appeared that one spark went towards the top of the ashtray; another spark went towards the bottom of the ash tray and another spark connected the two). The distance from the rheostat to the ashtray is a good 6 inches or so. We were both very surprised to see this (the first officer said that was nothing like the small sparks he originally saw). We quickly made mention of landing as a precaution. There was no smoke or fumes and the first officer checked the area with the back of his hand to verify there wasn't any excessive heat...there was not. I asked the first officer for the flight phone so I could call the company and let them know what was going on. The first officer took over as the pilot flying and asked for ATC to level off our climb. I called up and spoke with the on-duty chief pilot and described to him our situation and he asked where we were and what we were going to do. As pilots; we hate to inconvenience the customers; but the first officer and I determined the safest and most conservative action would be to make a precautionary landing because we really had no idea what was going on with the wiring and didn't want to continue on into a situation that could have possibly deteriorated into a smoke or a fire situation. We told the chief pilot that we would land the aircraft. We conferenced in dispatch and determined that the weather was good at the nearby airport and there was plenty of runway available. By this time; we had informed ATC of our situation and requested a descent. ATC started us down. I resumed the pilot flying duties. We declared an emergency with ATC. Fuel remaining and souls on board were given to ATC. We briefed the passenger about the situation and he was very much in agreement with our decision to land. We were given a direct routing back to the airport and the visual approach. ATC rolled the emergency ground equipment as a precaution. The landing was uneventful and we taxied to the FBO ramp and shut down. There was no evacuation; but we did shut the aircraft down and have the crew and passenger deplane through the normal exit as soon as the aircraft was completely powered down. A representative from the airport fire department met the flight; as did an airport operations supervisor. They asked if everyone was okay and asked for a brief description of the situation. Looking back on the event; I felt we made the correct decision to land. While the flight would have likely continued on uneventfully to our destination; there was also the possibility that the small electrical problem could have turned into a major smoke or in-flight fire emergency. Landing at the nearest suitable airport was the most conservative decision and the safest course of action. If I were ever presented with a similar situation I would take the same action. The passenger was very understanding of the situation and was happy that we had made the choice to land when we told him what the problem was.

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Original NASA ASRS Text

Title: A BE400 crew reported a six inch electrical arc from the First Officer's sidewall to near the ash tray when the Map Light rheostat was turned. Following this event an emergency was declared and aircraft diverted to a nearby airport.

Narrative: We departed on a 91K flight. Climbing through around FL230; the First Officer turned the rheostat that controls the cockpit map light that is found on the co-pilot's side-wall above the flight phone. The First Officer told me he saw some small sparks when he turned the rheostat on and asked if I had seen them. I had not. I was unsure what exactly it could be (possibly just some static electricity?) and I wasn't sure exactly what he saw or exactly where he saw it other than what he described to me as small sparks near the cockpit side wall when he turned the rheostat as I was not looking when he turned it on. I have seen some rheostats on occasion make very small sparks when they are turned at times; so I asked him to turn it again so I could see exactly what he was seeing. When he turned the rheostat for the light on; there was a 'popping' sound (loud enough to be heard over the cockpit noise) and at least two large blue sparks that shot out from under the black part of the cockpit side wall almost to the metal ash tray on the co-pilot's side (it appeared that one spark went towards the top of the ashtray; another spark went towards the bottom of the ash tray and another spark connected the two). The distance from the rheostat to the ashtray is a good 6 inches or so. We were both very surprised to see this (The First Officer said that was nothing like the small sparks he originally saw). We quickly made mention of landing as a precaution. There was no smoke or fumes and the First Officer checked the area with the back of his hand to verify there wasn't any excessive heat...there was not. I asked the First Officer for the flight phone so I could call the Company and let them know what was going on. The First Officer took over as the pilot flying and asked for ATC to level off our climb. I called up and spoke with the on-duty Chief Pilot and described to him our situation and he asked where we were and what we were going to do. As pilots; we hate to inconvenience the customers; but the First Officer and I determined the safest and most conservative action would be to make a precautionary landing because we really had no idea what was going on with the wiring and didn't want to continue on into a situation that could have possibly deteriorated into a smoke or a fire situation. We told the Chief pilot that we would land the aircraft. We conferenced in Dispatch and determined that the weather was good at the nearby airport and there was plenty of runway available. By this time; we had informed ATC of our situation and requested a descent. ATC started us down. I resumed the pilot flying duties. We declared an emergency with ATC. Fuel remaining and souls on board were given to ATC. We briefed the passenger about the situation and he was very much in agreement with our decision to land. We were given a direct routing back to the airport and the visual approach. ATC rolled the emergency ground equipment as a precaution. The landing was uneventful and we taxied to the FBO ramp and shut down. There was no evacuation; but we did shut the aircraft down and have the crew and passenger deplane through the normal exit as soon as the aircraft was completely powered down. A Representative from the airport Fire Department met the flight; as did an Airport Operations Supervisor. They asked if everyone was okay and asked for a brief description of the situation. Looking back on the event; I felt we made the correct decision to land. While the flight would have likely continued on uneventfully to our destination; there was also the possibility that the small electrical problem could have turned into a major smoke or in-flight fire emergency. Landing at the nearest suitable airport was the most conservative decision and the safest course of action. If I were ever presented with a similar situation I would take the same action. The passenger was very understanding of the situation and was happy that we had made the choice to land when we told him what the problem was.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.