Narrative:

At 11000 ft en route to ZZZ red avionic smoke illuminated from the cwp. After completing the memory items; I went to the QRH. After confirming the memory items were complete; we completed the next 2 tasks and upon reading the 'land at nearest suitable airport;' I informed center of the avionic smoke indication and I was planning on turning back to ZZZ1; ZZZ2 or the nearest airport. With oxygen mask on; ATC did not understand my radio call and asked me to repeat. Another flight radioed that I was reporting smoke in the cockpit. ATC informed me the 2 nearest airports were ZZZ3 and ZZZ4 at 20 mi and 30 mi away. I chose ZZZ4 because I was sure it had arff capability. In going through the QRH; we started to come to the conclusion that it might be an indication problem; but still was not sure. I called back to the flight attendant to see if she could or smell any smoke. She said no. With no odor or sign of smoke in the cockpit; I checked the avionics extinguisher hole to feel for heat and or smoke; I could not detect any. I was more convinced we did not have a fire but still felt the best course of action was to continue to ZZZ4 with the oxygen masks on in terms of safety. I reaffirmed with ZZZ4 tower we were an emergency aircraft and needed the trucks. Upon landing the aircraft was stopped and shut down and we deplaned the passenger without further incident. Callback conversation with reporter revealed the following information: the reporter stated that his air carrier's maintenance believed the avionics smoke detector failed and gave them a false warning. A great deal of incident review occurred following this event with the FAA; air carrier mgmt; union reps; pilot training department; and maintenance. The air carrier was not pleased that the captain diverted 30 NM short of its destination. The FAA and union appeared supportive because the aircraft is designed to immediately vent smoke overboard not allowing circulation in the aircraft interior. Because of this design feature and the fact that the crew had their smoke masks on they most probably would not have smelled the smoke. The crash fire rescue crew did not see smoke after landing but the captain elected to have the passenger exit the aircraft via a normal stair in order to err on the safe side. Supplemental information from acn 758510: en route red avionic smoke illumination on cwp and triple chime. Captain called for memory items; memory items completed and confirmed I monitored and flew the airplane per last ATC assignment; captain began QRH. I could not hear his instructions through my headset but could hear him faintly hear outside of equipment. He said check circuit breakers. I completed instruction and confirmed none tripped. Captain began communication of emergency with ATC. Captain completed QRH still poor communication between us at this time. I can not hear him. I can hear ATC. I continue to fly. Captain requests emergency landing at nearest suitable airport. We accept vectors to ZZZ4. Captain requests arff. I confirm. We have declared an emergency and need arff on scene. During this time flight attendant was notified of the diversion and was told this is for real. Flight attendant attempted to interrupt our duties several times. I responded during the third interruption to not respond to her as we were fully task saturated. Captain made request of flight attendant for fire or smoke detection. We had made attempts to detect fire or smoke and determined negative. Then we got oxygen warning light on cwp. I continued with ATC instruction for visual approach. We completed normal checklists for approach; descent; and final checks for landing. Supplemental information from acn 758512: during cruise I received a call from the flight deck indicating that the avionics smoke indicator light had illuminated in the cockpit. I was asked if I saw or smelled any smoke in the cabin. I checked the cabin as well as the area in the cabin where the avionics system is located behind the flight attendant jumpseat and saw; felt or smelled nothing and communicated that back to the flight deck. I was then informed that we would be diverting and making an emergency landing at ZZZ4 and to prepare the cabin for landing and to stand by for further evacuate/evacuation instructions should that be necessary. The landing was uneventful and crash fire rescue equipment met the aircraft. With no immediate threat present; we deplaned the aircraft in a normal fashion. Postflt -- evacuate/evacuation procedures were still followed in relation to the passenger.

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Original NASA ASRS Text

Title: AN S340 DIVERTED TO A NEARBY ARPT AFTER DECLARING AN EMER FOR A RED AVIONICS SMOKE WARNING.

Narrative: AT 11000 FT ENRTE TO ZZZ RED AVIONIC SMOKE ILLUMINATED FROM THE CWP. AFTER COMPLETING THE MEMORY ITEMS; I WENT TO THE QRH. AFTER CONFIRMING THE MEMORY ITEMS WERE COMPLETE; WE COMPLETED THE NEXT 2 TASKS AND UPON READING THE 'LAND AT NEAREST SUITABLE ARPT;' I INFORMED CTR OF THE AVIONIC SMOKE INDICATION AND I WAS PLANNING ON TURNING BACK TO ZZZ1; ZZZ2 OR THE NEAREST ARPT. WITH OXYGEN MASK ON; ATC DID NOT UNDERSTAND MY RADIO CALL AND ASKED ME TO REPEAT. ANOTHER FLT RADIOED THAT I WAS RPTING SMOKE IN THE COCKPIT. ATC INFORMED ME THE 2 NEAREST ARPTS WERE ZZZ3 AND ZZZ4 AT 20 MI AND 30 MI AWAY. I CHOSE ZZZ4 BECAUSE I WAS SURE IT HAD ARFF CAPABILITY. IN GOING THROUGH THE QRH; WE STARTED TO COME TO THE CONCLUSION THAT IT MIGHT BE AN INDICATION PROB; BUT STILL WAS NOT SURE. I CALLED BACK TO THE FLT ATTENDANT TO SEE IF SHE COULD OR SMELL ANY SMOKE. SHE SAID NO. WITH NO ODOR OR SIGN OF SMOKE IN THE COCKPIT; I CHKED THE AVIONICS EXTINGUISHER HOLE TO FEEL FOR HEAT AND OR SMOKE; I COULD NOT DETECT ANY. I WAS MORE CONVINCED WE DID NOT HAVE A FIRE BUT STILL FELT THE BEST COURSE OF ACTION WAS TO CONTINUE TO ZZZ4 WITH THE OXYGEN MASKS ON IN TERMS OF SAFETY. I REAFFIRMED WITH ZZZ4 TWR WE WERE AN EMER ACFT AND NEEDED THE TRUCKS. UPON LNDG THE ACFT WAS STOPPED AND SHUT DOWN AND WE DEPLANED THE PAX WITHOUT FURTHER INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT HIS ACR'S MAINTENANCE BELIEVED THE AVIONICS SMOKE DETECTOR FAILED AND GAVE THEM A FALSE WARNING. A GREAT DEAL OF INCIDENT REVIEW OCCURRED FOLLOWING THIS EVENT WITH THE FAA; ACR MGMT; UNION REPS; PILOT TRAINING DEPT; AND MAINTENANCE. THE ACR WAS NOT PLEASED THAT THE CAPT DIVERTED 30 NM SHORT OF ITS DESTINATION. THE FAA AND UNION APPEARED SUPPORTIVE BECAUSE THE ACFT IS DESIGNED TO IMMEDIATELY VENT SMOKE OVERBOARD NOT ALLOWING CIRCULATION IN THE ACFT INTERIOR. BECAUSE OF THIS DESIGN FEATURE AND THE FACT THAT THE CREW HAD THEIR SMOKE MASKS ON THEY MOST PROBABLY WOULD NOT HAVE SMELLED THE SMOKE. THE CRASH FIRE RESCUE CREW DID NOT SEE SMOKE AFTER LANDING BUT THE CAPT ELECTED TO HAVE THE PAX EXIT THE ACFT VIA A NORMAL STAIR IN ORDER TO ERR ON THE SAFE SIDE. SUPPLEMENTAL INFO FROM ACN 758510: ENRTE RED AVIONIC SMOKE ILLUMINATION ON CWP AND TRIPLE CHIME. CAPT CALLED FOR MEMORY ITEMS; MEMORY ITEMS COMPLETED AND CONFIRMED I MONITORED AND FLEW THE AIRPLANE PER LAST ATC ASSIGNMENT; CAPT BEGAN QRH. I COULD NOT HEAR HIS INSTRUCTIONS THROUGH MY HEADSET BUT COULD HEAR HIM FAINTLY HEAR OUTSIDE OF EQUIP. HE SAID CHK CIRCUIT BREAKERS. I COMPLETED INSTRUCTION AND CONFIRMED NONE TRIPPED. CAPT BEGAN COM OF EMER WITH ATC. CAPT COMPLETED QRH STILL POOR COM BTWN US AT THIS TIME. I CAN NOT HEAR HIM. I CAN HEAR ATC. I CONTINUE TO FLY. CAPT REQUESTS EMER LNDG AT NEAREST SUITABLE ARPT. WE ACCEPT VECTORS TO ZZZ4. CAPT REQUESTS ARFF. I CONFIRM. WE HAVE DECLARED AN EMER AND NEED ARFF ON SCENE. DURING THIS TIME FLT ATTENDANT WAS NOTIFIED OF THE DIVERSION AND WAS TOLD THIS IS FOR REAL. FLT ATTENDANT ATTEMPTED TO INTERRUPT OUR DUTIES SEVERAL TIMES. I RESPONDED DURING THE THIRD INTERRUPTION TO NOT RESPOND TO HER AS WE WERE FULLY TASK SATURATED. CAPT MADE REQUEST OF FLT ATTENDANT FOR FIRE OR SMOKE DETECTION. WE HAD MADE ATTEMPTS TO DETECT FIRE OR SMOKE AND DETERMINED NEGATIVE. THEN WE GOT OXYGEN WARNING LIGHT ON CWP. I CONTINUED WITH ATC INSTRUCTION FOR VISUAL APCH. WE COMPLETED NORMAL CHKLISTS FOR APCH; DSCNT; AND FINAL CHKS FOR LNDG. SUPPLEMENTAL INFO FROM ACN 758512: DURING CRUISE I RECEIVED A CALL FROM THE FLT DECK INDICATING THAT THE AVIONICS SMOKE INDICATOR LIGHT HAD ILLUMINATED IN THE COCKPIT. I WAS ASKED IF I SAW OR SMELLED ANY SMOKE IN THE CABIN. I CHKED THE CABIN AS WELL AS THE AREA IN THE CABIN WHERE THE AVIONICS SYS IS LOCATED BEHIND THE FLT ATTENDANT JUMPSEAT AND SAW; FELT OR SMELLED NOTHING AND COMMUNICATED THAT BACK TO THE FLT DECK. I WAS THEN INFORMED THAT WE WOULD BE DIVERTING AND MAKING AN EMER LNDG AT ZZZ4 AND TO PREPARE THE CABIN FOR LNDG AND TO STAND BY FOR FURTHER EVAC INSTRUCTIONS SHOULD THAT BE NECESSARY. THE LNDG WAS UNEVENTFUL AND CFR MET THE ACFT. WITH NO IMMEDIATE THREAT PRESENT; WE DEPLANED THE ACFT IN A NORMAL FASHION. POSTFLT -- EVAC PROCS WERE STILL FOLLOWED IN RELATION TO THE PAX.

Data retrieved from NASA's ASRS site as of January 2009 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.