Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 24.4; Flight Crew Total 4020; Flight Crew Type 1966
Confusion; Other / Unknown
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Became Reoriented; Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control; General Declared Emergency
Aircraft; Human Factors
VMC at 6000 requested climb to 8000. 8000 was IMC with temp. +1. Moved forward in seat to inspect wing leading edge for possible ice; negative. Panel went 'black' Chelton panel dark; MX20 dark; GNS 480 dark; no autopilot; no transponder; no comm radio; headset noise cancelling off.  Resulting panic. No transponder or comm but had an 'emergency'; needed time to assess; needed VMC.  Began descent to 6000 exiting clouds in unusual attitude; corrected attitude; assessed situation after selecting 'nearest' airport. FOUND AVIONICS MASTER TO BE IN OFF POSITION. Turned on avionics master; significant reduction in panic but still disoriented and seeking to land safely to assess calmly what happened. With radio back 'online' called center to explain and declare emergency and accept assistance in navigating. Still uncertain what to trust with multiple yellow flags on Chelton EFIS. Visual approach where I spent the night before resuming flight VMC next morning after analyzing what had happened.Assessment: While moving seat forward and twisting to inspect wing leading edge for icing caused knuckle; kneeboard; watch or something to unknowingly depress avionics master to off position. Sudden roar in headset (thinking rapid decompression) black panel; thinking catastrophic failure leading to panic.  Getting to VMC very helpful in rationalization of circumstances. Avionics master switch is recessed for protection from incidental switching but somehow must have hit it 'just right'! Have reviewed with recurrent trainer to incorporate in training scenario so others might recognize symptoms. I'll never forget!
A C210 pilot reports inadvertently switching off the avionics master switch while leaning forward to check the wing for ice. All panels go dark including COMMS (Communications) and autopilot. A descent is initiated; ATC is advised; and the aircraft is recovered in VMC. The switch position is detected and corrected; but the reporter elects to divert and spend the night.