Narrative:

Everything was proceeding smoothly on the GPS 12 approach at dfi. I was turning inbound from the hold and I decided to tidy up the cabin for landing by unplugging my oxygen mask and stowing it in its bag. (I always have my mask plugged in and ready when flying above FL180). I pulled my left arm back to reach the bayonet plug in the armrest and all of a sudden ---- click ----the panel went blank and the radios died. I knew instantly what had happened. My shirt sleeve had caught on the avionics switch and turned it off! I flicked it back on immediately just in time to hear toledo approach say; 'radar contact lost; cancel on the ground.' what should I do? Declare a miss; or quickly reprogram the approach and try to salvage it. The most conservative decision would have been the former; but I knew exactly where I was and; at about 13 NM from the airport; I had plenty of time to sort everything out. But quickly; the sweating began. It seemed to take forever for the garmin 530 to wake up; go through its diagnostics and lock onto a signal. Meanwhile; I was on the teardrop intercept to the final approach course and had to estimate when to turn final towards the airport. But what really took me a few minutes to realize was that my HSI was still recovering from the power loss. It was reading erroneously and only when the GPS woke up and my HSI heading didn't agree with the GPS did I realize the problem. I immediately switched to my vertical card compass for heading information. Some minor s-turning got me established on final well before the FAF and the rest of the approach was uneventful. I was unprepared for the slowness of the HSI to recover. I think all the turning might have kept it from slaving quickly. Only after I was well established on final; did it start to read correctly.what did I learn; or rather re-learn? #1: sterile cockpit means more than just not talking. When shooting an approach; don't do anything but shoot the approach; even if you are just monitoring the autopilot. #2: on a low approach in actual IMC is probably not the best time to familiarize yourself with the start up characteristics of your equipment. I was surprised that my HSI didn't immediately pop back to life; but I shouldn't have been. #3: when faced with a safety-of-flight choice; always make the most conservative decision. While everything worked out well; I was disappointed in my choice after I had a chance to reflect on it. The safest thing to have done would have been to declare a missed approach; sort everything out and shoot it again. We should all be spring loaded to react like this. I knew that; but in the heat of battle; I did not do it. I vow to do so next time.

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Original NASA ASRS Text

Title: C421 pilot reports inadvertently turning off the avionics master switch during a GPS approach in IMC. The switch is quickly placed back on and the approach is continued; although some time is required for all components of the system to reboot.

Narrative: Everything was proceeding smoothly on the GPS 12 approach at DFI. I was turning inbound from the hold and I decided to tidy up the cabin for landing by unplugging my oxygen mask and stowing it in its bag. (I always have my mask plugged in and ready when flying above FL180). I pulled my left arm back to reach the bayonet plug in the armrest and all of a sudden ---- click ----the panel went blank and the radios died. I knew instantly what had happened. My shirt sleeve had caught on the avionics switch and turned it off! I flicked it back on immediately just in time to hear Toledo Approach say; 'radar contact lost; cancel on the ground.' What should I do? Declare a miss; or quickly reprogram the approach and try to salvage it. The most conservative decision would have been the former; but I knew exactly where I was and; at about 13 NM from the airport; I had plenty of time to sort everything out. But quickly; the sweating began. It seemed to take forever for the Garmin 530 to wake up; go through its diagnostics and lock onto a signal. Meanwhile; I was on the teardrop intercept to the final approach course and had to estimate when to turn final towards the airport. But what really took me a few minutes to realize was that my HSI was still recovering from the power loss. It was reading erroneously and only when the GPS woke up and my HSI heading didn't agree with the GPS did I realize the problem. I immediately switched to my vertical card compass for heading information. Some minor S-turning got me established on final well before the FAF and the rest of the approach was uneventful. I was unprepared for the slowness of the HSI to recover. I think all the turning might have kept it from slaving quickly. Only after I was well established on final; did it start to read correctly.What did I learn; or rather re-learn? #1: Sterile cockpit means more than just not talking. When shooting an approach; don't do anything but shoot the approach; even if you are just monitoring the autopilot. #2: On a low approach in actual IMC is probably not the best time to familiarize yourself with the start up characteristics of your equipment. I was surprised that my HSI didn't immediately pop back to life; but I shouldn't have been. #3: When faced with a safety-of-flight choice; always make the most conservative decision. While everything worked out well; I was disappointed in my choice after I had a chance to reflect on it. The safest thing to have done would have been to declare a missed approach; sort everything out and shoot it again. We should all be spring loaded to react like this. I knew that; but in the heat of battle; I did not do it. I vow to do so next time.

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.