Originally Posted by
172driver
BPF, I'm as much a stickler for the POH as the next guy, in fact the one of the a/c I mostly fly sits right next to me now.
However, nowhere in a POH have I yet found the phrase:
Brain - switch off
.
IMO following the POH doesn't equal "brain...switch off".
To me using your brain in the case of an inflight emergency is knowing the actions to take that will the most quickly and effectively stop/reduce your problem.
Then assessing the problem and taking appropriate steps to deal with the situation.
So in the context of an electrical fire instead of as you suggest making a radio transmission with all the electrical services still energized and potentially about to make the situation worse, I think the best way would be to follow the POH electrical fire emergency checklist starting with
immediately turning off the master to hopefully stop the ignition source.
If after completing the memory items of emergency checklist a decision is made that a radio call should be made then you should follow the POH emergency checklist to restore essential power. This will involve turning off all switches, pulling all CB's except the ones you need for one radio, looking for obvious indicators of where the problem is, like hot /melted switches/components, then turning on the master switch and making your call. These actions will minimize the chance of the smoke/fire reoccurring.
From a practical perspective the likely result of quickly removing power will be to stop the effected circuit from moving from the smoking stage to the on fire stage. Existing smoke/burning odor will likely start dissipating and so you can save re-energizing the electrical system until you get to the edge of the airspace of the nearest suitable airport and then turn on the master and make a Mayday call indicating your intentions and the fact that you are turning off all electrics at the conclusion of the radio call.
That would be the best case scenario. The worst case would be flames suddenly spurting out of the instrument panel. Again leaving power on is only going to make things worse and to me the idea that the first thing you should do in this situation is talk on the radio, just doesn't fit into BPF's brain.
IMO knowing and following the POH procedures combined with a deliberate assessment of the problem followed by actions appropriate to the situation is the best way to handle this emergency.
Finally re your note about the stall warning horn on the Retractable gear, constant speed prop equiped C172RG. Your are correct unlike the simple fixed gear fixed pitch prop C 172's which are ubiquitous at flying schools and clubs, this model does indeed have an electrically operated vane type stall warning horn. The Cessna Citation jets also all have electrically operated stall warning systems and my guess is that the average reader of this forum is about as likely to fly one of those as a C172RG.
However I will take your point that I was incorrect when I implied all C172's do not require electrical power for the stall warning system. I was thinking of the simple fixed gear series which have a reed type stall horn which activated by airflow though a fixed orifice in the wing leading edge. Systems can vary even among similar models which I think reinforces my point about reading the POH to understand how the aircraft you fly, works.