Problem with the spiral dive technique is that it is, in itself, an abnormal situation
It's only abnormal if you don't normally do it, it a simple technique with quite a few applications. Nothing abnormal about it if you practice it regularly. It is taught as part of the CPL course and is a really simple and usefull tool for getting down quickly in a small area.
Teddy R - I said nothing about hill fog. Just if the cloud base and terrain height are close how do you make the call? Neither did I mention single engine, having said that the only difference you have in a twin is the option to keep flying whilst on fire! Besides, anyone who regularly does ferry flying will inevitably have to fly single engine IMC over high ground sooner or later.
Opening the throttle just adds air to an engine fire. If you read any aircrafts POH it will recommned closing the throttle as the first course of action in order to starve the combustion chamber and manifolds of air. Quickly followed by mixture to ICO (obvioulsly). Opening the throttle might clear the lines of fuel, but the fuel you are clearing will be fueling the engine fire. Cutting the mixture will isolate the fuel lines. (which should be fireproof).
The only time you should open the throttle in case of fire is during start up. I think the reason for this is because most fires on start up are caused by over-priming.
That is what I have been taught, but I stand to be corrected!