With a fire warning it is unfortnuately very difficult to work out whether it is a false warning, how severe it is etc. Therefore I am of the opinion that a "solid" fire warning (as opposed to an intermittent one which, by its nature is most probably a false warning) should be dealt with immediately. If you wait until something else goes visibly wrong in the cockpt, it may well be too late.
To mad-jock I would say that perhaps things are slightly different for fixed wing for a few reasons such as the physical separation of one engine from the other, and from the wider distribution of flight-critical elements such as control runs. In a helicopter, if the firewall between the engine and the main transmission is breached by the fire, it can well take out all the hydraulics etc. So the first thing you would know, apart from the fire warning, would be complete loss of control, upside down in a second and dead in 5.
Ultimately I think it would come down to how the aircraft was certified against the requirements for dealing with fire. There is probably some presumption in the certifcation rules that the pilot will carry out the fire drill within x seconds of the fire warning (where x is not very long!) and the airworthiness of the aircraft will be based around that. So if you delay, you are into uncharted territory and flying on a wing and a prayer.
Its true that false alarm rate exceeds the real fire rate by a large factor, and that shutting down an engine near the surface is a high-risk thing to do, however this is why we have 2 pilots and lots of training! In a modern heli such as the EC225, the pilot just has to press the GA button and then there is nothing left to do except the fire drill - the heli will be climbing and accelerating whether on one or two engines. Therefore whether the drill is carried out at 500' or straight away at say 150' seems to make little difference to me in terms of ensuring a safe flight path. However hanging on blazing away until 500' could be fatal (ask the pilots of Concorde!).
That is why in Bristow we teach "nothing shut down below 500' except in case of a fire..."
Edited to mention that the EC225 has a little trick up its sleeve which is that if for example you operate the training idle switch, the engine runs down to idle at the maximum rate (ie very quickly!). However, if you move the engine control switch to idle, the engine slows to idle much more gently over several seconds. Thus if on that bad day you do move the wrong switch, you get a second or so to change your mind before significant power is lost from that engine.
Last edited by HeliComparator; 18th Dec 2012 at 13:04.