Dear TC. On the understanding that the single engine helicopter pilot should always have their hand on the collective lever, there are going to be times when they do not for various good reasons. Should the pilot suffer an engine failure during one of these situations, then if their first action was to lower the lever they would most probably end up being a passenger until they hit the ground. It will take a period of time for the pilot to recognise and react and a further period of time to move their hand back onto the collective lever and lower it. However they will always have their hand on the cyclic, therefore able to trade airspeed for RRPM in a much shorter time scale, it has to make sense to use airspeed energy should you have it. The understanding is that this energy transfer is transient, the pilot is going to have to put that lever down, it just allows for a bit more time to do so. I would go so far as to say; ' it should be a criminal offence for a helicopter pilot not to try and use all available energy to prevent Low RPM rotor stall' DS.