The no centre seat occupant restriction in falling snow on the Hughes 500 is because the original engine relight switch box was located lower on the console, and was difficult to reach with the centre seat occupied. All of our 500's (I'm talking in the 80's) had the relight moved to the upper right of the panel, and the centre seat restriction was lifted. It has nothing to do with C of G or the Filter Bypass door.
It is difficult to nail down blanket rules for flight in snow, as each helicopter and situation are unique. Not sure I can go along with the 'zero/zero' technique. This may work for very light snow conditions at airports but is not appropriate for use in heavier snow or unprepared sites, and can lead to more trouble than its worth.
One method commonly used for take-off in snow is to start to apply a little power until the snow begins to fly, retaining reference with the ground. Continue to apply power without going airborne until the snow has diminished to the point where a good reference is available. Lift the aircraft into a low hover, keeping your reference visual, then climb to a high hover and depart over the snowball. The main thing is to keep some reference available at all times.
For landing, plan your approach to a spot with some form of reference available. This can be the side of a building, a small tree, a fuel drum, etc. Bring the aircraft into a high hover, while maintaining reference with your spot, and allowing the downwash to clear the snow. Slowly lower the aircraft to the landing site as the clearing snow permits visual contact to be maintained.
Thomas Coupling...I have to take exception with several of your points. You say "Do not fly in visible moisture below +5 degrees, is good karma for MOST civvy helos. Due to the venturi effect at the engine intakes (Po) this drops to just above freezing and the engines could cut out!" This is absolute rubbish.
You also say "This time don't fly in snow below 0 degrees due to icing." Again, rubbish.
And...."If you've been on the frozen deck for too long, you may stick to it sufficiently to overtemp an engine trying to break free!!" Over temp in winter? What exactly do you fly?
Flight in snow, when properly equipped is as safe as flight in rain. There are places in the world after all where flight in heavy snow conditions are a daily occurance, and operations are conducted in a safe and efficient manner. Mr Coupling...If you don't know what you're talking about, please don't impart your dangerous level of inexperience on others.
[This message has been edited by Tiercel (edited 06 March 2001).]