QUOTE(rosfrog @ Jul 21 2008, 06:25 PM)

Whilst there's no danger in putting a fiddle in the hold from pressure and suchlike (people who tell you otherwise know nothing about planes)
Aircraft holds are not directly heated, unless they are carrying live cargo (a dog for example). The only air that circulates in the hold is the residue pumped down from the cabin, but bearing in mind that on a long flight the outside air temperature will be downwards of -40 celsius, the temperature within most of the hold is unlikely to be much above freezing.
Put it this way, when my luggage arrives off the ramp after a long flight, it's always very cold and that's even when arriving in temperate climates in mild weather.
However, loss and damage are the two real problems with putting musical instruments in the hold.
If you fly with BA, they will let you carry any musical instrument (violin, viola, oboe etc.) that will fit in an overhead locker, as an extra piece of hand luggage. It will need to go through the x-ray scanners at security, so make sure anything sharp that you might normally carry in the case (chinrest keys for example) or cleaning fluids/pastes of any sort have been removed and put in your main luggage, otherwise such objects will be confiscated.
For larger instruments such as a cello, some airlines will let you buy an extra seat for the instrument.
It's best to always check the airlines own policy on the carriage of musical instruments
before buying your tickets!