a/c cargo compartments - questions
 

With respect to commonly used medium and long-haul passenger aircraft (any type you are comfortable talking about):

Can someone outline how heating and cooling of lower deck cargo compartments is accomplished? Is there a direct air exchange (air vents removing air from and/or supplying air to the compartment) or is heated/cooled cabin air just passed along the outside of the cargo compartment walls to facilitate a temperature change?

How do cargo compartment temperatures compare to cabin temperatures?

Is there a technical difference with regards to heating/cooling between class C and class D compartments?

How does one verify by looking into a cargo compartment whether this is a class C or a class D compartment?

For the last part of your question you might start here.
Cargo Compartment Classification

Regards,
TT

Heating of cargo compartments will depend on the aircraft. 737 classics, the rear hold wasn't heated wihile the forward hold was heated via exhaust air from the equipment cooling vent, this is a fairly common philosophy in the Boeing fleet, the larger aircraft also have temp controlled aft cargos and bulk cargo. This can be controlled from the flight deck for temp sensitive cargos. hope this helps. Don't know how Airbi are heated....:ok:

Class D
 

I read through the classification of cargo compartments.

It appears that both a class C and a class E compartment can be ventilated.
There is no mention of a class D compartment? Yet, I have seen it mentioned frequently.

Is a class D compartment the one where a fire would be starved of oxygen because the compartment is airtight in flight?

I thought all class D compartments had to be reclassified as C or E, perhaps that is why.