The fan not coming on would be electrical or the circuit board for the furnce for a probability. Could even be to contacts etc in the thermostat or a broken wire. No Flame can be the circuit board or the gas solenoid valve if the pilot lights or if the pilot won't light, it could have a spider web built across the end or inside as spiders love the gas smell. Pilot light won't stay lit would likely be the thermocouple is bad. Then there was a few furnaces that didn't use a pilot light but used an electric ignition or piazo spark. Look for the obvious first as to what is happening and then you'll have more info. I'm not sure which furnace AF used in 2006. A lot more info is needed first.
An RV place is always a good help too and perhaps they know exactly what the problem is so it wouldn't be costly.
