The compass swing does not garrantee that the compass will give a true reading / deviation with all states of electrical load.
Again its this old cherry of read the POH it will specify what it is swung using. And usually there is 2 bulbs in a compass linked in series, one either side which cancel each other out. They are in series so it fails safe ie if one bulb goes it stops the other one working so the whole lot still gives the correct reading.
My day job type needs for you to get a resonable reading all sorts of stuff turned off. And normally sits with about 30 degrees error on it. And the most use it gets is for jamming a chart behined when the sun is in you face. And the stuff you do require to turn off means that you are flying on standby instrument power and you will have gone onto timed turns from ATC.
And the point on re-racking is to be honest bordering on dangerous. Re-racking even in the hands of an avionics engineer must be the quickest way of shagging sevicable equipment ever invented. Bent pins, wear and tear. Turn everything on and dry it out is by far the safest way to both yourself (less chance of slashing your hand open on sheet metal) and to the plane of not bending delicate connections.
The pitot heater is one of personal preferance persoanlly now I would have it on all the time. When instructing I had it on at night or IMC.
And the DME argument is very nice but. In reality most modern area nav equip planes will be using and speaking to 6 if not 10 different DME stations. And the likes of TLA or POL can accept over a thousand requests per cycle. A terminal ILS DME must be nearly 500. In the UK i wouldn't worry about it leave it on if you want. If the big boys use a DME slot when they arn't even using it for primary nav so can a SEP. If you don't get a reading inside the DOC NATS need to know so they can upgrade the installation as required. If they don't know they can't fix it.
Turn the whole lot on leave it on would be my advice and if you really don't want the DME just tune it to a freq which isn't used.
MJ
Last edited by mad_jock; 15th December 2005 at 10:42.