Once at the parking position, engines are shut down according to need and practice.
- Ground power is usually connected on the front right hand side, underneath the flight deck. For this the right hand engine/s are shut down for the safety of the ground staff. Once power is transferred (internal lights tend to blink on and off) then the left engine/s are shut down. Only at this point may other personnel approach the machine, indicated by the flight crew in switching off certain red rotating beacon lights.
- If no ground power is available (remote out station or the company choose not to pay the airport for the service) the crew will use the Auxiliary Power Unit (APU) which is a mini jet engine situated at the base of the tail fin (called the vertical stabiliser but my anorak is beginning to rustle so I'd better be careful!) this provides all electrical power required and the engines can be shut down.
The APU is used for a number of tasks and I shan't bore you with them here - unless you are foolish enough to ask!
Lastly, there are batteries to cover emergency lighting and basic radio functions etc.
[PAXboy crams his anorak back into the wardrobe]