I was wondering why at airports they use the air start units instead of starting the engines with their own power? Have a look at the following links, and it also mentions they are used for filling the onboard air packs.
Do they use the unit for conserving the planes own onboard power?
Aircraft use the Air start charts when the on board APU is inoperative. Most jet aircraft require air pressure and electrics to start the engines. This is normally provided by the Auxiliary Power Unit (APU). It can also provide air for the air conditioning packs for cabin temperature regulation. This use is discouraged since air charts are very loud and most airlines only have one or two at each airport. Some airlines use them with external AC power to avoid running the APU at the gate thus saving fuel.🙂
OK thanks for the info CRJCapt. 👍