Most systems use a pump attached to the engine, which will
provide suction/pressure as long as the engine is turning.
Those pumps fail, their life is short and can be shorter if
abused during engine maintenance.
There are stand-by electric pumps and even engine manifold
sources are used in some installations. Many airplanes are
all electric [the new G1000's come to mind] and they have
redundant battery busses, generators and some also include
air driven gyros.


"Terence Wilson" wrote in message
...
| Hello,
|
| I was wondering how the primary vacuum is powered in a
single engined
| aircraft. If it was powered directly by the engine, a
engine failure
| would result in the immediate loss of attitude indicator
and heading
| indicator. So I guess most aircraft use an electrical pump
that can be
| driven by the alternator or battery, is this the case?
|
| Thanks in advance,
|
| Terence