how do I install additional Aircraft for flightgear in Ubuntu 8.04

What directory does the manual specify?

FG_ROOT/data/Aircraft

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

That probably means Flightgear's install directory, so since you installed it through Synaptic, it probably is in:-
/usr/lib/flightgear

WHOA, I am seriously sorry for all those duplicate answers, Launchpad was lagging and I was furiously pressing on the "Add Answer" button, my goodness what I mess I created, I am really sorry about that.

Sorry for the delay in replying, but I was away yesterday and have had a lot of work today.
The binary 'fgfs' is in:
/usr/games
as suggested in the manual, but I can't find a directory
/usr/.../.../FlightGear/data
which the manual suggests should be there.
With regard to installing the manual actually says:
Simply download the file and unpack it into the FG_ROOT/data/Aircraft subdirectory of your installation. The aircraft are downloaded as .tar.gz files. Some computers will download them as .tar.gz.zip files. If so, simply rename the file to .tar.gz and unpack. If you are successful, there will be a new sub-directory in your FG_ROOT/data/Aircraft directory containing the aircraft. Next time you run FlightGear, the new aircraft will be available.
It doesn't happen!!!

Did you take a look in the path I provided, i.e:-
/usr/lib/flightgear
?

yes, it was the first thing I did, it doesn't exist.
/usr/lib/flasplugin-nonfree is there and the next is /usr/lib/f-spot
I also checked for /usr/lib/fgfs
I should have said this before: Thanks for your help Pramod

Hmm, then perhaps it may be in:-
/etc/lib/fgfs

Otherwise, try doing this:-
locate fgfs
and take a look at the paths it turns up.

Hi Pramod and thanks, 'locate' did the trick. It's in: /usr/share/games/FlightGear
I am relatively new to Linux and I can't find a handy reference for the commands. If you know of one please let me know.