Public transportation is the most economical way into and out of the Jinnah International
Airport Karachi, as for other part of world, but depending on the mode (bus vs train)
and the time of day it can either be the slowest way to get to the airport or the
fastest. Public buses are cheap, but make frequent stops and may require connections.
Be prepared for a longer trip in times of rush hours if taking a bus.
There are so many bus routes are available that passes though the Main Shahra-e-Faisal
almost from all the length & breath of the Karachi City. The link / access road
of Jinnah Terminal Karachi connect the Main Shara-e-Faisal to the airport.
Also note that during off-peak hours and holidays, certain options may either not
be available or may be running a reduced frequency. Make sure you have prepared
accordingly beforehand to save yourself any undue frustration.