I have rooted my Galaxy S2 using root explorer and was able to add any amount of coins, money and fuels to Airport City.
This should also work for Samsung Galaxy S3. Just follow the steps.
Using Root Explorer, open "data/data/com.gameinsight.airport/shared.prefs/com.gameinsight.airport.xml"
Copy and paste the original xml file on memory card as a back up.
Then copy it in other place in memory card rather than back up and connect your mobile to a PC and copy the file and rename it as "alteredapc".
Open it using Wordpad. Search for "icoins" which should look like this
="Player/m_iCoins" value="XXXX"
XXXX is your present coin value. Change the value to your wish.
Repeat the same for "imoney" and "ifuel" values.
Place the altered file back to your memory card.
Open the file using Root Explorer, copy and paste it in the original game file.
That's it. Now you have your desired amount of coins, money and fuels to use in Airport City.
BTW, I'm playing Airport City on my Samsung Galaxy S3. So, please send me cheats/hacks for this game.