Scatsta was re-awarded the IAC contract just 2 years ago, with plans of extending terminal, hangar etc etc, though I believe Shell had a "get out clause" if they required. The saab 340 is out of the question as they only have circa 33 seats, so you'd only get 1 full S-92 load on it, so other than the 146, the only possible a/c would be Q400, ATR 72, saab 2K. The ATP would never be brought back into the equation after it's everlasting tech and payload problems with Britworld. I know that either Shell or Flightline had been evaluating the A318 a while back, and part of Shell's recent saftey campaigns in aviation was to bring in new technology and airframes hence the S-92's and 225's over the last 2 years. As for theory's about heli's going direct from Aberdeen, possible, but highly unlikely at present as the operators are so short of airframes and crews and doing so would make it even worse.