The challenges are:
- Complex systems you've never seen in a GA aircraft that you need to know inside and out....turbines, pressurization, flight management systems, flight manifests, weight-specific performance limitations, etc.
- A machine that cruises 3-4 times faster than the average machine you've been flying at altitudes 4-5 times higher than you're used to flying...meaning much more involved descent planning.
- Flying SIDs and STARs at those speeds and altitudes while trying not to spill anyone's drinks.
- Going into and departing from the biggest, busiest and most complex airports in the world with four ramp control frequencies, four ground control frequencies, three tower frequencies and two or more departure frequencies all dependent on where you're parked and where you're going. Plus the company frequencies for logistics things.
- Adhering to very rigid checklist and crew coordination standards while doing all of the above.
- Understanding and complying with maintenance records, MELs, etc. before each and every flight.
It's pretty overwhelming at the outset. I'm sure it'll seem routine and easy six months from now, but the first month or so you're paddling as fast as you can and still ending up several miles behind the airplane!
But that first year FO paycheck makes it all worthwhile!