Not counting the two different props that I flew at school, plus one jet, I have flown and have certifications for four different size Boeing planes.
The 737, 747, 757 and 767. My favorite is the B-767, which is a two-aisle plane seating about 300 passengers. Because the 757 and 767 have almost identical avionics, I was able to alternate between the two planes. Most airlines, including United, restrict their pilots to flying only one size or model of aircraft. The more familiar a pilot is with that particular plane, the less likelihood of the pilot having issues. That doesn't mean that a pilot cannot switch aircraft during his career at any airline, he just has to prove himself by going through the training for the plane he wants to fly by training in simulators and then also flying a real plane on a real trip with a "check pilot" who goes along on the flight or flights, depending on how well he handles the new plane. Once he passes the tests involved, he receives a certification to fly that plane.
The 767 is my favorite because it was the first plane that I had flown with all digital avionics. It was heavy, which gave us a better ride and I just felt very comfortable flying the plane. When I first started flying the 767 simulator, I thought maybe I had bit off more than I could chew, but the more I flew it, the more comfortable it became to me. It was a big jump from the 737 to the 767. I liked the ride, avionics and the fact that I could carry more passengers, but the number one reason was that I was able to fly longer trips, like Washington to LA or San Francisco non stop. A 5 1/2 hour flight was something that I had been longing for. Those short jumps, like two hours or less are made for pilots who enjoy flying several legs in one day.
After I had flown the 757/767 for maybe two months, it was like sitting in my living room. It's not the plane that becomes troublesome, it's the environmental things like, extreme heat or extreme cold, heavy snow or rain, sleet or hail, high winds or circling winds. Things like that will cause a pilot concern and test their fortitude. If we get into some heavy weather and I would have to turn off the A/P (Auto Pilot) and hand-fly the aircraft, it becomes more challenging. During these times, it allows the pilot to use his skills as an aviator and his goal then becomes to get everyone on the ground safely. Safety is always priority one.
Thanks for asking this question. I hope that anyone who may have read my answers has a better understanding of what pilots are expected to know during those times when a pilot cannot allow the A/P to do his flying for him. We also have to spend 'x' amount of hours a year in the simulator under different conditions. You can be flying along and all of a sudden the number one engine flames out. OMG, now what do I do? Or, maybe the rear cargo door flies off while at 37,000 feet. Another, OMG, what do I do? These are just a few of the programs that are put into the simulator. You're sitting there just flying along and BAM! Something goes wrong. The check pilot inside the simulator with you is carefully watching as you make the necessary adjustments or changes to get out of a bad situation. Hopefully, you're up to the challenge because you are being graded.
"Come fly the friendly skies of United." (I love that slogan.) The new slogan is "It's time to fly." (Blah.)