Speedbird 744
Sick Squid is on the money, but maybe I can provide a personal example. In BA the 757 & 767 are run as a single fleet. The 5 year freeze applies to moving away from that fleet. I joined said fleet as a cadet entry. I did my 767 training (1 day ground school, 2 sim sessions and 4 line sectors) 4 months after completing the 757 training. Once qualified on the 767 you can then bid for some longhaul work as not all destinations require ETOPS - such as Dharan and Almaty. I had to wait a further 14 months before getting ETOPS qualified.
It's not in the company's interest to have single type qualified pilots on the fleet as they like the flexibility to substitute 767s on some routes when loads get high or when they need to consolidate two flights on to
one.
Any the wiser?