As far as I know, the 340 and 330 don't have a common type rating, so no flying both.
Jim
The 757 and 767 do not have a common type rating either. On my license they are specified separately. However, the FAA permits both rating to go on the license at the same time due to the commonality of the two cockpits. In order to do this, the ground school and testing must be done on BOTH airplanes, and the Initial Operating Experience must include a minimum number of landings in each in order to be let loose on the unsuspecting customers.
This sounds very much like the A330 and A340 situation. It appeared from the A330 ground school that the systems are laid out with a four-engine jet in mind. Each engine has TWO hydraulic pumps, for instance. My hunch is that the A340 systems are much more like the A330 systems than the B757/B767.
Here is what Airbus has to say on their website:
"The A330 and A340 feature nearly identical cockpits and have highly similar flying qualities, allowing both aircraft to be operated by a common pool of pilots. In fact, flight crews can transition from the A340 to the A330 in only one day, while a move from the A330 to A340 is performed in just three days. The savings in time – which compares to 25 days for a full type rating training course required with competing aircraft – mean lower training costs for airlines and increased crew productivity.
Another advantage of Airbus commonality is a pilot's ability to be current on more than one Airbus fly-by-wire aircraft type at a time. This is known as Mixed Fleet Flying and enables a pilot rated on an A340 to switch from very long-haul operations to short- or medium-haul flights at the controls of the A320 Family. This opens new crew scheduling possibilities and provides a mix of flying opportunities that is highly appreciated by pilots."
http://www.airbus.com/en/aircraftfamilies/...ommonality.html
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Oh, and as far as flying characteristics and procedures, the A330 handles almost identically to the A320 series and the procedures are all but interchangeable.