Zurich based Swissair has always been a loyal customer to Mc Donnel Douglas in its history but the airline is going for an all-airbus fleet which will bring fleet commonality between all aircrafts.
Swissair, which is well known for its excellent service on board, was founded in 1933 and quicky introduced the Douglas DC-3. Then came the DC-4 which was introduced on transatlantic flights. At the dawn of the jet age, Swissair ordered the DC-8 which was competing against the Boeing 707. They also ordered the Convair 880/900 but those didn't fly long, I guess this was because they weren't as efficient to operate as other types in the fleet. The DC-9 was introduced on short to medium haul flights within Europe and in the beginning of the widebody era, the DC-10 was introduced on long haul international flights. It was not surprising that they were the launch customer of the MD-80 and that they helped Mc Donnel Douglas launch the MD-11 in the mid 1980's. Someone said that ten years ago, Swissair was exclusively a Mc Donnel Douglas customer, this is not true because they had already the Airbus A310. Swissair was the first airline, with Lufthansa, to put in service the A310 in the mid 1980's. It was also an early customer for the Fokker 100 but they recently removed the type from the fleet. Gone are the DC-9's and MD-80's, gone also are the DC-10's. A few A310's are still around but they will be phased out in favor of the A330. I beleive that Balair, also a Swiss airline, still flies A310's.
The last 747-300's, for which the airline was also the launch customer, are going to be removed anytime soon. Sabena just retired its last 747. The 747's (Swissair's only Boeing product) are going to be replaced with Airbus A340's like you said. The MD-11's, yes the one involved in the disaster of flight 111, are still young and they will soldier on the long range sector a few more years. Like I explained above, Swissair was an early customer for the MD-11 which was meant to be the DC-10's replacement. They will be gone in the mid-2000's as more A330's are on their way. It is now the only Mc Donnel Douglas type left in the fleet.
The MD-80's and Fokker 100's are all replaced with Airbus A319/A320/A321's and the 747's and MD-11's are going to be replaced with A330's and A340's. In the near future, Swissair's fleet will consist excusivley of Airbus types: the A319/A320/A321 on short to medium haul flights within Europe, the A330's and A340's on intercontinental flights. All these types have low noise emissions.