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Is there any way to tell what the internal designations of an airline mean? Looking at Delta's seat maps for the 757, Delta has a couple of kinds, but what's the difference?
Boeing 75A Boeing 75M Boeing 75S Boeing 75G
I know they're slightly different configurations for different routes, over water etc, but can what type is used on what route/configuration or what the designations mean be found somewhere?
Is there a place where these are defined for airlines of the world?
These are internal references for Delta's large fleet of 757s, and they represent modifications (such as ETOPs, variations with winglets, etc.)
As you may know, Delta and Northwest merged so a lot of these aircraft are ex-NW aircraft which have been merged into the Delta fleet.
They differ mainly in the amenities (some have lie-flat seats, or overhead video); and others are certified for ETOPs (a fancy way of saying the aircraft is certified to fly over water far away from land).
The 75A is a variant of the 757-200ER (Extended Range). This aircraft is most commonly used on Asia routes as it is ETOPS enabled. These are almost exclusively ex-Northwest aircraft. These aircraft have overhead video.
The 75M is used on domestic flights; and has on-board wifi; but that's about it. Its a variant inherited from the NW merger.
The 75S is one with winglets and in-seat power, and in-seat entertainment.
The 75G is an older variant that has very little in terms of creature comforts.
One place to find these (other than seatguru) is planespotters.net which keeps an updated list of airline inventory
The 75G vs 75A nomenclature is Delta's in house numbering, not an industry standard. Each airline configures each aircraft it buys in whatever interior configuration they feel best suited for the route(s) intended for that aircraft.
Delta's multiplicity of 757 variants is not the norm, rather is due to the merging of aircraft from Delta, Delta Song and Northwest.
On the other hand you do have numbered variants, like 737-200, 737-400, 737-900, these are actually designated by the manufacturer and refer to the different versions of the aircraft's structure (body length, wing design, fuel capacity, engine acceptance, etc).
As for determining which is to be used for which route, some of the Delta seat maps mention a configuration's usage, such as "Hawaii routes" or "transcontinental". But as airlines switch aircraft around to best meet load needs, they are not guaranteed.
