ICAO use a code system, known as the Aerodrome Reference Code, to specify the standards for individual aerodrome facilities which are suitable for use by aeroplanes within a range of performances and sizes. The Code is composed of two elements: element 1 is a number related to the aeroplane reference field length; and element 2 is a letter related to the aeroplane wingspan and outer main gear wheel span. Thus 4C is an aeroplane reference field length greater than 1800m (4) and wingspan 24m to less than 36m/outer main gear span of 6m to less than 9m (C). This detail (and all the limits) is found in the ICAO aerodromes manual, and the UK CAP 168 at section 2.2, and in similar publications from other countries. The linkage between aerodrome reference code and minimum runway width is found in the same publications, such as section 3.2 of the CAP 168
http://www.caa.co.uk/docs/33/CAP168.PDF
Note that the aeroplane reference field length is solely for the selection of a Code number and should not be confused with operational runway length requirements, which are influenced by other factors. [I like to think of it as TORR for accountants <grin>]
This ICAO Aerodrome Reference Code is not the same as the JAR-OPS aeroplane category which is related to indicated airspeed at threshold (such as JAR-OPS 1 Subpart E, Appendix 2 to JAR-OPS 1.430c). Confusingly, the codes look similar. There was a Tech Log post a couple of years ago where the circling minima (which were in terms of aeroplane category) were linked to the runway strip width (in terms of aerodrome reference code) and it had me confused for quite a while until I turned up a simplistic rule of thumb that the bit where the aircraft is on the ground is dominated by the ICAO Aerodrome Reference Code, and the bit when it is in the air it is dominated by the JAR-OPS aeroplane category. The link between operations, JAR-OPS, and the aerodrome reference code is found cryptically in JAR-OPS 1.220 where
An operator shall only authorise use of aerodromes that are adequate for the type(s) of aeroplanes and operation(s) concerned
All model B737s are code 4C aircraft, from the -200 throught to the -900. The A320 is a code 4C aircraft. The A310 is a code 4D aircraft (like all widebodies and the longer narrowbodies including the B757-200).
There are lists published of aircraft with their ICAO aerodrome reference codes to save having to work it out each time. The Australian list is in Chapter 2.1.6 of their MOS139. The Transport Canada have another list. The Oz one is here:
http://www.casa.gov.au/rules/1998casr/139/139m02.pdf
It is interesting to see the interpretation of this requirement in action. If the aerodrome is not adequate for the type of aeroplane/operation under JAR-OPS 1.220 (and I think that failure to meet ICAO runway width might be such a case), then the operator/authority must do something to make it adequate. This is done here by adjusting the operation to make the aerodrome suitable. Putting operational limitations in place to cope with the effect of reduced width is a way of doing this (such as those limits discussed in earlier posts), and clearly is a common enough action.
I am familiar with B737 ops on 30m wide runways - both the -400 and the -800 series. They are normal at several Australian aerodromes, such as Ayres Rock and the busy Gold Coast/Coolangatta; even though the bulk of Australian 737 operations are on 45m wide runways. I have seen the written dispensation by CASA to the operator for at least one of these 30m runway operations, and it was an open-ended dispensation [that is, it was without time limit although I think there were some operational restrictions]. I reckon there must be some such dispensation in place covering operations at other 30m wide runways elsewhere in the world, because this ICAO runway width requirement is a very long standing one and not easy to ignore.