A system of code numbers and letters selected for aerodrome planning purposes in accordance with the characteristics of the airplane for which an aerodrome facility is intended. The aerodrome reference code number and letter have the meaning assigned to them as indicated in the table. For example, in the table, the code number for element 1 (column 1) is determined by selecting the value of the airplane reference field length for which the runway is intended in column 2. The determination of the airplane reference field length is solely for the selection of a code number and is not intended to influence the actual runway length provided. The code letter of element 2 (column 3) is determined by selecting the greatest wingspan (column 4) or the greatest outer main gear wheel span (column 5), whichever results in the more demanding code letter.