I feel uncomfortable with the overload limits suggested by boby4 from the Boeing/ICAO documentation. The ICAO reference used by boby4 dates back to 1983, and in my opinion the overload guidance was written more in the context of DC-3/DC-4 design runways being overloaded by narrow body jets. It is way out of line for aircraft weighing several hundred tonnes, where a cavalier 100% overload can be hundreds of tonnes extra.
I also add my sense that the aviation authorities of some States are concerned about the loss of engineering skills in their own ranks and in the ranks of the local airport staff, and getting nervous about even small very small overloads.
The 1998 Boeing document D6-82203 PRECISE METHODS FOR ESTIMATING PAVEMENT CLASSIFICATION NUMBER gives a much better approach in my opinion, with less overload permitted, and it is in line with the thinking of many airports and pavement engineers today:
For flexible pavements, occasional traffic cycles by aircraft with an ACN not exceeding 10 percent above the reported PCN should not adversely affect the pavement.
• For rigid or composite pavements, occasional traffic cycles by aircraft with an ACN not exceeding 5 percent above the reported PCN should not adversely affect the pavement.
• The annual number of overload traffic cycles should not exceed approximately 5 percent of the total annual aircraft traffic cycles.
• Overloads should not normally be permitted on pavements exhibiting signs of distress or failure, during any periods of thaw following frost penetration, or when the strength of the pavement or its subgrade could be weakened by water.
• Where overload operations are conducted, the airport authority should review the relevant pavement condition on a regular basis and should also review the criteria for overload operations periodically, since excessive repetition of overloads can cause severe shortening of pavement life or require major rehabilitation of the pavement.
And then
Any overload should be treated in terms of ACN and equivalent critical aircraft operations per individual operation. Allowance for the overload should be negotiated with the airport authority, since pre-approval cannot be assumed.
Now this should not be taken to exclude greater overloads. In my own work, at one airport we overload to 24% for three flights per week, and overload to 16% for another 20 flights a week. I’ve calculated the loss of pavement life due to overloading to be equivalent to two years for that runway, and the airport has made its commercial judgement and allowed the operations. We have an increased regime of pavement technical and engineering inspections, an airport engineer permanently on standby, and we monitor the overloads and their effect carefully by visual, FWD, rut depth and roughness monitoring. We also have an emergency overload list for very large aircraft likely to use the airport as a diversion, and their permitted landing weight for an emergency 50% overload. There are some airports with similar regimes.
But there are many more airports without the technical support, and that is where the 5% / 10% limits come into play. With the airport’s prior approval of course.
There is an easy way of checking the ACN at various weights. ACN charts for many aircraft, including some obscure ones, are
here