Thanks for that useful background reading material from the FAA - TheOddOne.
ReadMyACARS, the critical stage of runway loading is takeoff not landing. Runway loading is (very approximately) equal to the tyre load squared - so the heaviest tyre load (which is usually at takeoff) means more equivalent load (there are many variants to this such as the 4th power law, 7th power exponent, etc), but in practical terms it means that the weight of the landing aircraft can often be ignored in the design calculation.
Turning aircraft impose other stresses on the surfacing. And if the surface is asphalt, the visco-elastic nature of bitumen means that slow rolling or stopped aircraft raise other loading issues. But thesde are outside the ACN/PCN issue.
The loading at the moment of landing is ignored. From an earlier PPRUNE post (and reproduced there with appropriate acknowledgment)
http://www.geocities.com/profemery/a...sign_data.html
Maximum force allowed on tarmac on landing
= desirably zero because just at touchdown, almost all the lift should still be taken by the wings. If hits the tarmac with any force that implies the wings have fallen off, which is a Bad Thing. Longitudinal and lateral forces due to tyre spinup exist, but are not calculated. Instead the type of surfacing (asphalt, concrete, chip seal) is chosen according to the size and frequency of aircraft.
As for the ACN/PCN method - well the best description of its problems is given in Boeing document D6-82203: -
"there is a great amount of uncertainty … as to exactly arrive at a PCN". The method isn't intuitive or friendly to use.
Now on top of the PCN method uncertainty, designing for the B777 six wheel bogie has got most people totally perplexed. The problem with the Boeing 777 gear is that it is way beyond the old method for calculating ACN/PCN (and the antique systems for evaluating pavement loading). That method is derived from equivalency upon equivalency upon equivalency. It was a great concept back years ago for the single wheel DC-3, which was then adapted to the DC-4, and adapted to the DC-10 and adapted to the DC10-30 (with the centre gears) and …… but it can't handle the 6 wheel gear.
The current FAA design charts are generally good and I use them often, but the best system for dealing with aircraft such as the B777 and new undercarriage systems is to use a more fundamental approach such as the South African mechanistic method (SAMDM) bolstered with appropriate transfer functions. This is outside the American framework and they are having to work hard to catch up.
As for the La Tribune story about the B777 compared to the B747 - well Airbus won’t say this and Boeing is too close to the issue, but the concern is all eurocr*p. Put simply, if the runway takes a 747 then it takes a 777. crazypilot - calculate the wheel load for a few Airbus aircraft and you will find it is in the 27-28 tonne bracket as well.
I'd be pleased to trade stresses and strains if anyone differs on this - say a target pavement of 125mm asphalt on 300mm cement stabilised base on 300mm subbase on an A subgrade.