Rockford RFD
TRIPLE-TANDEM TRT550 RY 07/25 & TRT590 RY 01/19.
Following my posts above on this topic, rather than interpolation, we can apply the two basic steps required for the "Using aircraft PCN" to find out what the Boeing 777 limits are:
1. Determine the airplane with the highest ACN in the traffic mix currently using the runway. This is the critical airplane.
Using TRT550 as being the critical plane, and guessing this is a C-17 at 550,000 lbs. Then from the C-17 ACN chart (newly minted at
http://www.geocities.com/profemery/a...html#ACNcharts)
a C-17A at 550,000 lbs (which divided by 2.2 = 250,000 kgs) has an ACN for an assumed subgrade of rating B of 55.
2. Assign the ACN of the critical airplane as the PCN.
Assign the ACN 55 as being the runway PCN = 55
3. From the Boeing 777 ACN chart (same source as the C-17 chart), for the same assumption of subgrade of rating B, the ACN of 55 is an aircraft weight of 226,000 kgs.
So in summary, if the RFD runway strength rating of TRT550 was actually meant as the Boeing 777, then the load limit is 550,000 lbs (or 250,000 kgs). If it was meant as the C-17, then the Boeing 777 limit is 226,000 kgs (which is 497,200 lbs). Conservatism suggests the lower limit until the airport has confirmed otherwise.
If the airport only published DT and DDT, I would still use the "Using aircraft PCN" method rather than just interpolating between DT and DDT, because that gives a rational and acceptable basis for judgement. I would then check with the airport concerned.
SpeedBird B777, your two other points:
Rome (LIRF) ISWL45000. Look I started the calculation, but the risk of confusing ISWL and ESWL is too great, and from the computer printout in front of me, the same aircraft with a SWL of 45,521 can also be rated as an SWL of 273,125 for the same load. Multiplying SWL by the number of main wheels will either be OK or a ton of grief. Sorry, but you'll have to ask the airport what they mean.
Airfields with low tyre pressure such as Y (Low, Max 145psi) listed, even though the PCN number seems quite acceptable, are doing this because the surfacing is weak although the pavement below is strong. In an emergency, you can land there. Otherwise get a pavement concession from the airport. Damage to the surfacing is possible when the aircraft is turning. The sort of damage is loose stones, which the two large Trent (Dyson look-alikes) love to suck up. This is one Greek dinner that you could directly wear the consequence of, as the fan disintegrates at takeoff power. The concession, if granted, will usually by on the basis of previous experience and/or an inspection after each landing and takeoff.