Groundloop said;
Page 150 has the ACN values and Page 156 has the chart for calculating the take-off mass for a given limiting PCN value.
Thanks for your reply Groundloop. Having read the document you pointed to, clearly it's a lot more scientific than my simple calculations. If I understand the document correctly, the ratio between weight and ACN is not a constant, as I had assumed, because of the percentage of the weight that is carried on the main undercarriage is less when the aircraft is empty and more as the weight increases.
Assuming that Taxiway Lima and/or Mike at EDI are not a limiting factor, the maximum ramp weight of a 773ER at EDI, based on the apron strength of 72R/C/W/T would be about 595,000lbs which would give a maximum take-off weight at EDI of slightly less than that, allowing for fuel burn during start-up and taxiing.
Looking at the Boeing payload /range and runway charts at
http://www.boeing.com/commercial/air...s/777rsec3.pdf for a 773ER with GE90-115BL engines on a standard day with zero winds (see page 38) would give a range of just under 1,500nm at MZFW. What would the range be with a typical economic commercial payload? I'm guessing about 3,000nm, maybe less?
The charts on page 48 show that, on a standard day, a 6,000ft runway would be required at that weight (EDI is 100ft/110ft AMSL) so, as you said, PCN not runway length is the limiting factor.
If it transpires that the PCNs on Taxiway Lima and Mike at EDI are the same as runway 12/30 (31F/C/X/T) then that would be a more significant limiting factor. If anyone knows the PCNs for these taxiways please let me know.
Comparing these figures with GLA where the PCN is 65R/B/W/T, the maximum ramp weight there would be 660,000lbs requiring a take off run of about 7,300ft and giving a range at MZFW of about 3,050nm.
I did the same calculations for NCL where the PCN is 73F/C/W/T and airfield elevation is 266ft. The maximum ramp weight there would be 685,000lbs requiring a take-off run of about 8,000ft, but as the runway is only 7,641ft long the maximum take-off weight would be limited by the runway length rather than the PCN. Looking at the performance charts, it looks like the maximum take-off weight at NCL would be about 675,000lbs.
Although PCN rather than runway length is the limiting factor at GLA, and runway length is the limiting factor at NCL, it’s easy to see why Emirates chose GLA and NCL over EDI. The ability to lift an extra 65,000lbs and 80,000lbs of fuel/payload from GLA and NCL respectively is a significant difference.
Some final questions if I may. If the PCN and ACN indicate a particular maximum weight, under what circumstances can that be exceeded, by how much, how often and on whose authority? I have the impression that PCNs are regularly exceeded at EDI so it then becomes impossible to establish what limitations apply to payload/range for an aircraft from EDI.