Thanks for your reply OverRun. I find this to be a fascinating subject and I have learned a lot from your posts.
It's pleasantly surprising to find just how much difference a new technical assessment can make to a PCN. As far as I know, the PCNs for taxiway alpha, runway 06/24 and the main apron at EDI have remained relatively unchanged since they were built in the mid 70's so I presume that the previous owners, BAA, never carried out a full re-evaluation of the PCNs, otherwise they would presumably have discovered what the new owner, Global Infrastructure Partners (“GIP”), have just discovered. It would appear that one of first things that GIP did (either as part of the due diligence / survey process while they were bidding for the airfield or in the few days immediately after the purchase was announced) was to re-assess the PCNs of some sections of the airfield and the results have included some very substantial upgrades to PCNs.
The previous PCN of the centre section of taxiway alpha (72/R/C/W/T) limited the maximum weight of a B773ER to around 595,000lbs assuming that ACN<=PCN. The re-assessed PCN enables the same aircraft to operate at its maximum take-off weight of 775,000lbs. (Note however that runway 06/24 is currently too short and has too low a PCN for that weight; Boeing’s detailed performance charts indicate that circa 720,000lbs would be the maximum take-off weight from a dry 8,600ft runway on a standard day if the PCN is suitably increased but the current PCN of 74/R/C/W/T would limit take off weight to 605,000lbs assuming that ACN<=PCN. If a 10% overload is permitted then take-off weight could be higher.).
The remaining two sections of taxiway alpha were upgraded from 72/R/C/W/T to 120/R/C/W/T (without any works being undertaken), and taxiway mike was upgraded from 31/F/C/X/T to 37/F/A/W/T (without any works being undertaken). My suspicion is that, if a new technical assessment is carried out on the rest of runway 12/30 (taxiway mike is part of 12/30) it might also be 37/F/A/W/T and this would go a long way towards explaining why the occasional large wide-bodied aircraft has been allowed to taxi and park on this runway in the past.
It'll be interesting to see whether GIP also revises the PCNs of the aprons and 06/24 at EDI in the coming months. Our previous discussion in this thread about how much additional asphalt would be needed to increase the PCNs at EDI might become irrelevant if it turns out that the subgrade on 06/24 and the aprons is re-assessed as high strength and the surface is re-assessed as flexible.
In the context of the costs of operating an international airport, and based on the re-assessment processes that you have described, it doesn’t sound like re-assessing PCNs is a particularly expensive task, yet the benefits can be very substantial.
Last edited by Porrohman; 25th July 2012 at 13:45.