whats with the obsession with PCNs- its made jack sh*t difference to any of the comings and goings much to the stories and theories in the past.
All airports have limitations. Some airports are restricted by runway length, some by noise restrictions, some by obstacle clearance and some by other factors. Edinburgh's historic limitations (air-side) for long haul were PCNs and the small number of large stands. The latter improved with the creation of stands 2A (B788), 3 (B76W) and 4A (B76W), though they can't all be used at once. It will improve further with the creation of stand 12 which should become operational during the spring and will be used for the Qatar B788 and the Etihad A332. I'm not sure whether stand 12 will be large enough for a B773ER; these aircraft currently need to use stand 17 on the SE apron which then restricts payload / range due to the weaknesses of taxiways Lima and Mike. PCN's at EDI are adequate for current wide-bodies operating current and announced routes but would need to be increased if EDI has aspirations to attract operators of higher ACN wide-bodied aircraft in years to come. PCN's may have been a factor in influencing Emirates' decision to operate from GLA rather than EDI.
To illustrate the importance of PCNs and ACNs, the approximate weight limits for relevant parts of the EDI infrastructure for a B773ER are as follows. The restrictions that apply to any particular flight depend upon which apron and taxiways the aircraft uses;
- Empty weight ~380,000lbs
- PCN of Taxiway Lima; ~390,000lbs at ACN=PCN (See page 153 of Boeing data - this chart doesn't go as low as ACN=31 for a C strength subgrade so I extrapolated)
- PCN of Taxiway Mike; ~530,000lbs at ACN=PCN (See page 153 of Boeing data)
- PCN of Main Apron and SE Apron (72/R/C/W/T); ~595,000lbs at ACN=PCN (See page 156 of Boeing data)
- PCN of Taxiway Alpha A8-A16 (70/F/A/W/T) ~667,000lbs at ACN=PCN (See page 153 of Boeing data)
- PCN of Runway 06/24 (87/R/C/W/T); ~675,000lbs at ACN=PCN (See page 156 of Boeing data)
- Length of Runway 06/24; ~712,000lbs on a Standard Day (See page 48 of Boeing data)
- PCN of Taxiway Alpha A1-A8 AND A16-D1 (120/R/C/W/T) no restriction (See page 156 of Boeing data)
NB. Maximum take-off wight of a B773ER is 775,000lbs where airport infrustracture is compatible.
Sources;
http://www.boeing.com/assets/pdf/com...777_2lr3er.pdf and
NATS | AIS - Home
Exact weights depend on a great many more factors than are addressed in the referenced charts so these figures are just indicative. Actual figures for a given aircraft on a given day operated by a given airline could vary significantly for a huge variety of reasons.
I've used the B773ER as an extreme example of the PCN limitations. Other aircraft types are better suited to EDI's various current limitations.
Many years ago, I wondered whether the runway length at EDI was an impediment to long-haul flights but it transpired that PCNs and stand sizes were more of a constraint. A B773ER operating from the only stand at EDI that is currently large enough to accommodate it (stand 17 on SE apron) is currently payload/range limited by the weakness of taxiway Mike (~530,000lbs for ACN=PCN). During BAA ownership, taxiways Lima and Mike had the same PCN (31/F/C/X/T) so the payload/range back then was limited by the weakness of Taxiway Lima (~390,000lbs for ACN=PCN). Interestingly, the upgrade to the PCN of taxiway Mike occurred about one week after GIP took control and was prior to any strengthening works taking place. Taxiway Mike must already have been that strength, but the data provided by BAA to NATS, for whatever reason, had been more conservative than GIP's assessment of its strength. If the new stand 12 on the main apron is large enough for a B773ER the payload/range is limited by the PCN of the main apron (~595,000lbs at ACN=PCN). If the main apron is strengthened, the payload/range is limited by the PCN of the centre section of taxiway Alpha (~667,000lbs at ACN=PCN). If that is strengthened, the payload/range is limited by the PCN of runway 06/24 (~675,000lbs at ACN=PCN). If the runway is strengthened, the constrain becomes the length of runway 06/24 (~712,000lbs on a Standard Day). Assuming that ACN=PCN then PCNs are more of an issue for a B773ER at EDI than runway length on a Standard Day.
As previously mentioned, there's a possibility that a 10% ACN>PCN overload might be allowed but, assuming that the data that EDI provided to NATS is correct, taxiways Lima and Mike are weak-points of the current infrastructure at EDI. NB. On an occasional basis, ACN>PCN overloads greater than 10% can and have been permitted, but CAP168 requires inspection of the pavement by a competent engineer after each such operation. This explains the occasional operation of larger aircraft from the SE apron and also explains why such operations are not regularly undertaken from the SE Apron.
GIP are gradually improving the situation and I expect that, if there is the demand, they will make further improvements provided that the payback justifies the investment.