theredbarron said;
Nigel O, EDI's runway is only a little shorter than Glasgow's (by around 600 feet) and according to someone who should know (an Emirates 777 first officer) is quite capable of getting one of their 773ERs off at max gross.
For this statement to be true either EDI are prepared to allow an extremely large ACN>PCN overload, which I doubt would be permitted under CAA CAP168, or Boeing's published performance figures for the 773ER are wrong. I’m quite certain that Boeing’s figures are correct and it is extremely unlikely that such a high ACN>PCN overload would be permitted under CAP168; therefore I believe that the Emirates first officer is either mistaken or misinformed.
The main and SE aprons at EDI have a PCN of 72/R/C/W/T. Taxiway Alpha and runway 06/24 are slightly stronger, but that's academic as the aircraft would be loaded on the apron so that constrains the maximum weight. Taxiways Lima and Mike have a PCN of 31/F/C/X/T so until at least one of these strengthened (or a suitable stand is created on the main apron) the ACN>PCN overload of a 773ER at max gross weight at EDI would be enormous.
The 773ER at max gross weight has an ACN of 109 on the main and SE aprons at EDI vs. a PCN of 72. On taxiways Lima and Mike it has an ACN of 89 vs. a PCN of 31. Under CAP168 EDI might permit a 10% ACN>PCN overload but that is by no means certain. In any case, a 773ER at max gross weight would exceed the PCN of taxiways Lima and Mike by 132%. Even if these links are strengthened (or if a suitable stand is created on the main apron) a 773ER at max gross weight would exceed the PCN of the aprons at EDI by over 51%. At max gross weight on a standard day at sea level a 773ER needs a 10,000ft runway. EDI’s is 8,386ft.
In summary there is no way (given the current pavement strengths and runway length) that a 773ER could operate from EDI at max gross weight. Even if Taxiway Lima is brought up to the equivalent strength of the SE apron at some stage in the future, there is considerable doubt about whether a 773ER could reach Dubai with an economic payload given the other PCN limitations at EDI.
Data sources;
Boeing: Commercial Airplanes - Commercial Aviation Services - Flight Operations Support - Airport Technology - 777 Airplane Characteristics for Airport Planning (
3.0 Airplane Performance and
7.0 Pavement Data)
NATS | AIS - Home
For an explanation of ACNs and PCNs see;
Aircraft Classification Number - Wikipedia, the free encyclopedia
Pavement Classification Number - Wikipedia, the free encyclopedia
theredbarron said;
And, as I said in an earlier post, the relatively small stretch of taxiway strengthening needed is not a particularly big civil engineering job as the underlying terrain is pretty solid and stable (unlike Glasgow's marshland).
I have heard that Taxiway Lima will be getting worked on over the winter. Whether or not this will resolve the PCN limitations remains to be seen. As regards Glasgow's PCNs; they are much stronger than EDI's so your comment about underlying terrain is not relevant. EDI's runways and taxiways are built on a low strength sub-grade whilst GLA's are built on a medium strength sub-grade. The sub-grade strength makes a significant difference. GLA's main runway has a PCN of 65/R/B/W/T which to the untrained eye might look lower than EDI’s but the stronger sub-grade at GLA (denoted by the letter B) makes a significant difference. The ACN of a 773ER on GLA’s pavements is 85 so at max gross weight it would have an ACN>PCN overload of 31% (compared with an overload of 132% or 51% at EDI depending on whether or not taxiway Lima is strengthened). The net result is that a 773ER can depart GLA with a much higher payload/range than would be possible at EDI. This may explain why Emirates chose to operate from GLA rather than EDI. (NB. The NATS data for GLA does not give PCNs for the aprons.)
theredbarron said;
I doubt if anyone is planning on operating anything bigger than a 777 in the forseable future and so the problems are nowhere as large as you appear to think they are.
Size / weight and ACN are not necessarily directly related e.g. a B744 has a much lower ACN than a 773ER because it spreads its weight across four main undercarriage legs rather than two. The 773ER is the currently the worst commercial passenger aircraft for pavement loading at EDI. There are other aircraft that are better suited to the PCNs at EDI such as the A332, provided that Taxiway Lima is strengthened (or a suitable stand is created on the main apron).