STACKFLOW is a trial procedure (agreed between Scottish, Edinburgh and Glasgow) which specifies a revised method of integrating LANAK arrivals and TWEED arrivals into the approach sequence. The primary objective of the trial is to allow ATC to manage the increasing number of arrivals into Glasgow and Edinburgh at peak times, but it should also afford better situational awareness on the flightdeck, because any necessary delaying action will be absorbed in a standard holding pattern (in a low drag configuation), rather than with excessive radar vectors and very early speed reductions (with consequent high drag). It also allows GLA and EDI Radar much more flexibility in determining an appropriate final approach sequence.
During peak hours Scottish TMA controllers will still continue to stream arrivals (subject to their own workload), but they will be transferred to Approach on their own navigation to LANAK/TARTN/TWEED. The revised procedures should be largely invisible to crews, but they can expect descent instructions to achieve their allocated stack levels 5 or 10 nautical miles before the holding fix, so that they can be transferred vertically separated from other arrivals.
It is not expected that there will be any significant increase in actual holding, but the revised method of operation will allow for a much smoother transition to holding when traffic bunching, LVPS, airfield maintenance etc makes this necessary.
Outside the peak hours a freeflow system will be used, which should allow more direct routings and less penalising descent restrictions (e.g. for EDI arrivals there is no requirement to be FL70 level at TARTN during freeflow).
Even in STACKFLOW controllers may offer more direct routeings, if this fits with the prevailing traffic flow. For instance, a GLA arrival to Runway 05 from TRN may be routed directly towards the centrefix, even if STACKFLOW is in use (Incidentally, the TRN STAR for GLA does include LANAK, the plate states "at the discretion of Glasgow ATC aircraft may be instructed to hold at LANAK").
Flexibility is the key to the future operation of the Scottish TMA. A well structured and standard system is required to cover the peak flows of traffic, with a less rigid system to cover off-peak hours. This flexibility should balance the requirement for a safe, orderly and expeditious flow of traffic against the need for operators to fly in the most economical way possible.
Last edited by Talla Radar; 2nd Dec 2008 at 12:20.