A publication of the National Air Traffic Controllers Association
Issue link: http://natca.uberflip.com/i/1016075
The factors a ffecting the TF design were determined to be the FMS design bank for the flyby, the number of flybys turns used to emulate the RF, and the distance of turn anticipation for each flyby turn. The interplay among all of these factors will determine the possib ility of an overlay but will not be definitive in terms of the "goodness" o r robustness of the TF overlay. Mike had designed a spreadsheet to explore the impacts of each of the design factors which he demonstrated and also shared with the WG members. Disc ussion of the criteria for a successful overlay revolved around how well the TF track needs to emulate the RF. In general, the tracks cannot be made coincident because each flyby turn will be constructed with a bank angle greater than that required to trav erse the RF, so there will be bank angle changes as the aircraft follows the flyby design track, resulting in differences between the two particularly between the flyby fixes. Consensus was that we will need to define a quantitative measure of the "closene ss" of the two tracks and a maximum difference that can be allowed (what is acceptable to ATC, etc.). Regarding RF applications that could stress any TF design, it was agreed that any application with multiple RFs in sequence, whether they have the same radius or not, could be very difficult and/or risky to emulate using flyby fixes. Turn reversals, i.e., a left RF followed immediately by a right RF, would be in the same cate gory. We might consider a blanket recommendation that in such RF instances a TF design would not be allowed. Atmospheric conditions, e.g., wind speed and direction in particular, will affect groundspeed, and even in conditions where the RF is unaffected, discontinuities i n the TF designs could result. We will likely have to limit th e overlay to RFs of a certain radius or larger to prevent possible wind induced discontinuity in the TF track. 3 . Design Bank Limit for RNP<1: Closed. Submitted to AVS - 1 July 31, 2018. 4 . Intermediate Segment Length: Closed. Submitted to AVS - 1 July 31, 2 018. 5. Outstanding Issues List Review: Mike walked the WG through the 2018 remaining issues list to discuss / choose another issue or two to work on prior to the Q4 F2F. The issues list was updated to show closure of the latest recommendations sent to AVS - 1. The WG agreed to add two of the outstanding issues to the 2018 work plan; the goal is to have final recommendations after the Q4 F2F for: 1. Use of block altitudes on departures (SIDs) and 2. STAR terminus altitudes (when not connected to an approach, the y are sometimes lower than the start of the approach which does not play well in the FMSs). Another item which the group is interested in working is the difference between the standard method of doing obstacle evaluations for approaches and the method u sed for RNP AR. If the two preceding issues can be resolved, the group will begin to address this issue.