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Winter Weather Forecasts and Their Effects on Air Traffic Management Spencer Mell -CWSU Met. WFO EAX Winter Weather Seminar 10/27/09. The FAA and NWS. FAA Viewpoint – Weather is like any other traffic. It occupies space in the NAS and generally needs to be separated from other traffic.
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Winter Weather Forecasts and Their Effects on Air Traffic Management Spencer Mell-CWSU Met. WFO EAX Winter Weather Seminar 10/27/09
The FAA and NWS FAA Viewpoint – Weather is like any other traffic. It occupies space in the NAS and generally needs to be separated from other traffic. NWS “bread and butter” products for FAA concerns 1) CCFP – During convective season. 2) TAF’s - Main product used during winter weather season (Oct-Mar).
Types of Winter Weather That Impact the Terminals • Convective Hazards • Winter Precipitation - snow and ice removal - runway conditions/breaking action - snow/fzra/fzdz on aircraft surfaces cause deicing delays. • Wind direction and speed - decides runway usage which affects Airport Acceptance Rate. • Cigs/Vsbys
What do These Winter Weather Delays Mean? • 24% Thunderstorms – CCFP, TAF • 69% Winter Precipitation, Winds, Cigs/Vis - These numbers indicate that many winter weather elements, which occur at the hubs can be the source of delays and “bottlenecks”.
Snow and Icing Conditions • Snow/FZRA/FZDZ - Causes runways to be slick and icy affecting breaking action of landing aircraft. Longer runways (if available) and slower speeds must be used to allow for safe landing. This lowers the airports arrival rate. - Causes runways to be closed for snow removal. - Creates conditions where aircraft need to go through deicing procedures before departure.
Impacts Due to Winter Weather and Icing • The FAA and Airport Authority regulates air traffic when runways have reduced breaking action. • The FAA and Airport Authority regulates air traffic when runways need to be closed for snow removal. • Airlines and the Airport Authority can spend tens of thousands of dollars on deicing aircraft on just one snowy day. There are also environmental issues and expenses involved in collecting deicing fluid.
Mitigating Effects of the TAF • Mitigating effects of the TAF - If FAA and the Airport Authority know the time of onset, intensity, and duration of precipitation they can allocate resources appropriately to remove snow. - If the tower chief has the most accurate information as to the onset and duration of icing conditions we can help reduce delays and expenses due to deicing aircraft.
Impacts Due to Winds • Impacts Due to Winds - runways are built to take advantage of local climatologically favorable winds. When winds come from a less favorable direction or a wind shift occurs traffic management has to “reorganize” traffic to land in a different direction which could cause delays. • Mitigating Effects of the TAF -When tower chiefs and traffic managers are aware of an impending wind shift they can minimize delays and maintain capacity by easily switching their runway configuration.
Reduced Cigs/Vis • Impacts of Reduced Cigs/Vis - Aircraft must land using Instrument Flight Rules (IFR) approach when cigs/vis are below Visual Flight Rules (VFR). An IFR approach spaces the aircraft farther apart as they land using an Instrument Landing System (ILS) reducing airport arrival rate. -Pilots that are not certified to fly in IFR conditions or aircraft that are not equipped to land in IFR conditions must land at an alternate airport with VFR conditions.
Impacts of Reduced Cigs/Vis • Economic Impacts – Estimated $6.5 billion in 2000 - Commercial Airliners have to carry extra fuel in case they have to reroute, hold or divert to an alternate airport. GA pilots must carry enough gas to reach an alternate airport determined pre-flight when cigs are below 2000ft. - When airlines have to land at an alternate destination significant costs can be incurred from terminal fees, food and lodging for crews, expenses for new crews to be brought in to complete the flight. - Customers incur costs related to lost productivity, food and lodging expenses, higher airline prices and cargo shipping rates. • Safety Impacts – On average 440 people die in aircraft accidents per year most due to reduced cigs/vis.
Mitigation Effects of the TAF • Accurate cigs/vis forecasts can allow commercial airlines to use appropriate equipment and crew for the conditions, thus minimizing costs of extra fuel and alternates when possible. • Accurate forecasts can keep GA pilots out of dangerous situations for which they may not be equipped.
Additional Thoughts on the TAF • Given the safety and economic concerns the temptation when writing the TAF may be to err on the side of caution. This, however may cause extra economic costs or if forecasts are consistently pessimist forecasts may result in reduced confidence by the user. The best approach is to forecast as accurately as possible. • When there is uncertainty in the forecast be sure to convey that in the AFD. • The first 6 hours of the TAF are the most critical to aviation operations. • When conditions stray from forecast conditions in the TAF amend early and as often as necessary.
When TAF Coordination Should Take Place • TAF coordination will occur between ZKC CWSU and WFO EAX for the 18Z and 00Z TAFs when: - Cigs at or below 1000ft - Vis at or below 2SM - Wind speed of 13kts of greater - Thunderstorms, freezing precipitation or an inch or more of snow. • Collaboration for the 18Z TAF will normally be for the first 12 hours of the TAF and the first 13 hours of the 00Z TAF. • Unscheduled coordination should occur when a TAF needs to be amended.
Airport Acceptance Rate (AAR) • Airport Acceptance Rate – The Number of aircraft that an airport can accommodate for landing during a given time frame. • Depends on: 1) Layout of the airport – number, length, and separation of runways.
MCI Runway AAR • Runways 19R/1L and 19L/1R - 52 • Runways 19R/1L and 19L/1R during ILS approach - 38 • Runway 27/9 or other single runway configuration - 26
What is an ILS Approach? • Instrument Landing System or ILS - is a ground based instrument approach system used during IFR conditions that provides precision guidance to aircraft approaching and landing on a runway using a combination of radio signals and in many cases high intensity lighting arrays to ensure a safe landing.
ILS Categories • Category 1 – decision height not lower than 200ft, visibility not less than 2500ft, or a runway visual range of not less than 1800ft. • Category 2 – decision height lower than 200ft but not lower than 100ft, and a RVR not less than 1200ft.
ILS categories cont’d • Category 3a – A decision height of less than 100ft or no decision height and an RVR not less than 700ft • Category 3b – A decision height no less than 50ft or no decision height and an RVR not less than 150ft. • Category 3c – No decision height or RVR. * In each case a suitably equipped aircraft and qualified crew are required.
Airport Arrival Demand • Airport Arrival Demand – Refers to the number of aircraft destined for an airport over some time interval.
When Demand Exceeds AAR • When the demand exceeds AAR the Traffic Management Unit can handle that by activating any of these programs at the terminal. - Ground Delay program - Ground Stop program - Special Traffic Management program
Ground Delay Program (GDP) • Ground delay program (GDP) – TMU manages air traffic by limiting departures to an airport where the projected traffic demand is expected to exceed the airports AAR for a lengthy period of time. -Most common reasons for reduced AAR is adverse weather such as unfavorable winds, low cigs/vis. - Limits airborne holding which saves fuel costs and increases safety *TMU does not use GDP’s for MCI
Ground Stop Programs • Ground Stop (GS) – requires that aircraft not meeting categorical criteria remain on the ground. • GSs are one of the most restrictive methods of traffic management and are used: - In severely reduced capacity situations such as cigs/vis below most user minimums and runways closed for snow removal. - To avoid extended periods of airborne holding. - Preclude sector/centers from reaching saturation levels. - In the event a facility is unable to perform ATC services. - When routings are unavailable due to severe weather. *GSs are often issued progressively making accurate TAFs very important to TMU.
Special Traffic Management Programs (STMP) • Special Traffic Management Programs (STMP) – Special procedure to accommodate abnormally large traffic demands. - Generally used by ZKC for GA traffic coming into the area for special events or major sporting events. * TAFs are important in scheduling “appointments”.
