Environmental Optimization of Aircraft Departures: Fuel Burn, Emissions, and Noise (2013)

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78 D-1. Introduction The acronym Noise Abatement Departure Procedures (NADPs) is used to describe actions taken to minimize or reduce aircraft operational noise in the neighboring commu- nities in the vicinity of the airport. Although typically applied to define the vertical profile (engine thrust and aircraft configuration management) during the initial climb it can also be applied to other noise mitigation measures such as curfews/restrictions and restricted ground paths or tracks when departing an airport. At noise sensitive airports it is quite common for the air- port to have negotiated with surrounding neighborhoods to achieve acceptable departure ground tracks. These agree- ments are enforced by the airport through departure clear- ances issued by the airport traffic controllers (ATC). While some of these agreements include dispersing the departures with divergent headings (fanning) others include minimal departure tracks to prevent over-flight of specific areas. With the projected growth in air traffic, the FAA’s Next Generation Air Transportation System (NextGen) is com- mitted to capacity increases while reducing the environ- mental impact of operations for both noise and emissions. The presence of minimal ground paths can negatively affect runway(s) departure capacity or throughput. One method of increasing the runway departure capac- ity is the implementation of divergent heading departures. A modeling analysis of this methodology is presented to support the expected capacity gains and benefits associated with this departure procedure. However, it should be noted that such studies are highly dependent on the specifics at each airport. D-2. Overview The ATC procedures for departures are contained in Chap- ter 3, Section 9 of the FAA JO 7110.65. Departing aircraft are classified in four categories: HEAVY, B757, LARGE, and SMALL (See Table D-1). All aircraft require an in-trail sepa- ration or spacing of 3 nautical miles (NM) while within the TRACON airspace with the exception of the HEAVY and B757 classes which require a separation of 5 NM and 4 NM respectively due to wake turbulence concerns. This wake turbu- lence distance separation translates to a 2-minute time separa- tion before trailing aircraft can receive a departure clearance (See Table D-2). The minimum separation requirement is then stretched to the 5 NM minimum in-trail separation required in the Air Route Traffic Control Center (ARTCC) airspace which is approximately 40 NM from the airport. It is not uncommon for an ARTCC, with high-density traffic to request 7 NM separations to facilitate existing traffic while transitioning departures to the en-route phase. D-3. Divergent Heading Departures The FAA Joint Order 7110.65 (Chapter 3, Section 9) defines the departure separation requirements. As stated, if the minimum separation requirement can be assured, a depar- ture clearance for Category III aircraft can be issued after the preceding aircraft has reached a point 6,000 feet down the runway and a visual confirmation of rotation (nose gear off the runway) is made. Initially, divergent heading depar- tures required a minimum heading change of 15 degrees and ground radar confirmation of the course change. Currently, divergent heading departures are relying on the airborne capability of RNAV-equipped aircraft to execute a defined departure route containing the required heading change. D-4. Modeling of Divergent Heading Departures SIMMOD PRO! was used to produce a comparative model analysis of a straight-out in-trail departure versus a diver- gent heading departure. SIMMOD is an industry standard analysis tool used by airport planners and operators, airspace A P P E N D I X D Noise Abatement Departures and Runway Throughput Analysis

79 designers and ATC authorities for high-fidelity simulations of both airport and airspace operations. The SIMMOD model also includes an animator which provides a detailed view of simulated aircraft operations both on the ground and airborne. D-5. Model Design Several factors can affect the implementation of divergent heading departures—the airport and runway configuration, ground traffic crossing the active departure runway, the air- craft fleet mix, and the departure schedule. These factors render any modeling effort only applicable to the conditions modeled. Given that the analysis was for runway departure optimization, the following design and inputs were used: • The airport design chosen was a parallel runway configu- ration with the terminal/gates between the runways elimi- nating the need for traffic crossing the active runway. • The fleet mix included all four separation classes; HEAVY, B757, LARGE, and SMALL. • The departure schedule was intentionally made unrealisti- cally high (120 departures, departing at 30-second inter- vals) to ensure that the departure queue was full for either scenario (divergent and non-divergent). D-6. Model Inputs Available aircraft performance data was used to determine the distance and altitude associated with a typical depar- ture profile and this data was used for the SIMMOD input requirements for the aircraft model INITIAL_DEP and LOW_ CLIMBING departure segments which required a speed input (Minimum, Nominal, and High). Since the initial climb-out speed (V2) varies by airport elevation, airframe type, weight, and temperature; a sea level airport elevation was assumed and the speed for a nominal takeoff weight was chosen. Available aircraft performance data was also used to deter- mine the input for takeoff roll distance. Since the minimum distance for Category III aircraft is 6000 feet and confirmed rotation, a 7000 foot roll was assumed for all modeled air- craft which introduces a somewhat conservative factor in the model results. The SIMMOD model default departure separations were removed, and iterative runs of the model were made to deter- mine the departure spacing required to result in the mini- mum aircraft separations given in Table D-2. It should also be noted here that the separations used were applicable to Visual Meteorological Conditions (VMC). Using the SIMMOD Ani- mator, the actual separation for each iteration was checked by measuring the separation when the trailing aircraft was over the end of the departure runway (See Figure D-1). The divergent departure routing incorporated a heading change (turn) initiated approximately 1 nm off the end of the depar- ture runway. Both the non-divergent and divergent model scenario analysis was for the same 120 aircraft comprised of 50.8% Heavy, 15% B757, 19.2% Large, and 15% Small with the iden- tical departure schedule. To assess the influence of fleet mix, an additional model scenario was run with the HEAVY air- craft replaced by B737-800s and the B757 aircraft replaced with EMB 145s, producing a schedule of 70% LARGE, and 30% SMALL. Again, for the additional model the identical departure schedule was used. D-7. SIMMOD Results Two metrics were used to assess the benefits of the divergent heading departure methodology; Departure Queue Time and Departure Rate. Taxi times were not considered representative AIRCRAFT TYPE CLASS A300, A330, A340, B747, B767, B777, DC10, MD11 HEAVY A318, A319, A320, A321, B727, B737, MD80, ERJ170, ERJ195, FOKKER F50, FOKKER F100, CRJ700 LARGE CRJ100, CRJ200, GA-PROP SMALL B757 B757 Table D-1. Aircraft categories. TR A IL IN G A IR CR A FT LEADING AIRCRAFT HEAVY B757 LARGE SMALL HEAVY 4 nm 4 nm* 2.5 nm 2.5 nm B757 5 nm* 4 nm* 2.5 nm 2.5 nm LARGE 5 nm* 4 nm* 2.5 nm 2.5 nm SMALL 6 nm 5 nm 4 nm 2.5 nm * Wake Turbulence Requirement Table D-2. Wake turbulence separation.

80 since the departure schedule was non-realistic and inflated to produce a departure queue for each scenario. Full Fleet Mix - Non-Divergent versus Divergent: • Departure Queue Reduction – 13.79 minutes (9.8%) improvement. • Runway Departure Rate – 5.59/hour (10.88%) improvement. The additional scenario for an assessment of the influ- ence of fleet mix compared the non-divergent departure sce- nario with a full fleet mix and a fleet mix of only LARGE and SMALL aircraft. This comparison produced the following results and supports the earlier statement that the fleet mix does impact runway capacity. Non-Divergent – Full Fleet Mix versus No Mix: • Departure Queue Reduction – 6.6 minutes (4.7%) improvement. • Runway Departure Rate – 2.49/hour (4.8%) improvement. D-8. Current Activities and Conclusions RNAV departures with a divergent heading of 10 degrees are currently being demonstrated at Atlanta Hartsfield- Jackson airport. Although no published results are currently available, discussions with Atlanta TRACON report that using the divergent headings for departures off of two run- ways has resulted in an increase of 8 to 13 departures per hour. This report is in good agreement with the results of the SIMMOD modeling discussed above. The significance of the reduced divergent heading departure (10 degrees versus the current 15-degree minimum requirement) could enable some noise-impacted airports to apply the procedure and still avoid over-flights of existing noise sensitive areas. As such, the use of a divergent heading departure method can result in increases of runway capacity or throughput. Again, this demonstration was provided for illustration only. Airport capacity assessments are dependent on the specific opera- tions, layout, etc. of each airport. Figure D-1. SIMMOD animator.