Center for Advanced Aviation System Development Interval Management A Brief Overview of the Concept, Benefits, and Spacing Algorithms Dr. Lesley A. Weitz Principal Systems Engineer The MITRE Corporation, Center for Advanced Aviation System Development MIT Lincoln Laboratory Air Traffic Control Workshop 5 December 2017
Content 2 IM Concept Overview Why IM? IM Air and Ground System Components IM Applications and Operations Path to Deployment
IM Concept Overview 3 Enabled by ADS-B In, Interval Management (IM) will facilitate more precise inter-aircraft spacing IM avionics onboard an aircraft will provide speed commands to the flight crew to achieve an Assigned Spacing Goal relative to a Target Aircraft IM is a tactical spacing tool ATC provides the spacing goal, which can be based on a metering schedule, miles-in-trail restriction, applicable separation standard, or any other operationally-needed spacing objective Improves spacing consistency by enabling more frequent trajectory adjustments than possible with a ground system alone More precise spacing can be translated into increased arrival throughput NASA
General IM Procedure 4 ATC utilizes ground automation capabilities to pre-condition arrival flows 1. Assisted by ground automation, ATC determines IM aircraft pairs and desired spacing goals 2. ATC communicates Target Aircraft identification and IM initiation parameters to the IM Aircraft flight crew Spacing Goal = 80 seconds FAA 3. Flight crew of IM Aircraft enters the information into IM avionics 4. When IM execution requirements are met, IM avionics provides IM Speeds for flight crew to fly to achieve and/or maintain desired spacing 5. Flight crew follows the IM Speeds and ATC monitors until termination IM Arrival and Approach Same Runway Example
Why IM? The Relationship Between Inter-Arrival Time Variability and Throughput
Spacing Tool Domain Why Interval Management? 6 Spacing management tools can be: Ground based (i.e., ATC automation) Flight-deck based (i.e., specialized avionics functions) Spacing applications can be classified as: Absolute crossing a point in space at a specified time (e.g., an STA) Relative crossing a point in space with a specified interval after another aircraft Ground Based Flight-deck Based STA #2 Min Separation Relative Spacing Interval Absolute TBFM, GIM-S, TSAS RTA STA #1 ATA #1 Type of Spacing Relative Radar-based Separation, CRDA, MIT Visual Separation, CAVS, IM Absolute Spacing STA = Scheduled Time of Arrival ATA = Actual Time of Arrival Min Separation Relative Spacing
7 Defining Performance Metrics Inter-arrival Time (IAT) o Time elapsed between two consecutive aircraft crossing a common point (e.g., the Final Approach Fix or runway threshold) Mean o The average value of a set of observations o A measure of the central tendency of a distribution Standard deviation o A measure to quantify the amount of variation or dispersion of a set of data values (i.e., the spread of the numbers) o For normally-distributed data: o 68.2% of the observation will be within one standard deviation of the mean ( 1 sigma ) o 95.4% of the data will be within two standard deviations ( 2 sigma ) Mean IAT Sigma (1 sigma) ~95% Performance Bound (2 sigma)
8 Benefits of Flight-deck Spacing Capability Benefits are determined by: Translating improvements in runway precision (IAT sigma) into capacity (arrival/departure) curves for an airport Using the new capacity curves in a system-wide model to quantify delays at different points in the flight Capability IAT Sigma (sec) No metering (baseline) 18.0 En-route Metering Only 16.5 En-route and Terminal Metering 12.0 1 Interval Management 5.0 2 Terminal Metering = Terminal Sequencing and Spacing (TSAS) Notes: 1. Measured performance at the Final Approach Fix as determined from TSAS Human-in-the-Loop (HITL) experiments. 2. Required performance at the Final Approach Fix per the FIM MOPS (DO-361). Picture from NASA ATD-1 ConOps
How Does IAT Sigma Impact Throughput? The Math 9 IAT Sigma = [5.0, 12.0, 16.5, 18.0] seconds Assumptions: IMC, No gaps in flow to the runway Minimum time-based spacing at FAF = 53 seconds* Spacing Goal IAT Sigma = 18.0 sec: 94.8 sec (41.8-sec buffer ) IAT Sigma = 16.5 sec: 91.3 sec (38.3-sec buffer ) IAT Sigma = 12.0 sec: 80.8 sec (27.8-sec buffer ) IAT Sigma = 5.0 sec: 64.6 sec (11.6-sec buffer ) Spacing Goal Assumes controller will need to intervene in 1% of operations Spacing goal = Min time-based Spacing at FAF + 2.32 x IAT sigma 2.32 factor shifts the distribution to ensure that only 1% of operations fall below min spacing Throughput = 3600 sec/hr Mean Spacing [sec] Throughput IAT Sigma = 18.0 sec: 38.0 ac/hr IAT Sigma = 16.5 sec: 39.4 ac/hr IAT Sigma = 12.0 sec: 44.5 ac/hr IAT Sigma = 5.0 sec: 55.7 ac/hr * Assumes a 2.5-NM separation and a 170-kt groundspeed (i.e., near the FAF)
Throughput (ac/hr) How Does IAT Sigma Impact Throughput? Based on Equipage Rates 10 The throughput improvement is related to the equipage rate in a mixedequipage environment 56 54 52 50 48 With ground-based tools alone: IAT Sigma = 12.0 sec Difference in STAs = 80.8 sec Throughput = 44.5 ac/hr With IM avionics: IAT Sigma = 5.0 sec Spacing Interval = 64.5 sec Throughput = 55.7 ac/hr 46 44 0 10 20 30 40 50 60 70 80 90 100 IM Equipage Rate (%)
Incremental Throughput Benefit of IM over TSAS (ac/hr) How Does IAT Sigma Impact Throughput? Varying the Minimum Spacing Value 11 13 12 53-sec min spacing 11 10 9 8 7 6 5 4 3 50 60 70 80 90 100 110 120 Minimum (Time-based) Separation Assumption (sec)
IM Air and Ground System Components
IM Arrival Management System Components 13 Air: ADS-B In, including IM avionics Current Flight-deck IM (FIM) standards: DO-328A and DO-361 Some IM applications may require data communications Ground: ERAM and STARS: interface to the controller TBFM: Traffic preconditioning and IM scheduling, initiation, and monitoring
IM Avionics Operational Behavior 14 Primary objective of the IM avionics: achieve and/or maintain a desired spacing relative to another aircraft Achieve Stage: Speed guidance to work toward the desired spacing at a desired location (the Achieve-by Point) Maintain Stage: Speed guidance to hold the desired spacing between the IM and Target Aircraft based on current states Time that IM Aircraft crosses the Achieve-by Point Time that Target Aircraft crosses the Achieve-by Point IM Tolerance time Spacing Interval Assigned Spacing Goal The spacing interval is measured along the path
IM Sample Algorithm Achieve Stage 15 Achieve Stage control law is a function of predicted 4D trajectories for the IM and Target Aircraft Inputs to trajectory modeler: navigation procedure, forecast winds, and aircraft states Trajectories are generated using a kinematic trajectory modeler Outputs: predicted flight times to the Achieve-by Point from current states Achieve Stage Control Law After crossing the Achieve-by Point, algorithm transitions to the Maintain Stage, which uses a different control law
IM Sample Algorithm 4D Trajectory Generation 16 Kinematic trajectory generator uses generic aircraft performance parameters Trajectory logic respects constraints on Performance-based Navigation (PBN) Procedures Altitude and Speed constraints Trajectories are built backwards from the last point using a series of trajectory segments Idle Descent, Constant Airspeed Idle Descent, Constant Mach Idle Descent, Deceleration Constant Geo Flight-Path Angle Descent, Constant Airspeed Constant Geo Flight-Path Angle Descent, Deceleration Level Flight, Constant Airspeed Level Flight, Deceleration Altitude behavior Speed behavior The kinetic trajectory represents what an aircraft s FMS would compute Trajectory accuracy is primarily a function of aircraft modeling and wind forecast errors
IM and Ground-based Automation 17 En route and terminal tactical IM operations may be possible with nothing more than an indication of IM equipage on the controller display During metering operations, requirements for ground automation are being designed to perform the following functions: Precondition arrival flows for increased probability of successful IM Operations Account for IM and Target Aircraft capability when building an arrival schedule Identify aircraft pairs and clearance information elements Determine initial feasibility of the IM Operation Generate a clearance appropriate for the communications medium (i.e. voice or DataComm) Provide IM initiation and monitoring information to the controller(s), including when the IM and Target Aircraft are in different sectors Monitor IM operational feasibility; if conditions change, either suggest a clearance amendment to the controller or recommend that the operation be terminated
IM Applications and Operations
IM Applications (1 of 3) Same Runway and IM Cruise 19 IM Arrival and Approach (Same Runway) En route through terminal: to a single runway during metering operations (~TOD to no later than the final approach fix) Ground automation schedules IM capable aircraft closer than it would otherwise IM operations can start before aircraft are on common routes, though IM and Target routes must be common at last waypoint Ground automation sets up feasible IM operations based on ETAs to the Achieve-by Point Aircraft are on RNAV routes with altitude and speed constraints (4D trajectory) IM Cruise Used in en route airspace during Miles in Trail (MIT) operations Reduce the number of speed or vector instructions controllers need to issue to aircraft to meet MIT restrictions Single Runway Arrival and Approach with terminal area merge
IM Applications (2 of 3) Dependent Staggered Approaches (DSA) and Dependent Converging/Crossing Runways (DCCR) 20 DSA: increase arrival throughput for dependent parallel runway operations by allowing an IM Aircraft to manage its spacing relative to the aircraft landing on the parallel runway DCCR: potentially enable certain ATC facilities to consider lowering the weather minima (i.e. ceiling and visibility to which the operation can be conducted) and/or increase operations to the secondary runway. Full implementations will require TBFM dependent runway scheduling
IM Applications (3 of 3) Paired Approach (PA) 21 Objective: Increase capacity of closely spaced parallel runways (i.e., runways closer than 2500 feet and as close as 700 feet) when visual approaches cannot be conducted IM avionics provide IM speeds to keep the IM Aircraft in the Safe Zone 700 ft d < 2,500 ft d Characteristics Enables terminal area operation based on proposed Paired Approach Separation Standard Avionics functionality similar to DSA, though alerting and tighter spacing tolerance may be necessary Ground tools will likely be required to monitor conformance to the separation standard
Path to Deployment
Path to Deployment in the US 23 Process for deploying the IM concept in the US National Airspace System Develop a Concept of Operations (ConOps) Defines the roles and responsibilities of the human actors and how they interact with automation/avionics Develop and publish IM Avionics Standards Defines the minimum requirements on the avionics Develop the Requirements Document for the ATC Automation Systems Conduct Human-in-the-Loop studies to inform and validate the concept and automation/avionics requirements Cost/Benefit Analysis and Acquisition Secures the funding for the changes to the ATC Automation Systems Need to show sufficient benefits to outweigh the costs Conduct Operational Benefits Validation Partner with an airline to equip a subset of their fleet Conduct IM Operations with revenue flights over approximately one year We have already made significant progress on many of these steps!
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Thank you! Questions? This work was produced for the U.S. Government under Contract DTFAWA-10-C-00080 and is subject to Federal Aviation Administration Acquisition Management System Clause 3.5-13, Rights In Data-General, Alt. III and Alt. IV (Oct. 1996). The contents of this document reflect the views of the author and The MITRE Corporation and do not necessarily reflect the views of the FAA or the DOT. Neither the Federal Aviation Administration nor the Department of Transportation makes any warranty or guarantee, expressed or implied, concerning the content or accuracy of these views. 2017 The MITRE Corporation. All Rights Reserved. Approved for Public Release. Distribution Unlimited.
Backup
IM Avionics Standards 27 IM Avionics Standards are developed through RTCA RTCA is a non-profit organization that brings together government agencies and industry stakeholders to develop standards collaboratively IM Avionics Standards include: Input/Output (I/O) requirements Internal processing requirements Test procedures and test vectors A sample algorithm that meets the requirements Flight-deck Interval Management (FIM) Minimum Operational Performance Standards (MOPS) (DO-361) published Nov 2015 Same runway applications, federated avionics DO-361A being developed now target completion Q2 FY20 Adds dependent runway applications, integrated avionics
IM Avionics IM Clearance Information 28 To initiate and execute an IM operation, ATC needs to communicate the following information to the flight crew:* IM Clearance Type (e.g., Achieve-by then Maintain vs. Capture then Maintain) Target Aircraft ID Assigned Spacing Goal Achieve-by Point (when applicable) Target Aircraft Intended Flight Path Information (IFPI) Planned Termination Point (may be defaulted) Target Aircraft IFPI can be specified as a combination of the following: Same route (as the IM Aircraft) Direct-to a named waypoint Named route (e.g., a RNAV STAR or approach) *Additional IM Clearance elements are needed for dependent runway operations, but are not detailed here
A-IM and Data Link Services Overview 29 Basic IM operations are possible with voice communications Data communications simplify the process of IM clearance delivery enabling: Benefits of IM to be extended to more complex airspaces and routings More efficient maneuvers from more accurate Target Aircraft trajectory predictions IM use of Data Comm may include: Complex IM Clearances requiring several elements (via CPDLC) Target Aircraft IFPI determined dynamically (e.g. defining a route as sequence of waypoints or lat/longs) (via CPDLC) ATS Winds system provides common winds picture (via AOC Uplink Message/ARINC 702A)
IM Avionics Algorithm Functionality and Equipage 30 IM Avionics algorithm is predictive (i.e., based on predicted 4D trajectories for both IM and Target Aircraft) IM Speeds are relative to a nominal speed profile (limited to ±15% of the nominal speeds and based on procedural speed constraints) Target Aircraft s winds can be derived from IM Aircraft s winds or be provided separately Target Aircraft s IFPI must be sufficiently constrained with altitude and speed constraints to ensure a reasonable prediction of the Target s trajectory in the algorithm Retro vs. Forward Fit Avionics Retrofit: Not integrated with other flight-deck systems (e.g., FMS, flight guidance, or Data Comm systems), flight crew implements IM Speeds manually and ensures that aircraft is able to meet altitude constraints on the RNAV procedures Forward Fit: avionics integrated with data communications, FMS, and flight guidance systems
31 Proposed IM Automation Builds Build 1 voice only; limited ground system capabilities (ERAM and STARS CHI for equipage indicator and operational state) Limited Arrival & Approach applications Cruise applications Build 2 voice only; TBFM, ERAM, & STARS enhancements Arrival & Approach with metering and initiation prior to merge point Build 3 DataComm Arrival & Approach with dynamic routing and ATC Winds Arrival & Approach with Improved Target Aircraft IFPI and ATC Winds (yields more efficient IM Operations) Note: each build includes all of the capabilities of the previous build
Other IM-Related Activities 32 IM Performance Assessment Team (IMPAT) Multi-organization team (FAA, MITRE, NASA, JHUAPL, MIT-LL, etc.) of modeling and simulation experts Addresses technical challenges that arise in various IM activities and related to ATC automation integration NASA Advanced Technology Demonstration-1 (ATD-1) Flight Test Flight Test occurred in January/February 2017 Results demonstrated that IM avionics can provide precise inter-aircraft spacing in a realworld environment Results and lessons learned informing avionics standards development ANG-C22 Paired Approach (PA) Demo Flight Demo planned for early CY2019 IM team is providing IM concept and avionics standards expertise