TERMINAL AIRSPACE ENCOUNTER SET V1.0
====================================

June 30, 2020

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BACKGROUND
==========

The incorporation of unmanned aircraft terminal operations into the scope of Detect and Avoid 
systems necessitates analysis of the safety performance of those systems--principally, an assessment 
of how well those systems prevent loss of well clear from and collision with other aircraft. This 
type of analysis has typically been conducted by Monte Carlo simulation with synthetic, 
statistically representative encounters between aircraft drawn from an appropriate encounter model. 
While existing encounter models include terminal airspace classes, none explicitly represents the 
structure expected while engaged in terminal operations, e.g., aircraft in a traffic pattern. An 
initial model of such operations, scoped specifically for assessment of unmanned aircraft on 
straight-in approach at a Class D airport encountering a second aircraft either landing or taking 
off, has been developed using a Bayesian network framework like other MIT Lincoln Laboratory 
encounter models. In this case, the Bayesian networks have been tailored to address structured 
terminal operations, i.e., correlations between trajectories and the airfield and each other. FAA 
terminal radar track data over 3-8 months in 2015 at 14 single-runway airports throughout the NAS 
have been used to train the model. The model has been sampled to generate a set of one million 
terminal area encounters for use in initial terminal area safety analyses. Development of the model
continues with plans to address additional ownship operations in an expanded set of terminal areas.

ASSUMPTIONS
===========

The following assumptions and limitations of MIT Lincoln Laboratory Terminal Encounter Model (LLTEM)
Version 1.0 should be noted:

    -- Ownship is an unmanned aircraft operating under Instrument Flight Rules (IFR) per DO-365A
    -- Ownship is on a straight-in approach to a Class D airfield
    -- The airfield has a single runway
    -- Arbitrary intruder aircraft may be landing or taking off but not merely transiting the area
    -- Trajectories constrained to within 8 NM of the airfield and 3000 ft above airfield elevation
    -- Trajectories are a maximum of 240 seconds long
    
DATA SET CONTENT
================

This data set consists of trajectories for 1,000,000 encounters sampled from Version 1.0 of the 
LLTEM. All encounters are between two aircraft, where Aircraft 1 is the unmanned ownship on 
straight-in approach. Trajectory data is provided in two forms: a single binary file containing 
position points for all encounters, and full state data (position/velocity/attitude) in individual 
text files for each aircraft and each encounter. An additional file indicates the sampled encounter 
conditions as well as CPA information for each encounter.

1) ENCOUNTER INFORMATION DATA

The file 'terminal_encounter_info_20200630.csv' containts the encounter conditions at closest
point of approach (CPA) for each encounter as sampled from the encounter conditions model. It 
additionally contains the horizontal and vertical separation at CPA and the time CPA occurs 
relative to the beginning of the encounter. This data can be used to filter the encounter set as
desired, e.g, for encounters between landing aircraft only. The file is in comma-delimited plain 
text format with the following columns: 

    (1) Encounter ID
    (2) Airspace class (1 - Class D)
    (3) Ownship intent (1 - landing) 
    (4) Intruder intent (1 - landing, 2 - takeoff)
    (5) Intruder type (1 - fixed wing)
    (6) Intruder runway (1 - same)
    (7) Ownship distance from runway at CPA (in nautical miles)
    (8) Ownship bearing relative to runway at CPA (in degrees)
    (9) Ownship altitude at CPA (in feet relative to airport elevation)
    (10) Ownship speed at CPA (in feet per second)
    (11) Ownship track relative to runway at CPA (in degrees)
    (12) Intruder distance from runway at CPA (in nautical miles)
    (13) Intruder bearing relative to runway at CPA (in degrees)
    (14) Intruder altitude at CPA (in feet relative to airport elevation)
    (15) Intruder speed at CPA (in feet per second)
    (16) Intruder track relative to runway at CPA (in degrees)
    (17) Time of CPA (in seconds)
    (18) Horizontal miss distance (in feet)
    (19) Vertical miss distance (in feet)

2) ENCOUNTER TRAJECTORY DATA
The file 'terminal_encounters_20200630.dat' contains both ownship and intruder trajectory data for
the full set of encounters. This data is the direct output of the TEM trajectory generation models. 

The structure of the binary file is as follows:

[Header]
uint32 (number of encounters)
uint32 (number of aircraft)
    [Encounter 1]
        [Initial positions]
            [Aircraft 1]
            double (along-runway position in feet)
            double (cross-runway position in feet)
            double (altitude in feet)
            ...
            [Aircraft n]
            double (along-runway position in feet)
            double (cross-runway position in feet)
            double (altitude in feet)
        [Updates]
            [Aircraft 1]
            uint16 (number of updates)
                [Update 1]
                double (time in seconds)
                double (along-runway position in feet)
                double (cross-runway position in feet)
                double (altitude in feet)
                ...
                [Update m]
                double (time in seconds)
                double (along-runway position in feet)
                double (cross-runway position in feet)
                double (altitude in feet)
            ...
            [Aircraft n]
                ...
    ...
    [Encounter k]
        ...


3) ENCOUNTER EXTENDED STATE DATA
Each of the encounters has additionally been run in simulation to generate full state data for 
ownship and intruder aircraft. The simulation uses a relatively simplistic dynamics model and flight
controller with the following constraints on the the behavior of both manned and unmanned aircraft:

    -- Maximum airspeed: 250 kt
    -- Maximum airspeed acceleration: 0.25g
    -- Maximum vertical rate: 1000 fpm
    -- Maximum bank angle: 70 deg
    -- Maximum pitch rate: 3 deg/s
    -- Maximum turn rate: 6 deg/s
    -- Maximum roll rate: 30 deg/s

This data is in the 'terminal_encounter_state_data_20200630.zip' file, a compressed archive of 1000 
directories each containing data files for 1000 encounters. The name of each file indicates whether 
it applies to the ownship (unmanned) or intruder (manned or unmanned) and the encounter number. The 
data files are in comma-delimited plain text format with columns as follows:

    (1) Time (in seconds)
    (2) Speed (in feet per second)
    (3) Track Angle (in radians)
    (4) Bank Angle (in radians)
    (5) Pitch Angle (in radians)
    (6) Acceleration (in feet per second squared)
    (7) Along-Runway Position (in feet)
    (8) Cross-Runway Position (in feet)
    (9) Altitude (relative to runway elevation, in feet)
    (10) Along-Runway Velocity (in feet per second)
    (11) Cross-Runway Velocity (in feet per second)
    (12) Vertical Speed (in feet per second)
    (13) Heading Rate (in radians per second)
    (14) Latitude (in degrees)
    (15) Longitude (in degrees)

Latitude and longitude values assume a runway at 42.4699 deg latitude and -71.2874 deg longitude 
oriented due north.

CONTACT INFORMATION
===================

For more information about the data set or to provide feedback, please contact Randal Guendel at 
781-981-5362 or randal.guendel@ll.mit.edu.