Trajectory Specification For High-Capacity Air Traffic Control

Russ PaielliNASA Ames Research Center

AIAA ATIO-06 ConferenceWichita, KS, Sept 27, 2006

[paper available at http://RussP.us/publist.htm]

2

Outline

• Motivation• Trajectory prediction• Trajectory specification

– Error tolerances and bounding space– Horizontal and vertical specifications– Polynomial approximation

• XML• Concluding remarks

3

Motivation

• Demand for domestic air travel expected to double or triple within ~20 years

• Airspace capacity currently limited by controller workload (~15 aircraft/sector max)

• Automated separation assurance can increase airspace capacity

• 4D trajectories can facilitate automated separation assurance

• No standard currently exists for specifying and communicating continuous 4D trajectories with error tolerances

4

Trajectory Prediction

5

Trajectory Specification

6

4D Trajectory Specification

• Not just a series of 4D points!• 3D fixed tube with position along tube as fourth

dimension• Groundtrack composed of straight (great circle)

segments and constant-radius turns (2D)• Altitude as function of along-track distance (third

dimension)• Along-track position as function of time (fourth

dimension)• Error tolerances determine bounding space

around reference trajectory

7

Trajectory Error Tolerances

• Explicit along-track/cross-track/vertical tolerances• Conformance required with high reliability• Can vary with traffic situation

– Limited by navigation capability of aircraft– Looser tolerances in light traffic

• Determine a precisely specified bounding space for each aircraft at each point in time– Useful for automated separation assurance

• Disabled vertical and/or along-track bounds reduce dimension of specified trajectory– could be useful for early implementation

8

Advantages of Explicit Bounding Space

• Enhanced fault tolerance– Conflict-free trajectories can be guaranteed

for given time horizon even if ground systems and/or datalink fail

• Maximize airspace capacity– Particularly useful in weather-constrained

areas– Comparable to painting lane lines on roads

9

Capacity EnhancementIn Weather-constrained Areas

10

Misunderstandings to AvoidAbout Trajectory Specification

• Does not imply centralized “control”– But facilitates centralized coordination– Can be used to downlink trajectory requests

or uplink trajectory assignments• Does not mandate “precise” tracking of 4D

reference trajectory– Precisely specifies bounds on aircraft

position at any point in time– Bounds can be large when appropriate

11

Horizontal Trajectory Specification

• Two segment types– straight (greatcircle)– turn (circular arc)

• Each segment defines own coordinate system

• Along-track/cross-track tolerances define bounding space

• Along-track updates compensate for wind modeling errors

12

Vertical Trajectory Specification

13

Problem With Altitude As Function Of Time

14

Leveloff Transition Tolerance

15

16

17

Why XML?

• Text format less error-prone and more flexible than binary format– Directly readable by engineers/developers– Flexible selection and ordering of data fields

• Replacing binary formats in many domains– e.g., B2B, SVG, OpenDocument, MS Office

• Independent of computer platform and programming language

• Versatile, popular, standardized

18

XML Sample

<segment number="1" vtype="climb" htype="straight" stype="constCAS"> <time start="0:08:42" duration="7:42"/> <begin lat="xxx.xxxx“ lon="xxx.xxxx"/> <end lat="xxx.xxxx“ lon="xxx.xxxx"/> <along coeffs="xxx.xxx xxx.xxx" CAS="280" length="27.815"/> <alt coeffs="126.8 21.609 4.1417e-3" thrust="90" end="270" /> </segment>

19

Concluding Remarks

• 4D trajectory specification– 3D tube with position along tube as fourth

dimension– Error tolerances define bounding space at

each point in time– Facilitates automated separation assurance

and resulting increased airspace capacity• XML is a strong candidate for the job

– Versatile, popular, standardized• Lead time for establishing and implementing

standards is very long -- no time to waste!