Future ADS-B

Doug Arbuckle
Federal Aviation Administration

Bangkok, Thailand 06 November 2018

 Background
• Joint RTCA and EUROCAE effort to update 1090 MHz Extended Squitter
(1090ES) MOPS and the Mode S Transponder MOPS
• RTCA and EUROCAE formed the Combined Surveillance Committee (CSC)
– RTCA SC-186 WG-3 & EUROCAE WG-51 SG-1 (1090ES)
RTCA SC-209 & EUROCAE WG-49 (Mode S Transponder)
• Activity commenced in January 2016; expected completion is December 2019
– ADS-B MOPS re-opened with the primary objective to support the ADS-B IN Advanced
Interval Management application
• Outcomes:
1090ES MOPS update from Version 2, DO-260B/ED-102A, to Version 3 (DO-
260C / ED-102C)
Mode S Transponder MOPS from DO-181E/ED-73E to DO-181F / ED-73F
updating to Mode S Subnetwork version 6
 ADS-B Development
• Support A-IM application
– Add broadcast of additional parameters to support application
– Enhanced receiver to support longer range performance
– Track initiation enhancements to improve track acquisition
• Support High Altitude / High Velocity Vehicles
– ICAO Surveillance Panel agreed to support these vehicle operations on 1090ES,
so CSC is developing support for such vehicles
– New position reporting formats required due to limitations of previous versions to
support high velocity vehicles and range limitations in reporting altitude, velocity
and vertical rate
– Considers FAA recommendations for reporting of altitude, velocity, and vertical
rate in support of future commercial space operations
 ADS-B Development
• Addition of optional Phase Modulation support
– ICAO SP agreed to standardize capability to provide additional
capacity on 1090ES
– expanded data capacity with low spectrum impact
• Phase data is overlaid on pulses of existing signals so no additional occupancy
on 1090 MHz
– Version 3 will define phase encoded messages for ADS-B State
Vector Report and Interrogation/Reply Monitoring (IRM) data

• Removal of UTC Coupled Position Reporting

– In 1090ES, this was known as T=1 position reports
– Did not provide intended benefit and removal reduces complexity
 ADS-B Development
• Downlink Format (DF=19) no longer has subtype assigned to ADS-B
– reserved solely for military use
– previous ADS-B subtype removed so that ADS-B information for civil
authorities do not depend on or expect DF=19 ADS-B data
• GNSS position extrapolation timeout increased to prevent reporting
no position data when a single GNSS update is missed
– Time interval for reporting “No Position” increased from 2.0 to 2.6 seconds
• Changes in processing of Flight ID data so that consistent behavior is
provided in reporting aircraft identification on 1090ES and Mode S via
GICB register extraction by Ground SSRs
 ADS-B Development
• Geometric Vertical Accuracy encoding modified to report
GVA <= 10 meters for the benefit of future ADS-B IN applications
• Geometric Altitude (HAE) reporting improved
– Currently reported as relative offset to barometric altitude
– Version 3 will report HAE independent of barometric altitude
– Expanded range to support higher altitude limit
• Weather surveillance – Aircraft based Observations (AbO)
– includes: gross weight, wingspan, icing, Eddy Dissipation Rate
(EDR), water vapor
 ADS-B Development
• Removal of several Airborne Position Message Type Codes that are no
longer required due to change to report both barometric and geometric
altitudes in version 3
• Addition of optional Interrogation / Reply Monitor (IRM) capability
– Data supports monitoring of 1030 MHz interrogation and 1090 MHz transponder reply
activity
– Provides ANSPs ability to monitor spectrum activity
• Support for ACAS-X (ACAS Xa/o RTCA DO-385 and future ACAS Xu) for
future collision avoidance coordination capabilities
• Support for UAS Detect and Avoid (DAA) systems interoperability with
collision avoidance systems
 ADS-B Development
• Horizontal Protection (HPL) limit for high position integrities
– New requirement provides upper bound for reporting position integrity if position source cannot
account for all error contributions
• Unmanned Aircraft Systems (UAS) Lost Link
– Report new alert when UAS command and control link is lost
• ICAO definition of an associated Mode A Code is proposed
– Broadcast contingency message to report future waypoints when command and control link is lost
• Support of Autonomous Distress Tracking with new alert for indication of Aircraft-in-
Distress
• Update of guidance on reporting selected altitude and selected heading data, especially in
setting of mode control bits defining source and type of altitude and heading information
• Improved algorithm for Air-Ground determination to improve reporting ADS-B
airborne/surface position formats
– U.S. monitoring data shows improper reporting from many aircraft without weight-on-wheels switch
 ADS-B Development
• Indication of Reduced Capability Equipment (RCE)
– TSO-C199 and CAP1391 equipage reporting so that users of ADS-B data recognize
limitation of data from these vehicles
• Surface Link Mitigation Service Status for ADS-B-In-equipped aircraft
– Currently, TIS-B and ADS-R service indications are supported
– ADS-R same-link rebroadcast service indication will be added so that surface
applications are aware that the surface volume provides this service to enhance
surface coverage
• Removal of unused message fields previously broadcast in version 2 or earlier
– NICBARO, TS Report Capability, Trajectory Change Report, Air Referenced Velocity
Report Capability, and Receiving ATC Services are to be removed
 ADS-B Development

• Also under consideration and development:

– Indication that an aircraft is an RPAS
– Emitter Category changes
– ICAO Aircraft Type indication
– ADS-B track prioritization in support of A-IM
 ADS-B Development
Miscellaneous Message Transmission Modifications
– Removal of Event-Driven Squitter Protocol
• Protocol established to limit transmissions in any one second
• Removal based on complexity and changes in message transmission operation that make event-
driven protocol obsolete
– Modified transmission to continuously provide Air Referenced Velocity
• True Heading considered not necessary for broadcast and removal allows increased capacity for
other parameters
– Continuous broadcast of Emergency/Priority Status Message
• 1090ES version 2 terminated message broadcast when Mode A code set to 1000
– Uniform distribution of position message formats
• Change proposed to overcome lack of uniformity in transmitting both position format types
• Selection of format type is determined every second rather than on each position data register
update as specified in versions 0, 1 and 2
• Improves track initiation
 Transponder Development

• Changes to the Transponder MOPS:

– improvements, corrections
– required to reflect ICAO SP agreements
– for consistency with changes to1090ES in updating to version 3
 Transponder Development
• Eliminating reply to Mode A/C/S All-Call
– Reduces spectrum activity
– Prevents use of an interrogation that will no longer be allowed by ICAO after January 2020
• Definition of a Basic Level 2 Transponder
– Reduced functionality to eliminate protocols that support capabilities that are not utilized
– Becomes new ICAO minimum Mode S transponder standard for international civil air traffic
• Basic Dataflash
– Due to concern that Dataflash requires capabilities no longer supported by a Basic Level 2, Basic
Dataflash provides the functionality without the need for a full Level 2 transponder
• Phase Modulation
– Corresponding changes to transponder MOPS to support phase modulation on 1090ES
– Considering phase data on Mode S replies to facilitate multiple GICB register extractions with a
single interrogation and reply
 Transponder Development
• Mode S reply rate limiting
– Implemented to prevent long periods without replying when exceeding transponder reply capability
– Also considering specifying a maximum allowable reply rate
• New requirements for Mode S and ATCRBS transmission signal baseline
– Problems reported by European ground systems detecting Mode S replies
– CW signal level preceding and during reply created detection issues
– No requirements limiting CW during these transmissions so MOPS update will incorporate limits
• Changes to accommodate ACAS-X
– Accommodates ACAS-X capabilities related to coordination, RA reporting, and CA capability reporting
– Updates to provide additional verification of providing highest priority to RA data across ACAS interface
to transponder
• Clarification of reply content when interrogating for GICB registers not serviced
• Support for optional Interrogation/Reply Monitoring
 Transponder Development

• Elimination of interrogation controls for 1090ES rate,

airborne/surface format and antenna selection
• Reply Dead time modification to reduce transponder occupancy
• Removal of acquisition squitter inhibit
• Data Link Capability Register changes
– Support for ACAS X versions, Basic Dataflash and reporting of added
capabilities in this MOPS update
• Various unused registers (51, 52, 5F, F1, and F2) become Reserved