Committee Corner
News from ALPA's Committees

ADS-B+CDTI—A New Way to Track Traffic

NASMOD Committee

By Jan W. Steenblik, Technical Editor
Air Line Pilot,
October 2004, p.27

Air traffic control delays are back, costing the U.S. airline industry billions of dollars per year and adding to the already heavy burden of difficulties with which the industry is now struggling. Airport and airspace capacity constraints have once again become critical.

The need to modernize the U.S. National Airspace System (NAS) has never been greater, although the FAA’s budget that is allocated to NAS modernization (NASMOD) has been slashed dramatically since 2001.

Facing this daunting challenge are the 60 pilot safety representatives of ALPA’s NASMOD Presidential Committee organized into Project Teams, who have been participating in a multitude of government/industry advisory groups and other forums to help set the priorities for the FAA’s multiyear, multibillion-dollar NASMOD effort.

Part of that multifaceted effort is Safe Flight 21, a joint government/industry effort to improve the safety, efficiency, and capacity of the NAS by using Automatic Dependent Surveillance-Broadcast (ADS-B), a surveillance technology that allows pilots and controllers to have a common picture of airspace and traffic.

First Officer Ed Rafacz (Delta), leader of ALPA’s ADS-B Project Team, points out that ADS-B "is considered a cornerstone enabler for ‘Free Flight,’ the NASMOD goal of flight with minimal ATC restrictions."

In August, he and Capt. Alan Campbell (Delta, Ret.), a longtime ALPA pilot safety representative, met with Capt. Jim Walton of UPS’s Advanced Flight Systems Department, at SDF (Louisville, Ky.) for a briefing on UPS’s progress. They flew jumpseat to outlying UPS stations and back to SDF to see the cockpit display of traffic information (CDTI) in actual line operation.

ADS-B is part of a proposed surveillance system through which an equipped aircraft or ground-based vehicle will transmit information to all receivers. This information will include an aircraft’s call sign, GPS position, velocity, and closure rate to other aircraft and to ATC, thus allowing for common situational awareness to all appropriately equipped users.

The primary objective of the Safe Flight 21 program is to demonstrate nine enhancements that will facilitate Free Flight capability: Air-to-air use of ADS-B is expected to (1) permit safely reducing aircraft separation standards, (2) improve low-visibility approaches, and (3) enhance see-and-avoid and (4) enroute operations. On the ground, ADS-B could (5) improve navigation on taxiways, (6) enhance controller management of surface traffic, and (7) minimize runway incursion and (8) landing and traffic conflicts.

ADS-B can also (9) provide surveillance coverage in nonradar airspace, as demonstrated during the Capstone project in Alaska. Capstone is currently providing advisory control in "nonradar" areas using radar separation criteria and is expanding coverage to southeast Alaska. Embry-Riddle Aeronautical University is equipping its fleet to provide flight following and management benefits. Australia will install an ADS-B-based surveillance coverage that will augment its current radars and open the rest of that continent up to positive control.

A related-technology traffic information system-broadcast (TIS-B) and flight information system-broadcast (FIS-B) can offer an affordable way to reduce controlled flight into terrain, and display weather by uplinking the data to the cockpit. This reduces weight and on-board computing requirements.

A key component is the CDTI display of traffic information that displays other ADS-B traffic, terrain, weather, own-ship information and location, and other information. It also allows pilots to determine distance to traffic, and includes a moving-map display of airport-surface maps, which are now under development. Whenever two ADS-B-equipped aircraft on the same link are in range of each other, they will be displayed on the CDTI.

UPS has equipped its B-757s and B-767s with a CDTI that integrates ADS-B data and TCAS II. FAA-certified for "enhanced visual acquisition," the CDTI helps UPS pilots flying into their company’s hub in SDF to locate traffic as they converge during their 2 a.m. push. The UPS pilots use the CDTI to locate traffic but do not refer to the CDTI or ADS-B in voice communications with ATC. In the near future, UPS hopes to begin the next phase of the program—with SDF air traffic controllers, to use the other airplane’s call sign when reporting traffic, moving toward enabling CDTI aided visual separation (CAVS) approaches.

To come: CAVS approaches will allow visual approaches to continue when pilots lose sight of the "aircraft to follow" visually but have acquired that aircraft’s position on the CDTI display. Testing in MITRE’s lab has yielded good responses from pilots. Controllers will use normal visual approach phraseology and procedures; an in-service evaluation in VMC (visual meteorological conditions) is scheduled to begin at SDF in 2005.

ALPA has been involved in this development for many years. This promising technology with its great safety benefits and capacity increases is not without flaws, however; but ALPA’s NASMOD Committee feels they can be mitigated and is working closely with the various airline industry and government groups to ensure that concerns are addressed and fixed. No ALPA carriers are now actively involved mainly because of finances and the FAA’s realignment. FedEx had been set for some limited trials.