Australia Delays ADS-B Deployment
August 2, 2006
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Australia's privatized air traffic control service delayed deploying
automatic dependent surveillance-broadcast (ADS-B) in lower-level airspace.
The decision, however, does not affect U.S. plans to transition to ADS-B from radar, the Aircraft Owners and Pilots Association (AOPA) said.
"Australia was planning on implementing their ADS-B system differently," said Randy Kenagy, AOPA senior director of advanced technology.
"That creates different issues for ADS-B down under."
ADS-B is an alternative to radar and transponders for air traffic control surveillance.
ADS-B avionics in the aircraft broadcast the aircraft's location (as determined by global positioning systems, or GPS) to the ground and to other aircraft over a datalink.
In the U.S. implementation, the ADS-B datalink also will be used to send free weather and traffic information to aircraft.
General aviation (GA) pilots will be able to see on a multifunction screen up-to-the-minute weather graphics - including weather radar - weather reports and forecasts. They also will be able to see the relative positions of nearby aircraft that are not transmitting ADS-B on the datalink.
In Australia, media reports indicated that ADS-B could be "spoofed" - someone with a laptop computer and the right transmitter could supposedly add hundreds of fake ADS-B targets to a controller's screen.
According to AOPA, some observers say the press reports played a role in the decision. The official reason for the delay, according to Airservices Australia, however was that implementing ADS-B for lower-level airspace "raises a number of operational and policy issues that require resolution before a decision to proceed can be made."
AOPA says spoofing does not pose much of a concern in the U.S., both for technical and regulatory reasons. The U.S. Federal Aviation Administration (FAA) plans to require ADS-B infrastructure to include a validation function, which means there must be an independent way to ensure that ADS-B targets are legitimate.
The FAA also selected universal access transceiver (UAT) as the ADS-B datalink for general aviation. Australia chose the 1090-MHz Mode S extended squitter system as its ADS-B datalink. Mode S extended squitter does not have nearly the data capacity of UAT, according to AOPA.
"The UAT datalink has more than enough capacity to send weather and traffic information back to the pilot," said Kenagy. "Also, it's technically easy to validate - and harder to spoof - a UAT transmission."
The UAT validates information by looking at the GPS location report and seeing if that data makes sense compared with a position derived from calculating the time it takes for the signal to travel from the aircraft to the ground receiver.
Validation of the Mode S ADS-B system is possible as well, but it's unclear to some in the industry as to how Australia was planning to ensure that an ADS-B position was legitimate.
AOPA questions, however, if spoofing is even a big issue given the fact that spoofing air traffic controllers is not a widespread problem and has not wreaked havoc on the air traffic control system.
"It's easier said than done," said Kenagy, "and pilots and controllers are pretty good at recognizing a problem and working around it."
Source: Aircraft Owners and Pilots Association (AOPA).