US officials argue industry can help satellite ATM advance

Washington DC
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Pressured by civil aviation interests to intensify their efforts to make space-based air traffic management (ATM) a reality, US government officials respond that the aviation industry too has major responsibilities in advancing use of the technology.

Prime among the ways in which the aviation industry can assist the US government in developing satellite-based ATM to operational fruition is in making sure users equip their aircraft early, says Volpe Transportation Research Center engineer Karen Van Dyke.

“The industry needs to support the government by equipping,” she declared today at an Air Traffic Control Association symposium on space-based ATM.

But some industry figures do not agree, arguing that it is more the responsibility of the US government to persuade the civil aviation industry of the business benefits of equipping their aircraft for satellite navigation than it is for the industry to equip in an informational vacuum.

“In itself the industry can do little to push this peanut uphill,” says the Air Transport Association’s vice president for ATM, Jack Ryan. “The government asks, ‘When are you going to equip?’ But there’s an obligation on [both] the government and industry – the government first – in this chicken-and-egg.”

Ryan proposes a solution. “The government needs to hold some industry days soon to report on its operational evaluations of [the] Safe Flight 21 [program]. It needs to talk to operators so they can recognize advantages, then agree on an installation date and codify it through an NPRM (notice of proposed rulemaking). In my personal opinion, voluntary equipage doesn’t work.”

The FAA’s associate administrator for research and acquisition, Steve Zaidman, argues that this is not entirely fair. “There has to be some recognition that applications evolve,” he says. “The industry has to be a little more formal as a group in its business decisions. There needs to be additional business-case thinking from the industry.”

Most importantly from the FAA’s viewpoint, says Zaidman, the US civil aviation industry needs to focus on how it will handle in equipment terms the transitional period from traditional ATM methods and technologies to the space-based ATM navigation and communications technologies now rapidly nearing fruition.

He says the most difficult problem for the FAA in making the move from traditional ATM to space-based ATM is that, “the industry also includes, for us, the military and general aviation”.

Zaidman declares: “That’s the hardest part for us. There is no single requirement and single ability to pay [for use of the system]. There is no single, one-size-fits-all treatment by equipage.”

But Van Dyke believes that, by inaction, the navigational equipment manufacturers have been making the job of the FAA – and other agencies internationally - in developing satellite-based ATM more difficult.

She says the manufacturers have dragged their feet on development of new GPS receivers to take full advantage of the US government’s decision to remove the deliberate timing error from the GPS signal in 2000. The US government had formerly overlaid this varying error on civil GPS signals to make it impossible for potential enemies to use GPS for positional data to guide weapons accurately against US targets.

Van Dyke explains that the control circuits for existing civil aircraft GPS receivers, built to the TSOC 129 technical standard, are hard-wired to apply automatically a 33m pseudo-range error to average out the deliberate selective availability (SA) error.

The SA error makes it impossible for a GPS receiver to provide positional data accurate enough to use GPS for precision landing approaches, one of the most important future tasks for any space-based ATM system.

Another problem, she says, lies in the receiver manufacturers’ short-sighted decision not to develop new aviation GPS receivers until the FAA proves that the signal integrity of its Wide Area Augmentation System (WAAS), a nationwide GPS signal augmentation system, is sufficient to allow aviation operators to use WAAS for precision navigation.

Van Dyke says the software in each existing TSOC 129 receiver includes the receiver autonomous integrity monitoring (RAIM) algorithm that constantly checks the integrity of the GPS signal. However, if the TSOC 129 receiver’s RAIM function determines the GPS signal has lost integrity, it automatically turns the system off, making the aircraft unable to use GPS for precision navigation.

Now there are new technical design standards, TSO 145 and TSO 146, for GPS receivers that on one hand do away with the 33m pseudo-range error and on the other do not turn the receiver off if its RAIM function detects a loss of signal integrity.

Instead, the receiver software determines which of the several signals from different GPS satellites has lost integrity, and automatically excludes just that signal. In almost all cases loss of signal from just one satellite will not be critical enough to affect the receiver’s overall position-calculating accuracy, says Van Dyke, “so you can isolate the faulty satellite and continue navigating”.

But despite these GPS receiver design advances, manufacturers have done nothing yet to incorporate them into actual receiver designs. She believes this is a poor business decision by the manufacturers, particularly when trying to win sales of their GPS receivers internationally.

“If you have RAIM, there is nothing more you need – there is no need to wait for WAAS to be commissioned,” says Van Dyke.