“A U.S. E-6B Doomsday Plane is using ‘Trump’ as radio callsign while flying over central U.S. right now” blared the headline on a Flipboard Magazine story in early March.

At the World Economic Forum in Davos, Switzerland, in January, a group of reporters for the Quartz website put together an ADS-B receiver and tracked all the helicopter traffic flying to and from the conference, then reported what they discovered.

Aircraft for which blocking of position data has been requested are regularly seen on the ADS-B Exchange website, which does not comply with blocking agreements that are supposed to protect blocked aircraft information. “This cannot possibly be called ‘progress,’” wrote a commenter on a popular business aviation forum earlier this year, frustrated that his own airplane can easily be tracked despite his participation in the FAA’s blocking program.

“Currently, several sources of crowd-sourced flight-tracking information are making business aircraft movements extremely easy to track by reading the mode-S transponder code,” NBAA noted in a survey that it sent to members on March 16. The one-question survey asked members to comment on how often they would be willing to change the hexadecimal code on mode-S transponders in their aircraft to prevent such simple tracking of their movements.

The latest Senate bill on FAA reauthorization includes language that would attempt to fix the blocking dilemma. The new legislation, according to NBAA, “ensures the real-time location of general aviation aircraft is not disseminated or displayed, protecting the privacy and security of flight information.”

Blocking of information about aircraft flying in U.S. national airspace has become difficult, despite the FAA’s current blocking program. This program, which replaced the previous Block Aircraft Registration Request (Barr) system, relies on flight-tracking providers’ agreeing to block information at operators’ requests in exchange for being able to tap into the FAA’s Aircraft Situation Display to Industry (ASDI) data feed.

The problem with blocking is that simple sub-$100 hobbyist receivers can detect position, speed and identification information by receiving broadcasts from mode-S transponders and ADS-B out transmitters. None of this information is in any way encrypted, and hobbyists can share the information gathered on their receivers to create a network of flight-tracking information. Flight-tracking companies can also use information from receivers, as does FlightAware with its PiAware receiver and Passur with its own receiver network, but FlightAware, Passur, FlightRadar24 and others participate in the agreement to withhold information on blocked aircraft.

Not so ADS-B Exchange. This website was put up by pilot Dan Streufert last year. “This is really just a hobby,” he told AIN. “I got interested in aircraft tracking with PiAware and found that I could expand on that. I threw the site up for the heck of it.”

In Streufert’s opinion, there is little that can be done to protect the information that aircraft are broadcasting about their position. “The information is being broadcast in the clear over the air,” he said. “Any sense of security that operators may have had is an illusion. If you have a mode-S transponder, you can be tracked. ADS-B makes it a bit easier. The information is already out there, just spend $100 on Amazon to buy the parts and you can receive it. If the bad guys want the information, it’s already out there. We’re not making anything that is not already there. Maybe it will draw attention [to this situation]. Even military aircraft are trackable on mode-S. There are a ton of military aircraft on the site, including Air Force One, U-2s, and they’re perfectly trackable.”

Security Concerns and Protecting Information

The business pilot who complained about being unable to block his airplane on ADS-B Exchange is worried about the security implications of someone with ill intent tracking his airplane and others. He asked not to be identified for this article, and AIN agreed to withhold any information that might identify him. He also believes the unblocked information could be used by businesses tracking competitors’ activities, to thwart, say, the purchase of one company by another. “There is an [airplane] at my airport in the [unidentified] business, and it goes to a place in [another state]. They’re only going for one reason: there is a store for sale and they want to buy it. [Now] it’s simple for the competitors to go and see what’s for sale,” he explained.

There are efforts under way to prevent identifying aircraft from airborne transponder and ADS-B broadcasts, possibly encrypting those signals, and to enact laws regarding the dissemination of such information.

Section 609 of a House FAA reauthorization–which failed to make it through Congress, likely because of its ATC privatization focus–included language that would require the FAA to block aircraft upon request. S.2658, which was approved by the Senate Committee on Commerce, Science and Transportation on March 16, eliminates the privatized ATC proposal and essentially replicates Section 609 of the House bill with a “Right to Privacy When Using Air Traffic Control System” amendment proposed by Sen. Dan Sullivan (R-Alaska): “Notwithstanding any other provision of law, the Federal Aviation Administration shall, upon request of a private aircraft owner or operator, block the registration number of the aircraft of the owner or operator from any public dissemination or display, except in data made available to a Government agency, for the noncommercial flights of the owner or operator.”

This appears to address concerns about blocking registration information, but receivers could still detect mode-S transponder or ADS-B out signals and, presumably, view the real-time position of even blocked aircraft, in contrast to NBAA’s wording in its survey question. The bill’s language also doesn’t cover blocking of military or commercial aircraft.

NBAA says it is aware of the concerns of its members and is working on several avenues to provide relief to operators that don’t want their aircraft to be so easily trackable. Part of this includes the survey that the association sent on March 16, but there are other efforts under way as well.

At a December 2015 meeting of the industry Equip 2020 group, according to Jens Hennig, vice president of operations for the General Aviation Manufacturers Association (GAMA), the FAA explained how dynamic allocation of 24-bit addresses could work. Currently these addresses are listed on the FAA registry for each mode-S-equipped aircraft and also a database for RVSM-equipped aircraft and enable flight-tracking services to look up that information. Changing to an address not linked to the registry would essentially make a tracked aircraft unidentifiable, except by a spotter positioned near an airport using a pair of binoculars, a zoom lens or the naked eye to view registration numbers.

At the meeting, the FAA asked NBAA to develop a concept of operations for how dynamic allocation would work for its members, including, Hennig explained, how many operators would use it, how often the addresses would be changed and the number of aircraft that would be affected. The FAA also wants to know whether transponders would need to be altered to allow dynamic allocation. “Can the address change be made through a menu setup or do we need to add a capability?”

A better way to block could be encrypting the 24-bit address, which would eliminate the need to change it. The FAA has asked the RTCA Program Management Committee to see if this would be feasible and practical, according to Hennig, although this would be a longer-term project.