GPS and ADS-B Problems Cause Cancelled Flights in USA [hackaday.com]:
Something strange has been going on in the friendly skies over the last day or so. Flights are being canceled. Aircraft are grounded. Passengers are understandably upset. The core of the issue is GPS and ADS-B systems. The ADS-B system depends on GPS data to function properly, but over this weekend a problem with the quality of the GPS data has disrupted normal ADS-B features on some planes, leading to the cancellations.
Automatic Dependent Surveillance-Broadcast (ADS-B) is a communication system used in aircraft worldwide. Planes transmit location, speed, flight number, and other information on 1090 MHz. This data is picked up by ground stations and eventually displayed on air traffic controller screens. Aircraft also receive this data from each other as part of the Traffic Collision Avoidance System (TCAS).
ADS-B isn’t a complex or encrypted signal. In fact, anyone with a cheap RTL-SDR can receive the signal. Aviation buffs know how cool it is to see a map of all the aircraft flying above your house. Plenty of hackers have worked on these systems, and we’ve covered that here on Hackaday [hackaday.com]. In the USA, the FAA will effectively require all aircraft to carry ADS-B transponders by January 1st, 2020 [faa.gov]. So as you can imagine, most aircraft already have the systems installed.
The ADS-B system in a plane needs to get position data before it can transmit. These days, that data comes from a global satellite navigation system. In the USA, that means GPS. GPS is currently having some problems though. This is where Receiver autonomous integrity monitoring (RAIM) comes in. Safety-critical GPS systems (those in planes and ships) cross-check their current position. If GPS is sending degraded or incorrect data, it is sent to the FAA who displays it on their website. The non-precision approach current outage map [faa.gov] is showing degraded service all over the US Eastern seaboard, as well as the North. The cause of this signal degradation is currently unknown.
Hundreds or even thousands of flights have been cancelled. Teleconferences with the FAA (Federal Aviation Administration) conducted. Fllights are restricted to fly only up to 28,000 feet. What's going on? Is GPS under attack?
As time went on and more reports came rolling in, it became clear that the problem reports were limited to aircraft flying with certain GPS receivers [rntfnd.org]:
A corrupted upgrade to a large class of receivers was to blame for what was initially suspected to be a degradation of GPS service across much of the United States (see FAA graphic).
Work by the FAA and industry groups revealed that many Rockwell Collins receivers had received a bad update. See: AIN Online “Collins GPS Receivers Suffer Reception Outage [ainonline.com].”
The more that companies try to squeeze the last bit of income out of any kind of system or product, the closer the tolerances become and they seem to be tolerant of disruptions.
How close are we to the point of "peak optimization" where any profits from additional refinements are countered by systems being more brittle and thus more expensive to operate in challenging conditions?