https://hackaday.com/2019/06/09/gps-and-ads-b-problems-cause-cancelled-flights/
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.
With a GPS failure, ADS-B won’t transmit a position. In this case, it is a class of GPS receivers with the issue, mainly Rockwell. A failing GPS will prevent some aircraft from flying if there isn’t a backup system on the MEL, but ADS-B failing at this point just means that ATC needs to revert to secondary radar, big whoop. This affected some air carrier and business Jets with the Rockwell equipment. It is a software bug in the equipment, not the GPS system itself. Most all of GA is unaffected. Once again the referenced hackaday link comments miss the mark.
The non-precision approach current outage map is showing degraded service all over the US Eastern seaboard, as well as the North. The cause of this signal degradation is currently unknown.
This is not abnormal. It is RAIM for NPA without Baro aiding. I don’t know of any GPS that uses RAIM without Baro Aiding and for those using a WAAS GPS, RAIM is not used. Note that there were no outages of RAIM with Baro aiding for NPA. So there is absolutely nothing wrong with the GPS signal and it is not degraded,
From the peanut gallery:
Could be something as mundane as a satellite malfunction or something as nefarious as a state level attack to see how much disruption they can cause. I doubt that it’s ground based given the affected area, but I’m sure some three letter agencies are all over this.
Wrong. It is a software bug in the receiver, a corrupted download.
This isn’t a simple matter of routine degradation. WAAS accuracy has been compromised. WAAS is the basis for ADS-B. Without WAAS accuracy, the reported traffic location can’t be trusted. It’s the Achilles heel of the new ADS-B collision avoidance system.
Wrong. WAAS accuracy and integrity has not been affected or compromised. Wrong the Airlines for the most part are not using WAAS.and their C129 position sources are supplemented with other sensors such as DME-DME and INS, but when the GPS software fails, the supplement isn’t enough. Wrong, the ADS-B collision avoidance system does not exist, TCAS II is used for that.
I could go on, but it is a waste of effort
The GPS almanac update this week included a leap second. This has caused certain Collins GPS units to go into a loop which is unrecoverable. If you don’t turn them on this week the next almanac uploaded by the Coast Guard this Sunday will apparently fix it. It was the interaction between the leap second and a bug in the software. It appears as ADS-B fail on many CAS systems but the loss of ADS-B is not the problem, they have lost GPS nav.
The advantage for the affected aircraft is that most will have had DME-DME so they can still operate in RNAV mode on their FMS.
From Collins: Our team has determined the cause and confirmed that a software calculation of UTC time for the week of June 9, 2019 to June 15, 2019 causes a reset condition, resulting in loss of the GPS function. This condition will no longer occur as the GPS constellation transitions into a new week on June 16, 2019 at 0:00 UTC.
