A software design error that misinterprets GPS time updates is the root cause of Collins Aerospace GPS and multi-mode receiver malfunctions, the manufacturer has advised aircraft operators.

The receiver malfunctions, first reported by operators on June 9, affected multiple Collins-equipped airliner and business jet types. A number of regional and mainline carriers in the US canceled flights, including Missouri-based LCC GoJet Airlines, Phoenix-based Mesa Airlines, Ohio-based PSA Airlines and Utah-based SkyWest, according to FAA.

The agency identified Bombardier CRJ regional jets and Boeing 737-900 narrowbody airliners, specifically, as experiencing problems.

On June 13, the National Business Aviation Association (NBAA) said it “continues to monitor the ongoing service disruption” involving Collins GPS receivers, advising business jet operators to familiarize themselves with the systems on their aircraft.

“This is a rapidly evolving situation, and the NBAA Air Traffic Services team is seeing the nationwide operational effects from this disruption from the FAA’s Air Traffic Control System Command Center,” NBAA director for air traffic services and infrastructure Heidi Williams said.

“We continue to be engaged with the FAA, Collins Aerospace, aircraft manufacturers and other affected stakeholders to determine the best route forward in resolving these complications,” Williams added.

The FAA Command Center initially approved a blanket waiver allowing affected carriers to fly below 28,000 ft. and requiring them to file flight plans based on area navigation routing if possible or traditional ground-based navigation aids.

In a notice obtained by Aviation Week Intelligence Network, Collins explained to operators that a regularly scheduled GPS almanac update with a “leap second” caused GPS-4000S sensor and GLU-2100 multi-mode receiver (MMR) malfunctions. Almanac position data transmitted by satellites helps accelerate “time-to-first-fix,” the time required for a navigation receiver to acquire satellite signals.

Software timing calculations by the devices “have reacted to this leap second by not tracking satellites upon power-up and subsequently failing,” Collins stated, which confirmed issuing the notice.

The loss of GPS navigation also affects the position source used for automatic dependent surveillance-broadcast signaling, something FAA will require for all aircraft operating in US airspace by January 2020.

Collins said the next scheduled GPS almanac update is June 16. “We do not believe this update will include time information which triggers this error, however, we are testing for impact of this almanac update,” the manufacturer added.

The GPS-4000S, integrated with Collins Pro Line 4 and Pro Line 21 avionics systems, supports use of GPS as a primary means of navigation within Satellite-Based Augmentation System coverage. The GLU-2100 MMR supports use of instrument landing system, GPS, GPS landing system and VOR navigation aids.

Bill Carey bill.carey@informa.com