Inertial Reference Systems and GPS Spoofing: Honeywell Sets the Record Straight

Spoofing has become a serious concern recently for flight crews operating in the Middle East. In more than 50 cases since August, spoofers have maliciously broadcast fake GPS signals causing airliners and business jets to drift off course. One of the affected aircraft came perilously close to entering Iranian airspace without permission.

Multiple cockpit alerts warn pilots of GPS position jumps so they can get back on track using inertial reference system (IRS) technology, which is not affected by GPS spoofing or signal jamming.

But that is not the story being told in some news accounts and online forums. 

Inertial Reference Systems are Unaffected by Spoofing

“Honeywell wants to set the record straight and assure operators and pilots that inertial data is unaffected by loss of GPS signals or GPS spoofing during flight,” said Ryan Supino, Vice President and General Manager for Navigation Systems at Honeywell.

“Modern navigation systems use both GPS and IRS technologies to enable precise and reliable navigation,” he continued. “Systems like the Honeywell Air Data Inertial Reference System (ADIRS) can provide cockpit systems and pilots with either pure inertial navigation parameters or hybrid parameters that fuse inertial and GPS navigation data.”

During normal operations, the flight management system (FMS) uses GPS or hybrid IRS-GPS as the primary source of aircraft position data. When the GPS signals are spoofed, the FMS position may be driven to the false GPS position and pilots are alerted to the discrepancy between the FMS position and other sensor position such as GPS, radio and/or pure IRS. Even though the pure IRS position is correct, fight crews may interpret the discrepancy as a problem with the IRS.

In addition, most aircraft experiencing these issues also have a navigation radio interface to the FMS.  The radio bearing or distance info is not affected by the spoof, although some reports have indicated that radio navigation was unavailable. It’s more likely that the FMS position was shifted by the spoof and the auto-tuning function was unable to find an appropriate nearby navaid.  Updating the FMS position to the pure IRS position would correct that issue. 

Honeywell Looks to the Future of Spoofing Threats

“The Honeywell hybrid IRS-GPS navigation solution already has some resilience to GPS spoofing,” said Simon Innocent, Commercial Navigation Offering Director at Honeywell. “As spoofed measurements diverge from expected inertial-GPS hybrid values, the system will reject the GPS measurements and begin using inertial data exclusively.”

Tests show that the Honeywell LASEREF VI IRS maintains integrity and rejects a spoofed GPS position shift of three nautical miles over a six-minute exposure time and a shift of 60 NM over 60 minutes. This performance may vary depending on actual spoofing conditions and GPS receiver behavior.

Honeywell is preparing for more sophisticated spoofing threats in the coming years, Supino said. “Our new algorithms will reject spoofed GPS position shifts of 0.2NM for more than six minutes, and position shifts of 3NM for over 60 minutes. The ADIRS will also alert the FMS and flight crews when spoofing is detected. This represents breakthrough improvement.”

This new technology is expected to certify on a commercial air transport platform beginning in 2025. It will also become available on Honeywell’s industry leading LASEREF VI IRS in the second half of 2025.