*** Do not use this for flying refer to your AFM and company policy OM ****

Why we should report every single interference.

Leaving spoofing aside for now.

Ever since the summer of 2019 Israeli skies are subject to recurring GPS jamming. Civilian airplanes are required by regulation to be protected against GNSS interference. And therefore are not as OEM do not volunteer to undertake such modifications and design that is not mandatory.

Navigation error.

  •             Cross-track error and flying outside of the airway.
  •             MAP appears to be wrong while following ILS needing the dissonance to be resolved.
  •             It might lead to taxi error on the ground as the airport moving map (as installed) might shift.
  •             Finally, it might lead to runway disagree alerts.


  • GPS alerts
  • ADS-B out Alerts
  • Terrain position alerts

FMC “insufficient fuel” alerts due to clock rewinding.

On a few occasions the airplane clocks stated going backwards. Mostly on 777. This caused insufficient fuel massage leading to a distraction to sort the issue. To rule out fuel leak.

Distractions at low altitude

Coming to land if you have an ADS-B out alert, when you call for landing checklist you will get the ADS-B OUT Non-Normal-Checklist, and if you take your time, you will get a “Checklist incomplete” Alert. All these lead to the PM going head-down at low altitude for prolonged periods of time.

EICAS messages at low altitude after takeoff and even more so an EGPWS warning might lead to dangerous reactions especially at high gross weights after takeoff.

EGPWS false alarms.

On Boeing models and as far as I know some other types, not including Airbus the EGPWS uses GPS present position. There are no Enhanced functions without a valid FPS signal. When the Jamming is intermittent. On occasion the GPS will come back online with erroneous position for a fraction of a second. This is enough that if the erroneous position happens to be in a high elevation area a PULL UP warning will be triggered before the position is correct.

HUD miscue

Boeing uses GPS heading to correct HUD heading. If the flight crossed a significant number of meridians the IRS will accumulate a heading error. They use GPS heading to correct this. If GPS signal is not valid the display will have an error leading the Flight Path Vector not to indicate the actual vector but to have a bias. We found this be the most concerning issue do to the fact that a pilot following the ILS uses the FPV to identify the landing runway, Our risk management indicated the risk of identifying a parallel taxiway as the landing runway. We ended up instructing our pilots to stow the HUD.

Tower is not aware.

The control tower is not always aware that the airplane is experiencing a GPS outage. the airplane at 3000 might be blocked while the control tower at ground level might be jamming free. This lack of information will lead the controllers to assign RNP approaches.

Normalization of deviance

One of the most troubling aspects of this prolonged problem is that we are getting used to flying in a sub-par environment. This is something that will come back to haunt us some day. Getting used to non-normal environment has the potential to lead to us not noticing other threats, I can think of a few examples. We are getting used to false EGPWS warnings some of us ignore them, but someday they might be a real one. We ignore the reputative GPS and ADS-B alerts and might miss a completely different warning. Flying head down at low altitude is never good. Late decision to change to an ILS approach.

CAA is not aware of the magnitude of the problem.

We all know there are times when this happens every single takeoff and landing. In Tel Aviv this might mean 300 movements a day. The CAA thinks this is something that happens 10-20 times a year.

They must be made aware of reality.

We must report every single GPS outage and or interference.

Otherwise no one will do anything to make things better or mitigate the risk.


Stay safe.



Leave a Reply