2000-2001: Official Reports of Unexplained Airliner Transponder Jamming, Military Exercises A Suspected Cause

Just prior to the September 11 attacks - between November 2000 and April 2001 - French aviation authorities noted and investigated repeated instances of unexplained commercial airliner Mode S transponder jamming resulting in the loss of secondary radar data to Air Traffic Control (ATC). Affected aircraft included Air France Boeing 767s.


Three of the four reportedly hijacked September 11 flights also stopped providing secondary radar data to ATC via Mode S transponders during their flights. These Mode S transponder data losses were officially attributed to manual deactivations by alleged hijackers, although evidence to confirm this claim was never cited by the 9/11 Commission Report. September 11 flight transponder data losses contributed significantly to a circumstantial impression of alleged hijacker flight deck takeovers and also coincided with significant nationwide US military exercises that day.


Thanks for continuing to document things like this.

...The disappearances could happen at any time; day, night, week day or week-end.
The phenomenon suddenly reappeared between the 21st and the 26th March 2001 and then again between the 13th and the 26th April 2001... ...Globally, these events put the operational services into sensitive situation because the label disappearances did not affect all aircraft and their random nature caused stress and uncertainty to controllers... ...At least two of these incidents could have been serious....