The F-35 stealth fighter does not have a remote kill switch, but it does have the MDF

Due to the shift in US foreign policy, reports have emerged about a possible F-35 kill switch.

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The Pentagon denies rumors about an alleged F-35 kill switch

The information spoke about the possibility that the United States could remotely disable another country's F-35, rendering it inoperable if the US government did not want that country to be able to use the aircraft for a particular mission. These fears are possibly related, in part, to Portugal's cancellation of its purchase of the F-35 and Canada's announcement that it will seek alternatives to that fighter jet, reducing the fleet of F-35s it had planned to acquire.

Following those two announcements, which occurred on Thursday and Friday of last week, respectively, yesterday the official F-35 program Twitter channel posted a message linking to a Flight Global article in which the US Department of Defense denies rumors about this supposed kill switch: "There is no kill switch. The programme operates under well-established agreements that ensure all F-35 operators have the necessary capabilities to sustain and operate their aircraft effectively."

That Twitter post has been shared by Lockheed Martin, the manufacturer of the F-35, with a message stating: "The F-35 is designed to enhance interoperability among allied nations, protecting their sovereignty and ensuring they can operate effectively together to achieve common defense goals."

The MDF, the system with which the US can degrade the capabilities of an F-35

These messages will provide reassurance to many F-35 operators, but that reassurance is not complete. It is true that the F-35 does not have a remote kill switch, but it does have the MDF (mission data files). The purpose of those files is explained in a 2014 document from the Pentagon's Office of the Director of Operational Test and Evaluation (DOTE):

The F-35 relies on mission data loads – which are a compilation of the mission data files needed for operation of the sensors and other mission systems components – working in conjunction with the system software data load to drive sensor search parameters and to identify and correlate sensor detections of threat radar signals. The loads will be produced by a U.S. government lab, the U.S. Reprogramming Lab.

On March 11, an American defense website The War Zone (TWZ) published an article by Joseph Trevithick and Tyler Rogoway stating the following about MDFs:

It’s this mission planning data package that is a major factor to the F-35’s survivability. The ‘blue line’ (the aircraft’s route into an enemy area) that is projected by the system is based on the fusion of a huge number of factors, from enemy air defense bubbles to the stealth and electronic warfare capabilities of the aircraft, as well as onboard sensor and weapons employment envelopes and integrated tactics between F-35s and other assets. To say the least, it is one of the F-35’s most potent weapons. Without it, the aircraft and its pilot are far less capable of maximizing their potential and, as a result, are more vulnerable to detection and being shot down.

The MDF, the system with which the US can degrade the capabilities of an F-35

The article added that MDFs are processed through ALIS (Autonomous Logistics Information System) and its successor, ODIN (Operational Data Integrated Network). TWZ noted that MDFs "rely on work done in facilities located in the United States that are governed by U.S. policy." Tyler Rogoway noted on Twitter on March 10: