A flight key was a device used by United States Air Force drone pilots to authenticate themselves within the computer system. Before a pilot could take control of a drone, they had to insert the flight key into a specific slot in the console and use a biometric fingerprint scanner to provide their credentials. Flight keys also served as storage devices, recording the actions and keystrokes of the owner while they operated the drones and also the drone's flight data.
During Day 9, First Lieutenant Chris Tanner's drone was hacked and used to attack an U.S. military convoy in Kajaki Province, Afghanistan. Tanner's flight key was part of the evidence and according to Captain Greg Denovo, it confirmed that the attack indeed came from Tanner's console.
Later, Tanner was taken to the United States Embassy in London, along with the flight key, for further investigation. Jack Bauer infiltrated the embassy in order to recover the flight key which he needed to gain a proof that Tanner's drone was hacked. Jack located the room which Tanner was being held in where he was under the guard of Captain Greg Denovo. Jack knocked out Denovo and asked Tanner where was the key. Tanner told him that Denovo had it, and after checking his pockets, he took it and plugs in Tanner's flight key to the secure communications room's terminal for Chloe to check the data. Due to a slow upload, Cross told Jack that he sent a software program to handle the encryption. Unfortunatly, the Marines storm the room under orders of President Heller and the upload is stopped. However, Kate Morgan comes to believe Jack's story and secretly takes the flight key to get the needed proof. Afterwards, Kate contacted Chloe to continue the upload. Once Kate got to her laptop in her vehicle, she plugged the flight key into the USB port and the download automatically resumed. Chloe and Adrian see a override code on the program and Kate transmits this new evidence to Jordan Reed, clearing Tanner and proving Bauer's story. President Heller immediately orders the drone fleet grounded, but Al-Harazi gains control of six of the ten drones she wants before he can succeed. ("Day 9: 3:00pm-4:00pm")