A real‐time frequency‐shift decoder for the last transmission of Korean Airlines flight 007

Abstract

On 1 September 1983, Korean Airlines flight 007 was intercepted and destroyed by a Soviet jet fighter after straying into Soviet airspace. Although the flight recorder from KAL 007 was not recovered, its final transmissions were recorded at a Tokyo air traffic control center. The intelligibility of the KAL 007 transmissions is compromised by at least three types of distortion: broadband background noise, narrow‐band noise tone, and frequency‐shift distortion. This paper describes a DSP system that has been developed to counteract the frequency‐shift distortion. The system employs Hilbert transform‐based techniques to introduce a linear compensating frequency shift, the extent of which may be controlled manually by the user or automatically by a separate computer. Tests performed to date with the system on the KAL 007 transmissions have shown it to be a useful tool. Intelligibility improvements have led to independently verified advances in understanding several of KAL 007's final transmissions.