Introduction

A recent incident has highlighted the need for Air Traffic Controllers to remain vigilant to the possible consequences of aircraft transmitting an erroneous Mode A code (‘0607’), despite the threat of such occurrences continuing to decrease as more aircraft are modified.

A conflict between two aircraft was aggravated because one of the aircraft involved transmitted an erroneous Mode A code ‘0607’, with no Mode C information, which caused the ATC STCA (STCA) system to become inhibited. The lack of mode C information does not appear to be related to the ‘0607’ problem and is currently under investigation. The conflict was resolved by Airborne Collision Avoidance System (ACAS).