Introduction

After the terrorist attacks of 11 September, 2001, Prolonged Loss of Communication (PLOC) events, already a concern in terms of the potential for loss of traffic separation, became a very sensitive issue for security reasons. As PLOC events are often now initially treated as potential security risks, it is important that both pilots and ATCOs are made aware of the problem and its potential consequences.

This article describes the possible consequences of a prolonged (two-way) loss of communication (PLOC) event and suggests defences, best practices and mitigations which could be used by air traffic controllers (ATCOs). However, these are not intended to be exhaustive or automatically applicable and should not prejudice local ATC procedures.