In an emergency situation, controllers are always required to use professional judgement and experience to determine the best course of action. Sometimes this causes conflict with rules and regulations that might, in those circumstances, be unfit for purpose. All controllers know that special circumstances call for special measures; indeed, ICAO Doc 4444 and many local manuals make a provision for controllers to do exactly that in emergency situations.

When an aircraft makes an emergency landing or a precautionary landing with associated risks, the aerodrome’s fire brigade is usually on standby at a tactical position near the runway in use. Releasing the runway to the emergency vehicles vis à vis the landing traffic is a time and safety critical operation.

ICAO does not explicitly describe procedures for issuing conditional clearances to vehicles but it has been suggested that those might help in facilitating the expeditious handling of emergencies by aerodrome tower controllers.