Conditional Clearances to Rescue and Firefighting Vehicles

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Conditional Clearances to Rescue and Firefighting Vehicles

56TH ANNUAL CONFERENCE, Toronto, Canada, 15-19 May 2017

WP No. 86

Conditional Clearances to Rescue and Firefighting Vehicles

Presented by TOC


This paper examines the status of the conditional clearance and the question of whether extending their range to rescue and firefighting (RFF) vehicles may help in facilitating safer and more expeditious handling of emergency situations. The paper concludes that conditional clearances might be of use in these circumstances but should be subject to the strictest standards of implementation and use.


1.1 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 (ICAO Doc 4444, Chapter 15, Section for controllers to do exactly that in emergency situations.

1.2 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.

1.3 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. Therefore, it was determined that TOC should examine the utility and feasibility of conditional clearances for rescue and firefighting (RFF) vehicles.


Conditional clearances

2.1 A conditional clearance is a clearance issued to an aircraft subject to conditions under which the instruction must be carried out. In the context of an aerodrome they can be used for taxiways as well as runways. For (active) runways there are strict regulations describing when it is acceptable to issue a conditional clearance.


Conditional phrases, such as “behind landing aircraft” or “after departing aircraft”, shall not be used for movements affecting the active runway(s), except when the aircraft or vehicles concerned are seen by the appropriate controller and pilot. The aircraft or vehicle causing the condition in the clearance issued shall be the first aircraft/vehicle to pass in front of the other aircraft concerned. In all cases a conditional clearance shall be given in the following order and consist of:

a) identification;

b) the condition;

c) the clearance; and

d) brief reiteration of the condition,

for example:


Note. — This implies the need for the aircraft receiving the conditional clearance to identify the aircraft or vehicle causing the conditional clearance.

(ICAO Doc 4444 PANS ATM 12.2.7)


2.3 Regarding runways, TOC deduces that conditional clearances can realistically only be issued to enter a runway in use. Issuing a take-off or landing clearance in this manner would theoretically be possible but seems impractical and potentially very unsafe. Conditions must be such that visual observation of both receiving traffic and the traffic causing the condition must be established by the controller and that the aircraft or vehicle causing the condition must be in sight for the flight crew receiving the clearance. Perhaps significantly, it is noted explicitly that visibility must be sufficient for all parties concerned to observe and identify the traffic causing the condition. However, it is not noted that conditional clearances are not to be issued to vehicles.

2.4 Conditional clearances are mainly used to expedite the flow of traffic at a busy runway or as a tool for time management by a controller on a busy frequency. [BEHIND… BEHIND] is an additional reminder to the receiving end that they are not number 1 and must let other traffic pass before executing the clearance. It is not permitted to issue a clearance conditional on two or more traffic elements.

2.5 While the procedure for issuing conditional clearances only mentions aircraft as being the movements for which they may be issued, Doc 4444 does not explicitly forbid issuing such clearances to vehicles. It is furthermore immediately preceded by the following:

Phraseologies for the movement of vehicles, other than tow-tractors, on the manoeuvring area shall be the same as those used for the movement of aircraft, with the exception of taxi instructions, in which case the word “PROCEED” shall be substituted for the word “TAXI” when communicating with vehicles.

(ICAO Doc 4444 PANS ATM 12.2.6)


One can interpret the above as an opening to issue conditional clearances to vehicles if the phraseologies used are the same.


All vehicles and pedestrians shall give way to aircraft which are landing, taxiing or taking off, except that emergency vehicles proceeding to the assistance of an aircraft in distress shall be afforded priority over all other surface movement traffic. In the latter case, all movement of surface traffic should, to the extent practicable, be halted until it is determined that the progress of the emergency vehicles will not be impeded.



In an emergency situation, vehicles that are tasked with assisting an aircraft in distress are to be afforded the first priority in their movement through the manoeuvring area. The only exception being traffic that is currently landing or taking off. There are 2 reasons for this exception, namely: a) landings and take-offs are not considered surface movement traffic, and b) aborting a landing or take-off is an inherently dangerous proposition, especially when the aircraft are traveling at high speed.

2.7 For the purposes of this paper, emergency situations are defined as any situation in which it has been determined that immediate assistance by the fire brigade is needed upon landing of the aircraft in question, whether initiated by the pilot or ATC and whether immediate emergency or precautionary.

2.8 ICAO Doc 9870 – Manual to Prevent Runway Incursions Appendix A-4:


2.5 Conditional clearances must consist of the condition before the line-up instruction, and an acknowledgement of the correct (or otherwise) readback is required as part of the correct procedure.


2.6 The acknowledgement of a conditional clearance must contain the condition in the readback.


2.7 The procedure makes no provision for vehicles to receive a conditional clearance.

Note 1. — Conditional phrases such as “behind landing aircraft” or “after departing aircraft” shall not be used for movements affecting the active runway(s), except when the aircraft or vehicles concerned are seen by the appropriate controller and pilot.

Note 2. — The aircraft or vehicle that is the subject of a conditional clearance should be clearly identified, and the identification should always be read back in full.


The above appears in ICAO’s Manual to Prevent Runway Incursions (Doc 9870). Clause 2.7 is open for interpretation. No specific provision is made in Doc 4444, but it also does not prohibit the use of conditional clearances to vehicles. ICAO is silent on the matter.

In practice

2.9 Issuing conditional clearances to expedite the passage of emergency vehicles across the manoeuvring area to the affected aircraft might help the rescue and/or firefighting effort.

2.10 Allowing a controller to issue a conditional clearance to RFF vehicles may aid in preventing a delayed release of the runway due to frequency congestion, as the controller will be able to determine the most opportune moment to instruct the receiver(s).

2.11 On 18th December 2003, a FedEx MD-10 crash landed in Memphis, Tennessee. The subsequent rescue effort was reported to have been hampered by a delay in crossing an active runway in use for landing (NTSB/AAR-05/01, May 2005, National Transportation Safety Board). The report stated that while there were RFF vehicles already onsite, additional resources were held for two minutes before being allowed to cross an active landing runway.

2.11.1 It was stated that after landing traffic was clear of the intersection there was a further delay in issuing the clearance to cross the runway. A conditional clearance might have allowed the RFF vehicles to cross the runway as soon as they perceived traffic to be clear of conflict.

2.11.2 On page 58, the report concludes that:

“The Rural/Metro Fire Department aircraft rescue and firefighting (ARFF) response vehicles were unnecessarily delayed in providing ARFF assistance because the Memphis air traffic control tower ground controller did not give them priority over other nonemergency airport traffic; under other circumstances, this could have adversely affected ARFF efforts.”

2.11.3 The NTSB recommends the following:

“Inform all air traffic control tower controllers of the circumstances of this accident, including the need to ensure that aircraft rescue and firefighting (ARFF) vehicles are not delayed without good cause when on route to an emergency and the need to relay the number of airplane occupants to ARFF responders. (A-05-017).”

2.12 Even if paragraph 12.2.7 of Doc 4444 and Appendix A-4 of Doc 9870 are read as a general prohibition on issuing conditional clearances to vehicles, chapter 15.1 of PANS ATM states the following:

The various circumstances surrounding each emergency situation preclude the establishment of exact detailed procedures to be followed. The procedures outlined herein are intended as a general guide to air traffic services personnel. Air traffic control units shall maintain full and complete coordination, and personnel shall use their best judgement in handling emergency situations.

(ICAO Doc 4444


2.12.1 This statement exemplifies the reality experienced by controllers. Special circumstances sometimes require special measures that may not always be codified in procedure. Air traffic control units should always have full authority and the freedom to manage any emergency as they see fit. On the other hand, a clear and concise procedure that allows controllers to conditionally clear an appropriately trained RFF unit onto a runway in case of an emergency or precautionary landing would be preferable to one-off procedures improvised during an emergency.

2.13 Examples of procedures like the ones stated above are in operation at London Gatwick (“Virgin VS43 Gatwick Emergency Landing with Radio” – Posted on YouTube on 29th December 2014 – and Amsterdam Airport Schiphol, as well as in Australia. It should be noted that only approved vehicles can receive conditional clearances in these cases. While conditional clearances to RFF vehicles are not specifically codified in procedure at Schiphol, they have seen use in situations where RFF vehicles were tactically deployed at a dedicated runway for an aircraft affected by an emergency. The phraseologies used for these conditional clearances are Dutch translations of the ICAO phraseology. In the video of the incident in London Gatwick the controller and vehicles can also be heard using the standard ICAO phraseology.

Implementation and safety concerns

2.14 A consultation among tower controllers conducted by the author reveals that conditional clearances to vehicles are not widely used among tower controllers globally. This suggests that operational practice has not led to their widespread application. However, there are several instances of their usage, both officially and unofficially. It seems that, under certain circumstances, the use of conditional clearances to (RFF) vehicles has been deemed safe.

2.15 The same consultation involved multiple sources expressing their worry that such procedures could add a significant hazard during an already critical situation. A misinterpreted conditional clearance could easily cause a much more dangerous situation. It is important to note that RFF crews are inherently less familiar with the manoeuvring area and the traffic patterns near runways than pilots.

2.16 Not all aerodromes have a professional, dedicated fire brigade. It would be inadvisable to devise complex procedures at those airfields where this is the case, or to use conditional clearances at all if a certain standard of training is not met.

2.17 As it is of the utmost importance that conditional clearances are correctly understood and executed according to their intention, all parties involved must be proficient in the language used and the ICAO phraseology.


For the purposes of this paper, the conclusions below shall only apply to RFF vehicles.

3.1 ICAO does not explicitly forbid conditional clearances to RFF vehicles. Docs 4444 and 9870 imply that they are not to be issued to vehicles but leave room for interpretation.

3.2 Every second counts in emergency situations. One example has been included in which it could be argued that a conditional clearance would have expedited RFF resources reaching a crash site.

3.3 Doc 4444 gives controllers leeway to exercise their professional judgement during emergencies, thereby implying that procedures can be modified or interpreted as practicable if the controller’s best judgement is that it might increase the safety of the situation. It also states that all emergencies are different and therefore designing procedures to cover them all is impossible.

3.4 A clearly defined procedure provides guidance and security for controllers and RFF crews in non-standard situations that can prevent dangerous misunderstandings.

3.5 From the discussion above it is concluded that procedures for conditional clearances to RFF vehicles can be implemented locally under the following conditions:

– A robust investigation is conducted to construct a safety case that shows that there are no hazards introduced that cannot be sufficiently mitigated by procedures and/or training, thereby ensuring that the handling of emergencies is not inadvertently made more hazardous.

– An aerodrome where these procedures are implemented must have a dedicated RFF unit that is appropriately trained in ICAO phraseology and familiar with the aerodrome.

– Controllers are sufficiently trained to implement these procedures and are aware of the potential hazards of issuing conditional clearances.

3.6 Controllers should be free to judge the safety of each situation on its own circumstances and make decisions accordingly.


4.1 It is recommended that IFATCA policy is:

The implementation of procedures for conditional clearances to Rescue and Firefighting vehicles is only acceptable if:

– A local safety analysis is conducted. 

– The aerodrome concerned has a dedicated Rescue and Firefighting unit that is appropriately trained and familiar with the aerodrome.

– Controllers are sufficiently trained to implement said procedures and are aware of the potential hazards of issuing conditional clearances.



ICAO Doc 9870 Manual to Prevent Runway Incursions

NTSB/AAR-05/01, May 2005, National Transportation Safety Board

“FULL Virgin VS43 Gatwick Emergency Landing with Radio”- Posted on YouTube on 29th December 2014 <>

Last Update: October 1, 2020  

January 17, 2020   778   Jean-Francois Lepage    2017    

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