When parallel runway centrelines are separated by more than 9000'/2745 m (9200' if airport elevation is above 5000' MSL), no specific restrictions are imposed on simultaneous approach procedures once the aircraft is established on the final approach course. However, when centrelines are spaced by 9000' or less, special procedures must be put in force to help preclude Loss of Separation between aircraft conducting simultaneous approaches.
ATC procedures permit ILS/RNAV/GLS instrument approach operations to dual or triple parallel runway configurations. ILS/RNAV/GLS approaches to parallel runways are categorised as either Dependent approaches or Independent approaches. Simultaneous approaches to parallel runways with centerline spacing of 9000' or less fall into one of the following three classes:
- Simultaneous Parallel Dependent Approaches
- Simultaneous (Parallel) Independent Approaches
- Simultaneous Close Parallel PRM Approaches (Independent)
RNAV approach procedures that are approved for simultaneous operations require GPS as the sensor for position updating. VOR/DME, DME/DME and IRU RNAV updating is not authorized.
Pilots will be advised that simultaneous dependent approaches, simultaneous approaches, or simultaneous close parallel PRM approaches are in use. This information may be provided through the ATIS.
Parallel approach operations require heightened pilot situational awareness. A thorough review of the Approach Chart should be conducted with emphasis on the following approach information:
- name and number of the approach
- location and proximity of the assigned runway relative to adjacent parallel runway(s)
- localizer frequency
- inbound course
- glide slope intercept altitude
- glideslope check altitude
- decision height
- missed approach procedure
- special notes or procedures
The close proximity of aircraft conducting approaches to adjacent runways demands strict and timely compliance with ATC assigned speeds, altitudes and headings. Precise final approach course tracking is critical to maintaining required separation. Pilots should notify ATC immediately in the event of loss or degradation of aircraft or navigation systems.
Strict radio discipline is mandatory during simultaneous parallel approach operations. Lengthy or unnecessary radio transmissions must be avoided. Full and proper call signs should be used to prevent the inadvertent execution of clearances intended for another aircraft or confusion due to similar sounding call signs. Pilots must be alert to unusually long periods of silence or any unusual background sounds in their radio receiver as a stuck microphone could block the issuance of ATC instructions.
Traffic Collision Avoidance Systems (TCAS) provide an additional element of safety to parallel approach operations. Pilots should follow recommended TCAS operating procedures in the event of a Resolution Advisory (RA).
Description of Parallel Approaches
The three classes of parallel approaches are depicted in the diagram below with more detailed descriptions following.
Parallel Approaches (Source: FAA AIM)
Simultaneous Parallel Dependent Approach
Simultaneous parallel dependent approaches are an ATC procedure permitting approaches to airports having parallel runway centerlines separated by between 2,500 feet and 9,000 feet. Separation between aircraft is achieved by "staggering" the aircraft, as depicted in the diagram below, at a specified minimum diagonal distance corresponding to the runway centreline separation.
Diagonal Separation (Source: FAA AIM)
Simultaneous (Parallel) Independent Approaches
Simultaneous Independent Approach is a system permitting simultaneous ILS/RNAV/GLS approaches to parallel runways with centerlines separated by 4,300 to 9,000 feet utilising No Transgression Zone (NTZ) final monitor controllers. Simultaneous independent approaches require NTZ radar monitoring to ensure that separation between aircraft on the adjacent parallel approach course is maintained. Staggered radar separation procedures are not utilised. Aircraft position is tracked by final monitor controllers who will issue instructions to aircraft observed deviating from the assigned final approach course.
As is the case for parallel runways separated by more than 9000', aircraft turning onto final approach will be provided 3 miles radar separation or a minimum of 1,000 feet vertical separation from aircraft joining the approach for the other runway. The assigned altitude must be maintained until intercepting the glide path, unless otherwise cleared by ATC. Aircraft will not be vectored to intercept the final approach course at an angle greater than thirty degrees.
The final NTZ monitor controller has the capability of overriding the tower controller on the tower frequency. Pilots will be instructed to contact the tower frequency prior to the point where NTZ monitoring begins. Aircraft observed to overshoot the turn−on or to continue on a track which will penetrate the NTZ will be instructed to return to the correct final approach course immediately. If required, the final monitor controller may cancel the approach clearance, and issue missed approach or other instructions to the deviating aircraft. If the deviating aircraft fails to respond to such instructions or is observed penetrating the NTZ, the aircraft on the adjacent final approach course (if threatened), will be issued a breakout instruction. Radar monitoring will automatically be terminated when visual separation is applied, the aircraft reports the approach lights or runway in sight, or the aircraft is 1 mile or less from the runway threshold. Final monitor controllers will not advise pilots when radar monitoring is terminated.
The above procedures are depicted in the following diagram:
Simultaneous (Parallel) Independent Approaches (Source: FAA AIM)
Simultaneous Close Parallel PRM Approaches
Simultaneous Close Parallel PRM Approach is a system allowing independent ILS to runways with centre line spacing of less than 4300' but not less than 3000'. Simultaneous Offset Instrument Approach (SOIA) is a procedure used to conduct simultaneous approaches to runways spaced less than 3,000 feet, but at least 750 feet apart. PRM is an acronym for the high update rate Precision Runway Monitor surveillance system which is required to monitor the No Transgression Zone (NTZ) and is necessary to conduct simultaneous close parallel approaches. PRM is also published in the title as part of the approach name for the Instrument Approach Procedure used to conduct Simultaneous Close Parallel approaches. “PRM” alerts pilots that specific airborne equipment, training, and procedures are applicable. Because of their complexity, Simultaneous Close Parallel PRM Approach and SOIA are covered more fully in dedicated articles. Some of the basic Simultaneous Close Parallel PRM Approach criteria are detailed in the following diagram.
Simultaneous Close Parallel PRM Approach (Source: FAA AIM)
Accidents and Incidents
The following runway excursion events involved parallel approach operations:
On 13 November 2012, a Garuda Airbus A330 and a KLM Boeing 737 lost separation against each other whilst correctly following radar vectors to parallel approaches at Amsterdam but there was no actual risk of collision as each aircraft had the other in sight and no TCAS RA occurred. The Investigation found that one of the controllers involved had used permitted discretion to override normal procedures during a short period of quiet traffic but had failed to restore normal procedures when it became necessary to do so, thus creating the conflict and the ANSP was recommended to review their procedures.
On 27 May 2018, four losses of separation on final approach during use of dependent parallel landing runways occurred within 30 minutes at Madrid following a non-scheduled weather-induced runway configuration change. This continuing situation was then resolved by reverting to a single landing runway. The Investigation attributed these events to “the complex operational situation” which had prevailed following a delayed decision to change runway configuration after seven consecutive go-arounds in 10 minutes using the previous standard runway configuration. The absence of sufficient present weather information for the wider Madrid area to adequately inform ATC tactical strategy was assessed as contributory.
On 16 May 2018, an Airbus A310 and a Cessna 421 being positioned for ILS approaches to adjacent parallel runways at Montréal by different controllers lost separation. One controller incorrectly believed that he had transferred control of the Cessna to the other when the shift supervisor re-opened a sector which had been temporarily combined with his. The Investigation attributed the conflict to multiple deviations from standard procedures, memory lapses relating to controller information exchange of information and a loss of full situational awareness compounded by the shift supervisor also acting as an instructor whilst being distracted by his other duties.
Some airports operating parallel runways
The following map shows some of the aerodromes operating parallel runways which are listed on SKYbrary: