Simultaneous Independent Approaches
Dual and triple simultaneous independent parallel instrument approaches, are authorized at certain airports with specified distances between parallel runway centerlines. As a part of the simultaneous independent approach approval, an NTZ must be established to ensure proper flight track boundaries for all aircraft. Outside of the NTZ, normal operating zones (NOZ) indicate the operating zone within which aircraft remain during normal approach operations. The NOZ between the final approach courses varies in width depending on the runway centerline spacing. The NTZ is defined as a 2,000-foot wide area located equidistant between the final approach courses in which flight is not allowed during the simultaneous operation. [Figure 4-46] Any time an aircraft breaches or is anticipated to breach the NTZ, ATC issues instructions for the threatened aircraft on the adjacent final approach course to break off the approach to avoid potential conflict.
A local controller for each runway is also required. Dedicated final monitor controllers for each runway monitor separation, track aircraft positions and issue instructions to pilots of aircraft observed deviating from the final approach course. [Figure 4-45] These operations are normally authorized for ILS, LDA and RNAV approach procedures with vertical guidance. For simultaneous parallel ILS approach operations, pilots should review the chart notes to determine whether the non-precision LOC procedure is authorized (in the event of glide slope equipment failure either in the aircraft or the ground). An example of a restriction on the use of a LOC procedure is shown in the notes on Figure 4-24: “LOC procedure NA during simultaneous operations”. Likewise, for RNAV (GPS) approaches, use of LNAV procedures are often restricted during simultaneous operations.
Triple simultaneous independent approaches are authorized provided the runway centerlines are separated by at least 3900 feet for triple straight in approaches. If one or both outside runways have an offset approach course of 2.5° to 3.0°, the spacing between those outer runways and the center runway may be reduced to 3000 feet.
Simultaneous Close Parallel Precision Runway Monitor (PRM) Approaches
Simultaneous close parallel (independent) PRM approaches are authorized for use at designated airports that have parallel runways spaced less than 4,300 feet apart. [Figure 4-47] Certain PRM approaches are referred to as Simultaneous Offset Instrument Approaches (SOIA) and are discussed in depth later in this category.
PRM procedures are the most efficient method of increasing approach capacity at airports with closely spaced, parallel runways. Use of PRM procedures increases airport capacity during periods of low visibility by providing ATC the capability to monitor simultaneous close parallel (independent) approaches. These PRM operations reduce delays and increase fuel savings. Traditionally the PRM system included a high-update rate radar, a high resolution ATC radar display, as well as software that can autonomously track aircraft in close to real time, with visual and aural alerts that depict the aircraft’s current position and velocity as well as displaying a ten-second projected position to the controllers. Today, most PRM operations are conducted without the need for high update rate radar, so long as all of the other requirements to conduct such approaches are met.
There are also special communications and ATC requirements for PRM approaches. PRM approaches require a final NTZ monitor controller for each runway, a separate tower controller for each runway, a PRM tower frequency, and a runway-specific PRM frequency. Each final monitor controller will have a dedicated PRM frequency, and the tower controller will have a separate common PRM frequency. Pilots transmit and receive on the common tower PRM frequency, but maintain listening watch on the final controller’s PRM frequency for their specified runway. The final monitor controller has override capability on their PRM frequency. In that way, if the common tower frequency is blocked, the monitor controller’s instructions will be heard by the pilot on the monitor controller’s PRM frequency. Pilot training is prescribed and required for pilots prior to using the PRM procedures. The FAA PRM website (http://www.faa.gov/training_testing/ training/ prm/) contains training information for PRM approaches and hosts PRM training materials for download or viewing online.”
When pilots or flight crews wish to decline a PRM approach, ATC must be notified immediately and the flight will be transitioned into the area at the convenience of ATC. Pilots who are unable to accept a PRM approach may be subject to delays.
The approach chart for the PRM approach requires review of the accompanying AAUP page, which outlines pilot, aircraft, and procedure requirements necessary to participate in PRM operations. [Figure 4-48] Pilots need to be aware of the differences associated with this type of approach. Differences, as compared to other simultaneous approaches, are listed below:
- Immediately follow break out instructions as soon as safety permits.
- Use of the AAUP.
- Use of dual VHF communications.
- Completion of required PRM training.
- Handflying any breakout instruction. It is important to note that descending breakouts, though rare, may be issued. Flight crews will never be issued breakout instructions that clear them to an altitude below the MVA, and they are not required to descend at more than 1,000 fpm.
- Traffic Alert and Collision Avoidance System (TCAS) is not required to conduct a PRM approach. For aircraft so equipped, if the controller’s climb/descendinstruction differs from the TCAS resolution advisory (RA), pilots must follow the RA while continuing tofollow the controller’s turn instruction. Report thisdeviation to ATC as soon as practical.
Simultaneous Offset Instrument Approaches (SOIAs)
SOIAs allow simultaneous approaches to two parallel runways spaced at least 750 feet apart, but less than 3,000 feet. Traditionally, the SOIA procedure has used an ILS/ PRM approach to one runway and an offset localizer-type directional aid (LDA)/PRM approach with glideslope to the adjacent runway. Now, RNAV (GPS) and RNAV (RNP) approaches may also be used for SOIA.” Approach charts will include procedural notes, such as “Simultaneous Close Parallel approach authorized with LDA PRM RWY 28R and RNAV (GPS) PRM X RWY 28R.” or “Simultaneous approach authorized”. San Francisco had the first published SOIA approach. [Figure 4-49]
The training, procedures, and system requirements for SOIA ILS/PRM and LDA/PRM approaches are identical with those used for simultaneous close parallel ILS/PRM approaches until near the LDA/PRM approach MAP, where visual acquisition of the ILS aircraft by the LDA aircraft must be accomplished. If visual acquisition is not accomplished prior to reaching the LDA MAP , a missed approach must be executed. A visual segment for the LDA/PRM approach is established between the LDA MAP and the runway threshold. Aircraft transition in visual conditions from the LDA course, beginning at the LDA MAP, to align with the runway and can be stabilized by 500 feet AGL on the extended runway centerline. Pilots are reminded that they are responsible for collision avoidance and wake turbulence mitigation between the LDA MAP and the runway.
The FAA website has additional information about PRM and SOIA approaches, including an instructional PowerPoint training presentation at http://www.faa.gov/training_testing/training/prm/.