Airports that have two or three parallel runways may be authorized to use parallel approaches to maximize the capacity of the airport. There are three classifications of parallel ILS approaches, depending on the runway centerline separation and ATC procedures.


Parallel (dependent) ILS approaches are allowed at airports with parallel runways that have centerlines

Figure 5-39. Category III Approach Procedure.

separated by at least 2,500 feet. Aircraft are allowed to fly ILS approaches to parallel runways; however, the aircraft must be staggered by a minimum of 1 1/2 NM diagonally. Aircraft are staggered by 2 NM diagonally for runway centerlines that are separated by more than 4,300 feet and up to but not including 9,000 feet, and that do not have final monitor air traffic controllers. Separation for this type of approach is provided by radar. [Figure 5-40]

Figure 5-40. Parallel (Dependent) ILS Approach Separation Criteria.

Though this type of approach procedure is approved for several airports, it is not required that the approach chart contain information notifying flight crews of the use of parallel approaches. Therefore, a pilot may not know that parallel approaches are approved or used at a specific airport based on the information contained on the chart. ATC normally communicates an advisory over ATIS that parallel approach procedures are in effect. For example, pilots flying into Sacramento, California may encounter parallel approach procedures. [Figure 5-41]

Figure 5-41. Sacramento International (KSMF), Sacramento, California, ILS RWY 16L.


Simultaneous parallel ILS approaches are used at authorized airports that have between 4,300 feet and 9,000 feet separation between runway centerlines. A dedicated final monitor controller is required to monitor separation for this type of approach, which

Figure 5-42. Charlotte/Douglas International (KCLT),
Charlotte, North Carolina, ILS RWY 18.

eliminates the need for staggered approaches. Final monitor controllers track aircraft positions and issue instructions to pilots of aircraft observed deviating from the LOC course. [Figure 5-42]

Triple simultaneous approaches are authorized provided the runway centerlines are separated by at least 5,000 feet and are below 1,000 feet MSL airport elevation. Additionally, for triple parallel approaches above airport elevations of 1,000 feet MSL, ASR with high-resolution final monitor aids or high update RADAR with associated final monitor aids is required.

As a part of the simultaneous parallel approach approval, normal operating zones and non-transgression zones must be established to ensure proper flight track boundaries for all aircraft. The normal operating zone (NOZ) is the operating zone within which aircraft remain during normal approach operations. The NOZ is typically no less than 1,400 feet wide, with 700 feet of space on either side of the runway centerline. A no transgression zone (NTZ) is a 2,000-foot wide area located between the parallel runway final approach courses. It is equidistant between the runways and indicates an area within which flight is not authorized. [Figure 5-43 on page 5-54] Any time an aircraft breaches the NTZ, ATC issues instructions for all aircraft to break off the approach to avoid potential conflict.