12 Parallel or Near-parallel Runway Operation
12.8 Semi-mixed Operations. In essence, the option for the use of parallel runways is totally flexible and a situation may exist where one runway is used exclusively for departures, while the other runway accepts a mixture of departures and approaches, or vice versa. There may also be simultaneous parallel approaches with departures interspersed on both runways. In effect, semi-mixed operations may be permutations of the four basic modes (above). Most North American major aerodromes operate some kind of semi-mixed operations.
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Safety |
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12.9 Aircraft equipment. All aircraft carrying out parallel runway operations must be |
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equipped with full ILS/MLS |
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12.10 Radar Monitoring. For all parallel runway operations, radar surveillance (or in some |
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cases, control) must be provided regardless of the weather conditions. Without radar, parallel |
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runway operations are suspended and single runway operations resumed. |
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12.11 Approach Operations. Due to the real estate limitations of aerodromes, it is inevitable |
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that the spacing between parallel runways will not be sufficient to permit normal ATC |
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separation standards to be applied. However, whatever is implemented must be safe and |
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provide separation immediately something goes wrong. Normally, ATC separation is provided |
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either vertically or horizontally and is usually based on the accuracy of navigation of the |
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or Parallel |
aircraft. If the accuracy of navigation can be improved then the separation standard can be |
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reduced, in other words, separation can be traded off against accuracy of navigation. For |
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parallel approach operations, vertical and horizontal separation standards are overruled once |
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-Near |
the aircraft concerned are established on the localizer centre line. Mode 1 is described as |
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independent and implies that what happens on one runway is totally independent of what is |
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parallel |
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happening on the other. Mode 2 (dependent) does roughly the same but with the addition |
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Runway |
of radar separation longitudinally and laterally of approaching aircraft, making what happens |
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on one runway dependent upon what is happening on the other. Effectively for both modes, |
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Operation |
there are two arrival aerodromes albeit very close together. |
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12.12 Normal Operating Zone (NOZ). This is applicable to Mode 1 operations and is airspace |
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of defined dimensions extending either side of an ILS localizer course (or an MLS final approach |
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track centre line) within which an aircraft operating normally on the ILS would be positioned. |
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Remember - the protected zone is encompassed by half scale deviation of the CDI and is the |
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required accuracy of ILS navigation. Only the inner half of the NOZ is taken into account in |
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independent parallel approaches. |
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12.13 No Transgression Zone (NTZ). In the context of Mode 1 independent parallel |
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approaches, this is a corridor of airspace of defined dimensions located centrally between the |
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two extended runway centre lines. Penetration of the NTZ by an aircraft requires controller |
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intervention immediately to manoeuvre a threatened aircraft on the adjacent approach, out |
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of the way. Normally this would require a turn away from the other aircraft and an immediate |
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climb to MSA (or as per the Missed Approach Procedure). Once the threatened aircraft is safe, |
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the controller will attempt to assist the other aircraft regain the approach or carry out the |
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missed approach procedure. It is a requirement that the NTZ must be at least 610 m wide. |
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Parallel or Near-parallel Runway Operation 12
Figure 12.5 No transgression zone
12.14 Missed Approach. Simultaneous parallel operations require the missed approach track and departure tracks to diverge by a minimum of 30°. When turns are prescribed to establish divergence, pilots are to commence turns as soon as practicable.
Runway Spacing
12.15 Minimum Spacing of Parallel Runways. The worst case is where the runway thresholds (or the normal rotation points) are adjacent. This means that two approaching aircraft for instance, will always be at the same altitude when at the same distance from touchdown. If, however, the thresholds are ‘staggered’ then a degree of vertical separation is introduced (likewise for departing aircraft). This situation permits closer spacing of runways (30 m reduction or increment for every 150 m of overlap) as is the case for the runway at Manchester. The diagram below illustrates the requirements for spacing of parallel runways. The student should know that the minimum spacing for Mode 1 operations is 1035 m, for Mode 2 it is 915 m and for Modes 3 and 4 it is 760 m.
Parallel or Near-parallel Runway Operation 12
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12 Parallel or Near-parallel Runway Operation
Operation Runway parallel-Near or Parallel 12
Figure 12.6
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Parallel or Near-parallel Runway Operation 12
Figure 12.7
12.16 Wake Turbulence Considerations. The full implications of wake turbulence are covered in other subjects and later in these notes under the umbrella of ATC we will discuss wake turbulence separation. However, the use of parallel runways introduces problems concerning wake turbulence from aircraft using adjacent runways and this is a major limitation to the flexibility that parallel runway ops facilitate. Effectively, if the spacing between runways is less than 760 m or the flight paths of departing or arriving traffic cross at the same altitude (or within 1000 ft below the higher level) then wake turbulence separation must be applied.
Parallel or Near-parallel Runway Operation 12
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