Parallel or Near-parallel Runway Operation — Page 240, Lesson 316

Let’s pick up with the missed approach procedure for simultaneous parallel operations, because that’s where the rules get really specific. 12.14 Missed Approach. When you’re doing simultaneous parallel operations and you have to go around, the missed approach track and the departure tracks must diverge by a minimum of 30 degrees. That’s a hard number — 30 degrees of divergence. If the procedure prescribes turns to establish that divergence, you as the pilot are to commence those turns as soon as practicable. Not when it’s convenient, not when you’re comfortable — as soon as practicable. The whole point is to keep you away from the traffic on the adjacent runway as quickly as possible. Now let’s move to Runway Spacing, which is 12.15. 12.15 Minimum Spacing of Parallel Runways. Here’s the worst case: the runway thresholds — or the normal rotation points — are adjacent. What does that mean? It means two approaching aircraft will always be at the same altitude when they’re at the same distance from touchdown. They’re side by side, same distance out, same height — no natural vertical separation. That’s the dangerous scenario. But if the thresholds are staggered — offset from each other along the runway direction — then you introduce a degree of vertical separation. Same for departing aircraft. Because one runway’s threshold is further down, an aircraft on one approach is at a different height than the one on the other at the same point. That staggered arrangement permits closer spacing of the runways. And here’s the exact trade: you get a 30 metre reduction or increment for every 150 metres of overlap. So for every 150 metres the thresholds overlap, you can bring the runways 30 metres closer together. That’s the case at Manchester, for example. Now, the minimum spacing values you must know cold: - Mode 1 operations: 1035 metres - Mode 2 operations: 915 metres - Modes 3 and 4 operations: 760 metres So Mode 1 is the widest spacing, Mode 2 is tighter, and Modes 3 and 4 are the tightest at 760 metres. The diagrams in the figures show the requirements for spacing of parallel runways — and illustrate this. Finally, 12.16 Wake Turbulence Considerations. The full implications of wake turbulence are covered in other subjects, and later in these notes under ATC we’ll discuss wake turbulence separation. But here’s the key point for parallel runways: using parallel runways introduces problems with wake turbulence from aircraft on adjacent runways. This is a major limitation to the flexibility that parallel runway operations facilitate. Here’s the rule: if the spacing between runways is less than 760 metres, OR if the flight paths of departing or arriving traffic cross at the same altitude — or within 1000 feet below the higher level — then wake turbulence separation must be applied. So that 760 metre figure comes back. Below that spacing, you can’t just assume you’re clear — you need wake turbulence separation. And even if the runways are spaced wider, if the flight paths cross at the same altitude, or within 1000 feet below the higher aircraft, you still need that separation. That’s the limitation that reduces the flexibility of parallel operations. So to tie it together: 30 degrees of divergence on missed approach, 1035/915/760 metre minimums for the four modes, the 30 metre per 150 metre stagger trade, and the 760 metre / 1000 feet wake turbulence trigger. That’s the core of parallel runway spacing.