Parallel or Near-parallel Runway Operation — Page 240, Lesson 311

All right, let's get into the heart of parallel runway operations. We've covered the basic concept, and now we're moving through the specific modes. We're starting with Mode 2, which is Dependent Parallel Approaches. Here's the core idea: we have two parallel runways, and aircraft are making approaches to both of them simultaneously. The key word here is dependent. This means the aircraft on one approach are not completely independent of the aircraft on the other. They are separated by a specific radar minimum, and that separation is actively managed by air traffic control. So, the definition is: approaches are made to parallel runways where radar separation minima between aircraft using adjacent ILS and/or MLS are applied. Let's unpack that. ILS is the Instrument Landing System, and MLS is the Microwave Landing System. These are the precision approach aids that guide the aircraft down to the runway. The separation between aircraft on these adjacent approaches is a radar separation minimum, meaning the controllers use radar to ensure the aircraft stay a specific distance apart. Now, the rules for this mode are very strict. Regardless of the weather conditions, all approaches are to be radar monitored. This isn't optional; it's mandatory. And the radar controllers doing this monitoring are specifically detailed for that duty only. They have one job, and one job only: watching those approaches. To do this effectively, they are given dedicated discrete RTF frequencies. RTF is the Radio Telephony frequency, so each of these dedicated controllers has their own private radio channel to talk to the aircraft they're monitoring. The procedures are also tightly controlled. Only straight-in approaches are permitted. That means the aircraft must be lined up with the runway heading and come straight in. Track reversal procedures are not permitted. A track reversal is a maneuver like a procedure turn, where the aircraft flies away from the runway and then turns back to intercept the final approach course. That's a no-go in this mode. Now, let's look at the vectoring rules. When the controller is vectoring an aircraft to intercept the localizer, there are specific limits. The maximum interception angle permitted is 30°. So the aircraft can't be steered at a steeper angle to catch the localizer. Also, a minimum of 1 NM straight and level flight is required before localizer intercept. The aircraft must be flying straight and level for at least one nautical mile before it actually crosses the localizer. This ensures a stable setup. And there's more. The vectoring is also to ensure that the localizer track is intercepted and flown for at least 2 NM before glide path intercept. So once the aircraft is on the localizer, it must fly that localizer for at least two nautical miles before it's allowed to start descending on the glide path. This is all about building in stability and predictability. Until the aircraft is established on the localizer, the normal minimum radar separation of 5 NM shall apply. So, before that point, the aircraft are treated like any other radar targets and must be kept 5 nautical miles apart. Once they're on the localizer, the reduced separation minima for the parallel approach can be applied. Finally, there's a critical equipment requirement. Aircraft carrying out parallel operations must be equipped with full ILS/MLS. This is a hard requirement. If the aircraft doesn't have the full capability, it cannot participate in this operation. Let's move on to Mode 3, which is Simultaneous Instrument Departures. This operation is also known as Mode 3 Independent Parallel Departures. The name tells you a lot. It involves simultaneous departures for aircraft departing in the same direction from parallel runways. Two aircraft, on two parallel runways, taking off at the same time, heading the same way. There are two key conditions here. First, all departing traffic must be identified by radar at a distance of not more than 1 NM from DER. DER is the Departure End of Runway. So, within one nautical mile of the end of the runway, the radar controller must have positively identified the aircraft. Second, all departure tracks must diverge by a minimum of 15° immediately after take-off. The aircraft must turn away from each other, with their tracks separating by at least 15 degrees, right after they lift off. There's also an important note here about wake turbulence. When the minimum distance between two parallel runways is less than the specified value for wake turbulence separation considerations for departing aircraft, the runways are considered to be a single runway. In that case, a simultaneous dependent parallel departure mode is not used. So, if the runways are too close together, the wake turbulence from one departing aircraft could affect the other, so they can't be treated as independent. They're treated as one runway, and the operation changes. Now, let's look at Mode 4, which is Segregated Departures/Arrivals. This operation is known as Mode 4 Segregated Parallel Operations. The concept here is simple and elegant. In this mode, one runway is used exclusively for approaches, and the other runway is used exclusively for departures. So, you have a dedicated arrival runway and a dedicated departure runway. This is the mode of operation at London Heathrow. It's a very efficient way to handle a high volume of traffic, because the arrival flow and the departure flow don't interfere with each other on the same runway. So, to summarize the three modes we've covered: Mode 2 is dependent approaches, where aircraft are separated by radar on adjacent ILS/MLS approaches. Mode 3 is independent departures, where aircraft take off simultaneously and must diverge immediately. And Mode 4 is segregated operations, where one runway is for arrivals and the other is for departures. Each mode has its own specific rules and requirements, and it's crucial to understand which mode is in use and what the applicable procedures are.