Two closing subjects share this lesson. The first is geometric: how the world's busiest airports run instrument approaches and departures to two parallel runways at once without the streams ever touching — a system of zones, radar standards and diverging tracks. The second is legal: Regulation (EU) No 965/2012, the Air Operations Regulation, the rulebook under which every European operator actually flies, and the map of its annexes that the exam expects a pilot to navigate.
Approaching parallel runways
When both parallel runways serve arrivals at the same time, the first question is whether the two streams are separated from each other:
Independent parallel approaches — radar separation minima between aircraft on adjacent extended runway centre lines are not prescribed: each stream flies as if alone, and the geometry of the system does the separating.
Dependent parallel approaches — radar separation minima between aircraft on the adjacent centre lines are prescribed: the two streams are staggered diagonally against each other, each aircraft separated from its neighbour on the other approach.
Independent operations move more traffic; they also demand more from the equipment, the airspace and the monitoring.
The full menu of simultaneous operations has four further entries, and the exam asks for all of them:
Simultaneous instrument departures — both parallel runways used for departures at the same time, the nominal departure tracks diverging by at least 15 degrees immediately after take-off so the streams open apart from the first second of flight.
Segregated parallel operations — one runway used exclusively for approaches while the other is used exclusively for departures: arrivals and departures never share a runway.
Semi-mixed operations — one runway used exclusively for one kind of operation while the other handles both: for example, one runway departures only, the other runway arrivals and departures.
Mixed operations — both runways handle both arrivals and departures: the most flexible mode and the most demanding to manage.
NOZ and NTZ: the geometry of independence
Independent parallel approaches work because the airspace between the two localizer courses (the final approach guidance beams) is policed:
Normal operating zone (NOZ) — airspace of defined dimensions extending either side of each final approach track, within which an aircraft flying its approach normally is expected to remain.
No transgression zone (NTZ) — a corridor of defined dimensions between the two NOZs, centrally between the extended runway centre lines, the penetration of which by an aircraft requires the controller to intervene, manoeuvring the threatened aircraft on the adjacent approach.
An aircraft may wander within its NOZ without consequence; the instant it breaks into the NTZ, the monitoring controller turns the aircraft on the other approach away. The figure draws the corridor.