This lesson is about the tower's half of the conversation: the fixed lists of information every aircraft is owed at each stage of arrival and departure, the priority rule between a landing aircraft and a waiting departure, the five-minute clock on an arrival that goes quiet, and the procedures the tower runs when VFR operations are suspended. In the middle sits the syllabus's second visit to parallel runways: the operating combinations and the prerequisites that make simultaneous operations legal.
What the arriving aircraft is told
As early as practicable after an aircraft intending an approach for landing establishes communication with approach control, it receives, in order, everything it needs to plan the arrival, except any element it is known to have already (the ATIS exists to absorb most of this list):
The type of approach and the runway-in-use.
The meteorological information — surface wind direction and speed, including significant variations; visibility and, when applicable, RVR; present weather; cloud below 1,500 m (5,000 ft) or below the highest minimum sector altitude, whichever is greater, plus any cumulonimbus, and, when available, the vertical visibility if the sky is obscured; air temperature; dew point (where regionally agreed); altimeter settings; significant phenomena in the approach area; and the trend-type landing forecast when available.
Current runway surface conditions when there are precipitants or other temporary hazards — precipitants meaning deposits on the surface: water, snow, slush and their relatives.
Changes in the operational status of visual and non-visual aids essential for approach and landing.
If it later becomes necessary or desirable that the aircraft use a different procedure or runway than initially stated, the crew is advised without delay. Then the funnel narrows, and the lists narrow with it. At the commencement of final approach, the aircraft receives: significant changes in the mean surface wind (when the controller holds component data, significant means a mean headwind change of 10 kt, tailwind 2 kt, crosswind 5 kt); the latest information on wind shear or turbulence in the final approach area; and the current visibility or RVR with its trend. During final approach, only what cannot wait is transmitted, and it goes without delay: the sudden occurrence of hazards (unauthorised traffic on the runway is the document's own example), significant variations in the surface wind given as minimum and maximum values, significant changes in the runway surface conditions, changes in the status of required aids, and changes in RVR or visibility.
What the departing aircraft is told
The tower's own lists mirror the arrival's, keyed to the three moments the syllabus names. Prior to taxiing for take-off, in order, minus anything already received:
The runway to be used.
The surface wind direction and speed, with significant variations.
The QNH — and, by local arrangement or on request, the QFE.
The air temperature for the runway, for turbine-engined aircraft — the number their take-off performance is computed from.
The visibility representative of the take-off and initial climb direction if less than 10 km, or the RVR.
The correct time.
Prior to take-off, the aircraft is advised of any significant changes in the surface wind, air temperature and visibility or RVR since the taxi information, and of significant meteorological conditions in the take-off and climb-out area. The document's own list of what counts: cumulonimbus or thunderstorm, moderate or severe turbulence, wind shear, hail, moderate or severe icing, severe squall line, freezing precipitation, severe mountain waves, sandstorm, duststorm, blowing snow, tornado or waterspout, occurring or expected. And the duty does not end at the runway: once the departing aircraft has established communication with the approach control unit, significant changes obtained there (in that same phenomenon list, or in the surface wind, visibility, RVR or air temperature) are transmitted to it without delay, except when the aircraft is known to have the information already. Prior to entering the traffic circuit or commencing the approach, the short list returns: the runway to be used, the surface wind with significant variations, and the QNH (QFE by arrangement or on request).
Priority, and the arrival that goes quiet
Between the runway's two customers the rule is one sentence: an aircraft landing, or in the final stages of an approach to land, shall normally have priority over an aircraft intending to depart from the same or an intersecting runway: the aircraft with energy and momentum committed wins over the one still standing still. And the tower is also the system's last tripwire for a vanished arrival: an aircraft that fails to report after being transferred to the tower, or reports once and then ceases radio contact, and in either case fails to land within five minutes of the expected landing time, is reported to the approach control unit, ACC or flight information centre (or to the rescue coordination centre or sub-centre) in accordance with local instructions. Those five minutes are the same trigger the alerting lesson met from the other side: the ALERFA that a cleared-to-land aircraft's silence raises.
Parallel and near-parallel runways
The combinations first; the exam asks for them by name. For departures, parallel runways may be operated with:
Independent departures — both runways used exclusively for departures.
Semi-mixed operation — one for departures and the other for a mixture of arrivals and departures.
Mixed operation — both used for mixed arrivals and departures.
For arrivals, simultaneous instrument operations come in three modes:
Independent parallel approaches — no radar separation minimum is prescribed between aircraft on the adjacent final approach tracks.
Dependent parallel approaches — a diagonal minimum still is prescribed.
Segregated parallel operations — one runway arrives while the other departs.
Whenever parallel approaches run, separate controllers should sequence and space the arrivals to each runway.
The prerequisites are what make each mode lawful, and the numbers are examinable:
Independent parallel departures — centre lines at least 760 m (2,500 ft) apart; nominal departure tracks diverging by at least 15 degrees immediately after take-off (10 degrees when both aircraft fly RNAV or RNP departures turning within 3.7 km/2.0 NM of the runway end); a surveillance system able to identify the aircraft within 1.9 km (1.0 NM) of the runway end; and procedures ensuring the divergence is achieved.
Independent parallel approaches — centre-line spacing per the prescribed table, from 1,035 m (3,400 ft) upward, with correspondingly tighter surveillance the closer the runways: below 1,310 m the system needs the highest prescribed accuracy, an update period of 2.5 seconds or less and a high-resolution display with position prediction and deviation alert. The no-transgression zone and its dedicated monitoring controllers were taught with the parallel-approach radar procedures of the altimetry-and-transponders module.
Dependent parallel approaches — centre lines 915 m (3,000 ft) or more apart; 300 m (1,000 ft) vertical or 5.6 km (3.0 NM) horizontal separation until established; 3.0 NM (or 2.5 NM where prescribed) between aircraft on the same final approach track; and diagonally between successive aircraft on the adjacent tracks, 2.0 NM for track spacings above 2,529 m, 1.5 NM above 1,097 m, and 1.0 NM above 915 m.
Segregated parallel operations — centre lines at least 760 m (2,500 ft) apart, and the nominal departure track diverging immediately after take-off by at least 30 degrees from the missed approach track of the adjacent approach. The 760 m may shrink by 30 m for each 150 m the arrival runway is staggered toward the arriving aircraft (to a floor of 300 m), and should grow by the same rate when staggered away.