24. A) Alerting service provided by aerodrome control Towers.

Aerodrome control towers are responsible for alerting the rescue and fire fighting services whenever:

1. an aircraft accident has occurred on or in the vicinity of the aerodrome; or,

1. information is received that the safety of an aircraft which is or will come under the jurisdiction of the aerodrome control tower may have or has been impaired; or

1. requested by the flight crew; or

1. when otherwise deemed necessary or desirable.

Procedures concerning the alerting of the rescue and fire fighting services shall be contained in local instructions. Such instructions shall specify the type of information to be provided to the rescue and fire fighting services, including type of aircraft and type of emergency and, when available, number of persons on board, and any dangerous goods carried on the aircraft.

Aircraft which fail to report after having been transferred to an aerodrome control tower, or, having once reported, cease radio contact and in either case fail to land five minutes after the expected landing time, shall be reported to the approach control unit, ACC or flight information centre, or to the rescue coordination centre or rescue sub-centre, in accordance with local instructions.

b) Navigational aids (NDB, VOR, DME, GPS)

ADF (Automatic Direction Finding): ADF is a fairly old system of radio navigation, but it is still in use today. A Non-Directional Beacon (NDB) emits a radio signal and the pilot’s cockpit display will show the direction of the beacon from the aircraft.

VOR (Very High Frequency Omni-directional Range): this is a more developed system and is currently the primary air navigation system in countries where sufficient infrastructure is in place. A VOR station can determine and transmit to the pilot the exact direction that will take the pilot over the point where the VOR station is. Many VOR stations also have Distance Measuring Equipment (DME) which informs the pilot of his / her distance from the VOR station.

GPS (Global Positioning System): many cars are now fitted with a GPS system so that you can drive without consulting a map. Pilots are also now making use of GPS satellite navigation. Originally very expensive, GPS equipment is now cheaper to buy and so even if a light aircraft is not fitted with a GPS cockpit system, many pilots will use a hand-held device.

25. A) Information for arriving aircraft.

As early as practicable after an aircraft has established communication with the unit providing approach control service, the following elements of information, in the order listed, shall be transmitted to the aircraft, with the exception of such elements which it is known the aircraft has already received:

1. type of approach and runway-in-use;

2. meteorological information, as follows:

   1. surface wind direction and speed, including significant variations;

   2. visibility and, when applicable, runway visual range (RVR);

   3. present weather;

   4. cloud below 1 500 m (5 000 ft) or below the highest minimum sector altitude, whichever is greater; cumulonimbus; if the sky is obscured, vertical visibility when available;

   5. air temperature;

   6. dew point temperature, inclusion determined on the basis of a regional air navigation agreement;

   7. altimeter setting(s);

   8. any available information on significant meteorological phenomena in the approach area; and

   9. trend-type landing forecast, when available.

3. current runway surface conditions, in case of precipitants or other temporary hazards;

4. changes in the operational status of visual and non-visual aids essential for approach and landing.

Information published by NOTAM or disseminated by other means may not have been received by the aircraft prior to departure or during en-route flight.

If it becomes necessary or operationally desirable that an arriving aircraft follow an instrument approach procedure or use a runway other than that initially stated, the flight crew shall be advised without delay.

At the commencement of final approach, the following information shall be transmitted to aircraft:

1. significant changes in the mean surface wind direction and speed;

Note. Significant changes are specified in Annex 3, Chapter 4. However, if the controller possesses wind information in the form of components, the significant changes are:

• Mean head-wind component: 19 km/h (10 kt)

• Mean tail-wind component: 4 km/h (2 kt)

• Mean cross-wind component: 9 km/h (5 kt)

2. the latest information, if any, on wind shear and/or turbulence in the final approach area;

3. the current visibility representative of the direction of approach and landing or, when provided, the current runway visual range value(s) and the trend, if practicable, supplemented by slant visual range value(s), if provided.

During final approach, the following information shall be transmitted without delay:

1. the sudden occurrence of hazards (e.g. unauthorized traffic on the runway);

1. significant variations in the current surface wind, expressed in terms of minimum and maximum values;

1. significant changes in runway surface conditions;

1. changes in the operational status of required visual or non-visual aids;

1. changes in observed RVR value(s), in accordance with the reported scale in use, or changes in the visibility representative of the direction of approach and landing.

b) What technology exists to help reduce the threat of mid-air collisions?

A traffic collision avoidance system or traffic alert and collision avoidance system (both abbreviated as TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC). It is a type of airborne collision avoidance system mandated by the International Civil Aviation Organization to be fitted to all aircraft with a maximum take-off mass (MTOM) of over 5700 kg (12,586 lbs) or authorized to carry more than 19 passengers.

Official definition from PANS-ATM (Nov 2007): ACAS / TCAS is an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders.

In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display (ND); in older glass cockpit aircraft and those with mechanical instrumentation, such an integrated TCAS display may replace the mechanical Vertical Speed Indicator (which indicates the rate with which the aircraft is descending or climbing).