Let Your Ears Have Wings

1. The tarmac starting point.

2. The waypoints.

3. The destination.

INS does the rest, with a very small error margin. Take, for example, the ten-hour flight from Sydney to Honolulu, covering about 5000 nm. If INS is used, and during the flight, the captain makes no en route corrections to allow for drift of the aircraft, the aircraft would only be 8 miles off-track from its destination, Honolulu International Airport. The captain could easily see the runway from that distance in reasonable weather conditions.

The INS consists of gyroscopes, accelerometers and computers. Using the INS hooked up to the automatic pilot, course corrections can be made in flight, so that navigation is pinpoint.

Omega Navigation System

The most technically advanced navigation system currently in use by the airlines is Omega, based on the low-frequency radiowaves from 8 LF stations scattered strategically across the world.

Omega is used equally efficiently by airlines, shipping and submarines. The 8 low-frequency (LF) stations emit three pulses every ten seconds, each pulse lasting for one second. Atomic clocks at each LF-radio station site regulate the spacing and duration of the pulses. Synchronised computers on board the aircraft, ships and submarines transpose the 8 signals into a cross-reference position-fix, and display the final position readout in latitude and longitude on a digital-display monitor. The Omega position is accurate, without any need for corrections, to an unbelievable 2 miles! Omega certainly is the navigation system that will be adopted by most world airlines in the future.

The Selcal System (Selective-Calling)

Selcal is an alarm device that rings in an individual aircraft, following a push-button activation of the equipment by ground personnel. Selcal is a computer-based four-letter calling code, similar to a telephone number, with each aircraft having its own distinctive (and permanent) Selcal code.

For example, a Qantas Boeing 747 airliner may have little Selcal Code of E-G-Q-F. (In fact, no presently-operated Qantas aircraft has this particular code. ) On activation from the ground station, an amber light flashes on, and a two-note paging chime is seen and heard on the aircraft’s fight deck, requiring the flight crew to answer the radio. You will hear the flight crew on the airliner respond in this way: ‘Qantas four answering Selcal. ‘ The range of Selcal is as far as HF radio contact is maintained. The Selcal Chimes ring on the flight deck under the Second Officer’s, or Flight-Engineer’s table. At the same time, on a radio panel forward of the throttles, an amber light flashes ‘on’. The Selcal system allows airliners to be paged individually, as though by using a kind of aerial telephone. Each aircraft has its own individual call-letter code, assigned to aircraft worldwide by Aeronautical Radio Incorporated (ARING) in the USA, who also maintains the register of such allocations. Each four-letter Selcal code is clearly displayed on the flight deck of the aircraft on a metal plaque, along with the aircraft’s registration number. The Selcal Message is received automatically after activation from the ground, with an on-board computer inside the Selca! equipment decoding the chimes that have been broadcast.

Selcal only activates in the aircraft that has been called. The equipment on all other aircraft flight decks, that are using the same air/ground radio frequency, does not activate. Thus it is possible to have airliners maintain a ‘Selcal-Watch’, where they may in fact not actually listen to air/ground broadcasts, but wait to have their Selcal Equipment is activated before they attend to the radio. The real beauty of Selcal is that flight crews are not disturbed needlessly. Some airlines, such as Qantas and Air New Zealand, instruct their captains to make HF radio calls to ground stations approximately 15 minutes prior to departure so that the reliability of the equipment is assured before takeoff. Occasionally, the Selcal code belonging to the aircraft will be offered on the radio to the ground station, in case it has not been included on the flight plan.

Following this initial pre-flight, or ground check, the Selcal code will be passed by Compac-cable from ground station to ground station across the route, in preparation for the arrival of the aircraft inside each ground station’s flight-information region (FIR).

Position Reporting

Position reports are made either in a type of code, or by using Latitude and Longitude. Greenwich Mean Time (GMT), or ‘Zulu’ time is used throughout the world in a// aviation, either local or international. On HF, position code names are merely pseudonyms for waypoints along the route. For example, Porgy is 31 degrees South, 158 degrees East, over the Tasman Sea, off the east coast of Australia. Most airliners in Australian FIR’s provide position reports using waypoint codes. To enable use of computers for flight-planning etc. , most waypoint codes are being changed to five letters.

Each waypoint name, selected by the International Civil Aviation Organisation (ICAO) is designed to combat ambiguity when pronounced on the radio-telephone (R/T) by aircrews and ground personnel. The ease with which these names can be understood will be of great assistance to you as you follow airliners along the airways to their international destinations.

Air New Zealand are the only world airline to include in their spoken-air-reports (AIREPS) positions firstly in waypoint code, then in Latitude and Longitude, to ensure correct reception of the message. The Latitude and Longitude is also the position at which the Air New Zealand flight crew has taken the spot-wind reading.

Tracking Airliners by Radio

Sometimes, up to six or more ground stations share a common frequency family for air/ground radio-telephone-circuit communications. For example, Sydney, Auckland, Nadi, Tahiti and Honolulu, plus numerous Pacific Islands share 2945, 5643, 8847, 13300 and 17904 for operations with aircraft overflying the South Pacific Ocean and Tasman Sea. Ground stations are either AM, or Single-sideband (SSB), and average 5000 watts of power. . Aircraft on airline routes have AM, or AM and SSB capabilities, and average 150 watts of output power. The upper sideband mode of transmission is used on SSB. To follow a particular aircraft, such as the evening flight by Qantas from Sydney to San Francisco, callsign and flight number ‘Qantas 3’, tune from Sydney to Honolulu on 5643 Khz, then from Honolulu to San Francisco on 5603 Khz. Only two en route HF frequencies for 10,000 nm, or 15 hours of flying-time!

Distress Signals From Aircraft

Whether on VHF, UHF or HF; an aircraft usually notifies its distress on the particular route frequency it is working on at the time.

If an aircraft departs Sydney, and changes from CONTROL TOWER frequency to DEPARTURES, then experiences a sudden engine failure, he will use the DEPARTURES frequency for his MAYDAY call. On HF, the procedure is identical. If an aircraft is working on a 5000 Khz en route frequency, he will use that to communicate any trouble being experienced in relation to the safety of the aircraft.

The pilot may also choose to put out a voice call for assistance on the international DISTRESS frequency for aircraft, 121. 5 Mhz. This frequency would normally be associated with VSB signals, or VHF Survival beacons, activated automatically in time of sudden trouble. All aircraft on trans-oceanic flights monitor 121. 5 Mhz, in case an aircraft in their area has an emergency. The moment a DISTRESS signal is picked up, the Search and Rescue phase is put into immediate action. A distress call is termed ‘MAYDAY’. An urgent call is termed ‘PAN’. PAN has priority over all other radio calls except MAYDAY.

Mayday Calls-Content

In addition to the MAYDAY signal, usually spoken three times, an aircraft in distress should be operating on the primary radio frequency, name the station addressed, the aircraft identification call sign, the nature of the distress condition, the intention of the pilot-in-command, and the aircraft’s present position, flight level or altitude, and heading, either magnetic or true.

Pan Signal-Content

The same procedure as MAYDAY is adopted, but the word PAN is spoken instead of MAYDAY, and after the aircraft’s callsign has been given, the nature of the urgent situation is stated.

Selection of a Good VHF Radio Receiver

A small set is required, capable of portable operation (for trips to airport perimeters), with excellent sensitivity and selectivity. Sensitivity means the ability to ‘pull in’ weak signals, while selectivity means the ability of the receiver to select the exact station you wish to listen to, on a crowded radio band. If you don’t wish to spend more than a few dollars, choose any sensitive portable receiver containing the VHF Airband 108-136 Mhz, priced between twenty and one hundred and twenty dollars, in Australia.

If you buy a set priced higher than eighty dollars, make your selection one that includes a ‘SQUELCH’ muting control, enabling you to effectively silence the otherwise noisy VHF receiver until the station you wish to monitor begins to transmit.

Most Reliable VHF Airband Receivers

The Dick Smith D-2836 AM-Airband portable receiver is an extremely sensitive, yet cheaply priced receiver, or you could consider the equally good Radio Shack TANDY Patrolman CB-60, or Patrolman 50 receivers. Dick Smith’s receiver does not include a squelch control but retails for approximately twenty-four dollars. The Tandy models both have ‘squelch’, but they are placed between sixty and ninety dollars. If you wish to spend a little more, say from four hundred to five hundred dollars, the purchase of any of the excellent programmable, d1g1tal-readout VHF Airband FLIGHT SCANNERS will result in your becoming the proud owner of the ultimate VHF monitor receiver.

One excellent example from the wide range of very efficient airband scanning receivers is the Regency Digital Flight Scan, which retails at approximately four hundred dollars. This receiver has the potential for receiving 720 domestic and international aircraft channels, keyboard push-button frequency programming (no crystals required), squelch control, frequency memory unit for storing favourite frequencies, and full digital readout from an LED, or l1ght-em1tting-diode.

Selecting a HF-Bands, General-Coverage Communications Receiver

Good receivers for HF listening are priced similarly to the range of VHF digital-readout flight scanners, at around four hundred dollars in Australia. Make sure you select a receiver with LED digital-frequency-readout, or that it has a direct-dial-readout facility accurate enough to tune as close as 5 Kz from the frequency you wish to monitor. For example, if you wish to motor 5643 Khz make sure your receiver choice is capable of tuning at least to 5638 and 5648 with accuracy. Even though you will not be ‘right on the mark’, you will still hear the bleedover signal from 5643. Digital0frequency-readout LED Units should be accurate to 1 Khz. Using both these types of tuning devices, you can confidently tune up stations while they are not making transmissions and wait for their next call to be made.

Your receiver must also ideally have an antenna trim control, so that any random-size receiving antenna can be matched to your receiver for best results. It goes without saying that like VHF receivers, HF communications receivers must have both excellent sensitivity and selectivity. Otherwise, steer clear!

More Notable HF General-Coverage Communications Receivers

My particular favourite is the Trio-Kenwood R-1000, a truly superb receiver. Other good buys are the National Panasonic DR-28 or DR-49, the Tandy ‘Realistic’ DX-200 or DX-302, or the Yaesu Musen FRG-7 or FRG-7700, the latter two being available from Dick Smith retail outlets.

The Trio-Kenwood R-1000, National DR-28 and DR-49, the Tandy DX-302 and the FRG-7700 are all equipped with LED digital-readout facility. The balance of the receivers have direct-readout or manual-readout. Tandy’s DX-200 uses a device called a crystal calibrator for tuning accuracy. If you purchase a receiver with a crystal calibrator fitted, consult your operating handbook for detailed instructions concerning its proper use, so that your station-tuning can be ‘right-on-the-mark’, eliminating so-called ‘finger-trouble’. DIGITAL DIALLING of frequencies is perfection, but DIRECT-READOUT can be almost as good, with a practised, competent operator!

Points to Remember While Operating Good HF Receiving Equipment.

1. Read your operating manual supplied with your receiver thoroughly. Know your receiver.

2. Use a properly-earthed antenna system, with coaxial-cable lead-in wire to your receiver.

3. Insulate your antenna with plastic strips where it is strung-up.

4. Cut your antenna to the correct length for the frequency you mainly wish to monitor (using your guide printed in this series).