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Aviation History
1981
1981 - 0099.PDF
FLIGHT International, 10 January 1981 93 IAL delivers first Stratus IAL is installing its first Stratus com munications switching system at the Abu Dhabi New International Airport (Adnia). Stratus is a microprocessor- based switching system designed to give flexibility and high operating capacity and speed. Although IAL's old 7500 electro-mechanical switching system remains in production for small applications, Stratus will re place it effectively from now on. There are two versions of Stratus —the space division system and the time division multiplex system. Adnia is being fitted with a space division system, which comprises a pattern of cross-point switches linking each con troller's console with the stations with which the controller needs to be in touch—the airband frequencies, flight information centre, other con trollers and emergency services. The switches are field effect transistors. When the controller presses a button to select with whom he wishes to speak, the signal is fed to a micro processor which carries out the switching necessary—it breaks con tact with whoever he was talking to before and connects him with his new radio frequency or telephone line. When the connection has been made, the light on the selector but ton comes on, giving the controller a positive indication that he is in contact with the desired person. Each console has its own microprocessor, all the microprocessors being con nected by a triplicated data bus. Also connected to the data bus is a diag nostic microprocessor which indicates the failed board in the event of a mal function. If one microprocessor fails. either one operator is lost or three to four channels become inoperative. The space division system is limited to around 30 channels—the Adnia system has 28—because of the large number of cross-point switches required. The time division multiplex system is intended for larger applications where, it is impossible to provide an individual switch for each combina tion of users. In this version the operator's speech is encoded in to a pulse code modulated signal and is passed along a data bus. A flag signal to indicate the destination accom panies the electrical signal represent ing the speech, so that the message leaves the data bus at the appropriate junction. The message is then trans lated from digital form back to speech before reaching its destina tion. Since the time division multiplex version of Stratus is purely elec tronic, it can deal with far more chan nels than its electro-mechanical counterpart. IAL says that the multi plex version of Stratus has a poten tial for coping with over 1,000 cross- points. Each console has its own microprocessor which is connected to the others via a triplicated data bus in the same way as in the space divi sion version. A diagnostic computer is also included. IAL has received orders for the multiplex version from a Middle-Eastern country for a mili tary application, and from Britain's New Scotland Yard. These orders are worth £6-5 million and £1 million respectively. A feature of the multiplex version London's air traffic control centre at West Drayton is a potential application for the IAL Stratus switching system. IAL estimates that around 360 channels will be needed to connect the area controllers with each other, the aircraft, emergency services, airports and flight information centres. Such an order could be worth £10 million 111 m 1 is an additional supervisor's station, which allows him to monitor his sub ordinates, intervening if necessary. The supervisor can select any frequency, rather than working on preselected frequencies like the other controllers. He can also select the frequencies which the other con trollers are using if required. The Stratus switching equipment is housed in a standard 19in rack cabinet which is usually 7ft tall to allow for future expansion. This is connected to the controller's console by only one set of wires, which makes plugging-in easy and allows remote operation via land-lines, radio or satellite—particularly useful for mili tary applications. When Flight visited IAL's South well factory several consoles for the Adnia programme were visible, to gether with conventional 7500 ter minals for Nigeria and six NDBs. IAL makes up its circuit boards from stan dard components, and it invested in a £U million computerised test rig about a year ago. A unique plug-in jig has to be used for each board to be tested, around 50 jigs being neces sary for testing the Stratus boards. When the jig is fitted to the test unit, the circuit board is placed so that it rests on gold contacts. The computer tests the board and gives a print-out listing the faulty components within 30 to 40 seconds for a purely digital board. It keeps the results in its memory for three years. IAL has found this test gear very cost-effec tive, since the company estimates that an in-the-field repair made after delivery costs 100 times more than a similar repair made before the board leaves the factory. IAL has achieved sales success with Stratus already—the company has an order book amounting to £8-5 mil lion, compared with an investment of only £1 million so far. Other sales possibilities exist, the next major potential order for Stratus being the switching system for London's air traffic control centre at West Drayton. Around 360 channels will be needed, and the contract could be worth £10 million altogether to whoever wins it. The availability of microprocessors has enabled IAL to develop a switch ing system which offers greater capa city and operating speed than the old electro-mechanical systems, while in corporating the inherent flexibility and reliability of microprocessor technology.
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