From: email@example.com Organization: Cambridge University Engineering Department, UK Date: 30 Oct 94 21:29:41
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According to 5-11 October 1994 issue of Flight International, Martin Marietta is attempting to market a new approach and landing aid designed to chnage the approaches are made. The system is called APALS (Autonomous Precision Approach and Landing System). The way it works is it enhances the aircraft's existing weather radar to produce ground images of sufficient resolution to allow matching with a terrain database. The correlation of actual radar image and the database scene produces an error which is used to update the aircraft's Inertial Navigation System (INS). The new position is used to predict what the next radar image will be, and so on. APALS does not require ground aids such as ILS or airport lighting but does require an airborne global-positioning-system (GPS) and the creation of a terrain database for all approaches to be flown. Full benefits of the system can be realised if used with a head-up-display (HUD) which recreates an image of the approaching runway including touchdown markers. I would like to point out the advantages and disadvantages of this system. Firstly the fact that it does not require any ground aids means that you can land your aircraft on any airport in case of emergency provided the system database has the image data. This system is ideal for airports like Katmandu in Nepal where there are limited ground aids and poor visibility. This system could be another solution to the replacement of ILS in Europe where the VHF band will reach saturation by 1997. However the idea if being totally independent of ground aids can be dangerous in the case of system malfunction. Due to its reliance on GPS the accuracy cannot be guranteed unless high acurracy high cost GPS recievers are used. The database should cover all of the main airports throughout the world if it is to be used internationally and the terrain data should be constantly updated since features such as roads, building edges are used for correlation. All of this means that the operating cost of APALS could be very high and higher than operating the existing ground based approach and landing systems. Any comments are welcome. It should be noted that this article is intended to point out the advantages and disadvantages of using APALS and not to criticise Martin Marietta's products.