Transponders | Product focus One firm has discovered a bug in its ADS-B receiver that occurs only when flying over the Null Island coordinate at 0°N latitude, 0°E longitude (not a real island). While that might never have actually resulted in a functional safety issue, it is indicative of the breadth of measures that high-end transponder companies must try to undertake to prove the robustness of their engineering to aviation authorities. Manufacturing With certification and batch manufacturing of UAVs taking off, safely critical avionics such as transponders are now being produced in facilities geared up for TSO-certified volume production (company owned factories and third-party contractors, depending on the organisation). To make a certified transponder requires undergoing frequent audits by regulators to ensure production processes, quality control, equipment, employee training, and traceability of tools and raw materials are all compliant with standards. Typically, this means every input part – chip, capacitor, PCB, radio, connector, fastener and so on – entering the production facility must be inspected. At the higher end, some manufacturers will use optical profilometers for contactless metrology, by which they can gauge uniformity between components in a batch, down to sub-millimetre details such as improper surface treatment on a housing or board component, and either clear or reject them for use in production. It is increasingly common that each part across inventories (no matter how small or how many of them there are) will be marked with some kind of barcode, QR code or serial code to ensure traceability. In certified aerospace, if a defect should ever be discovered in a specific batch of connectors, chips, resistors and so on, the manufacturer must be able to authoritatively state which transponders contained units from said batch. Following this will be different combinations of manual and automated processes (with automation increasingly the norm): robotic picking and placing of chips and capacitors, soldering of board-mount components, matings of boards together, mechanical assemblies of enclosures with mated boards, and possibly some burn-in testing to verify that a board has been assembled and flashed into good working order. The enclosures themselves will often be CNC-milled from aluminium or a similar metal (and coated) to extremely strict tolerances. While a transponder’s housing might seem its most unsophisticated component, it is in fact critical to creating a Faraday cage about the inner components and separating electronic circuits from each other. It also serves to contain or route the considerable heat output of the amplifier to a prudent location (so customers can then mount that to the skin of the aircraft for air cooling). Each step of the way, processes are tightly controlled with production data logged to show aviation authorities that manufacturing, assembly, programming and testing are executed in compliance with approved guidelines for making airworthy transponders. At the end of a production line, further metrology validates the quality to which the transponders have been assembled, including 3D vision and laser scans of surface-mount component arrangements and solder quality, and robotic probe tests of voltages and resistances across boards to check for connectivity or power-safety issues. Calibrations can be critical here for ensuring correct power levels throughout transponder-board assemblies. 93 Uncrewed Systems Technology | August/September 2024 This next-gen prototype will include multi-band ADS-B receivers, ACAS X capability and a low-power conspicuity device in a cost-optimised, single-board form factor (Image courtesy of Sagetech)
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