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How resistant are those systems with respect to tampering with the physical antenna ? Would someone tilting the antenna a few degrees towards the ground with a

• t0mas88 7y ago
  They are positioned literally at the runway, so the first protection is that you're probably not going to get to them with a screwdriver. False glideslopes occur for many reasons, not just tilting the antenna, but also reflection or approaching them from outside the coverage area (the signal can leak in other directions). The protection is mostly in the check by the pilots that the altitude based on air pressure is correct for the indications. And there are regular calibration flights where the signals are checked against for example GPS position. Apart from that the signals are monitored on the airport itself, but I'm not sure that would detect tilting it down just a little bit. I think it's more for other signals interfering or the transmitters failing in some way. Edit: Oh and we have our GPS (or DME based) ground speed visible in the cockpit and know the descent rate in feet/minute (also displayed on the primary instruments) to expect for a correct glidepath with that speed. So if the descent rate is "off" almost any pilot would notice and start to think about what's causing it. If you can't figure out why the combination of data doesn't make sense, go around. That's basically in the first lesson of instrument flying.