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For commercial aircraft, precise landing aid systems (ILS, GBAS) are required for autolanding, but these navigation systems are too expensive to be used for UAV operations. However, a lot of UAV OEMs have claimed and demoed landing the fixed wing UAV at a runway which is typically used for a Part 23 aircraft.

  • How do these fixed wing UAVs perform and autoland?
  • What kind of landing aided system are installed on the ground or on board?
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  • $\begingroup$ UAV - U = unmanned, not necessarily unpiloted. $\endgroup$ – CatchAsCatchCan Mar 7 at 3:22
  • $\begingroup$ How big are the UAVs that were demoed? Any examples? Please add (if possible) to the question. $\endgroup$ – ymb1 Mar 7 at 7:29
  • $\begingroup$ Similar to a Part 23 general aviation aircrafts, 1 to 5 tons $\endgroup$ – VvV Mar 7 at 7:30
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Each project will have its own specifications. Military UAVs will have different use cases from civilian ones, and, as the comments mention, unmanned does not mean unpiloted.

Most of current UAVs are remotely piloted, meaning that there is a front facing camera relaying images to the ground, where a pilot will command flight adjustments to the vehicle to keep it aligned, no special equipment involved (except for the air-ground communication apparatus). The aircraft will be equipped with the usual inertial sensor unit(s) and GNSS receiver(s).

For situations where you might have an unpiloted aircraft (that are extremely rare today), it is still solvable by simple INS + GNSS, with the additional requirement that you will have to accurately measure the position of the runway in the GNSS reference system (published charts are not precise enough, as they are created for eye-bearing humans, that can correct the course by sight). This is the method we used and we landed 2 meters from the centerline (the two pilots where there for safety, being it the first attempt).
Other projects might include ground-based aid signals akin to an ILS system.

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  • $\begingroup$ 2 meters, cool! So no ground landing aided system is used for the auto land and it is purely done by onboard navigation and control equipment? If it could be done by onboard equipment, then why ground aided system like GBAS/ILS are must have to support auto land in the industry? $\endgroup$ – VvV Mar 7 at 8:14
  • $\begingroup$ @YoungL because different situations require different levels of certainty. If the GPS fails during the landing, what would you do without ILS? $\endgroup$ – Federico Mar 7 at 8:22
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    $\begingroup$ @YoungL because if a UAV runs off the runway, a few million $ is wrecked and you may close the runway for an hour or two for clean up. If a commercial airliner runs off the runway, it might be hundreds of millions in damage, plus hundreds of lives potentially at risk. With higher risk comes the necessity of higher safety margins provided by ground-based systems. $\endgroup$ – FreeMan Mar 7 at 15:12
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A don't know what systems they're using (probably classified). I do know however that military GPS has the "password" to decode the additional GPS frequencies unavailable for civilians, and this gives GPS a much precise location. That should be enough to land a UAV.

Civilians can't use this, but most of the absolute error is due to changes in the ionosphere. Relative precision is a lot better. So if you have a receiver at the airstrip, and you broadcast your location, the UAV can calculate its relative position to the airstrip a lot better. This must be good enough as well. Actually, GPS has around 3 meters (10 feet) of error in the open sky on flat ground - incidentally most airstrips has these features - and airstrips are quite big. Smaller UAVs could land based solely on GPS without external help on airstrips built for bigger planes, because that 3m difference is good enough.

(Those are based on how I would do it. I don't know enough about UAVs, but I have experience with different GPS systems.)

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