I've always wondered how would the theoretical (since no airport/plane has it) ILS CAT IIIc guide the plane off the runway? I mean from the perspective of radio signals. What component in the ILS system can help taxi off the runway after landing?

AVweb and other sources mention that:

CAT IIIc means an actual zero visibility landing because the airplane not only can land and stop itself, but can also automatically taxi in to parking.


3 Answers 3


There is no provision in the ILS system to provide for an auto-taxi or runway vacate. IIIc is just zero-zero and roll-out control, not auto-vacate as the linked AvWeb article seems to suggest. Its a logical extension of the FAA definition, however auto-taxi is not part of the CAT IIIc definition or system requirements. The only requirement is to get the aircraft on the runway and stopped.

FAA Circular 120.28C provides for the definition of a CAT IIIc approach:

c. Category IIIc. A precision instrument approach and landing with no DH and no runway visual range limitation.

Right now there is no airport approved for IIIc approaches because the aircraft would just sit on the runway, it has no way of taxiing in. Until an augmentation system like GPS with WAAS or LAAS, or the "Ground-Based Augmentation System" is developed further, automatic taxi is not there.

There is no provision in the existing ILS signals that allow for an aircraft to vacate the runway. GPS is as close as you can get, but that may be unreliable especially with larger aircraft like the Airbus A380 that doesn't have much play on either side, so GPS accuracy will have to be augmented with something. Additionally a system will have to be in place to avoid aircraft from colliding on adjacent taxiways or to manage traffic in and around the gate.

From a technical standpoint, this is a long way off, even with ground based radar systems, GBAS, and LAAS that are currently undergoing evaluation at several major airports world-wide.

Also see this FAA Document 8900.1 and Order 8400.13D

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    $\begingroup$ There is a lot of wishful thinking in that article, as no aircraft is capable of taxiing in by itself at the moment. Technically any aircraft capable of a IIIb landing is capable of a IIIc one, the difference is what happens when the landing is complete. Its certainly possible that NVG or FLIR could aid in a taxi in 0/0, but NVG and FLIR do have issues with perspective and depth perception. FLIR is actually becoming commonplace on some GA aircraft and have integrations for G1000/2000 panels. $\endgroup$
    – Ron Beyer
    Commented Jun 17, 2016 at 1:52
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    $\begingroup$ Just for reference, some aircraft have a "Rollout Mode" in their Auto-Flight systems that help the flight crew to stay centered on the runway centerline even with zero visibility. The Boeing 767 AutoFlight has this feature for example. $\endgroup$ Commented Jun 17, 2016 at 15:13
  • $\begingroup$ Related: "Advanced surface movement guidance and control system (SMGCS) manipulates runway and taxiway lighting to guide aircraft to gates." $\endgroup$
    – mins
    Commented Jun 20, 2016 at 22:09
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    $\begingroup$ @mins Somewhat related, but at zero-zero, they aren't going to be able to see the runway lights :) $\endgroup$
    – Ron Beyer
    Commented Jun 21, 2016 at 1:52
  • $\begingroup$ Umm, why couldn't ground radar be used to guide zero-visibility taxiing? $\endgroup$
    – Vikki
    Commented May 25, 2018 at 2:18

The other issue with ILS Cat IIIc not being operational is the inability of the ground support systems to function in zero visibility. So, in case an aircraft requires assistance (fire for example), the rescue systems should be able to reach him. This may not be possible.

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    $\begingroup$ Very interesting point! $\endgroup$
    – yo'
    Commented Sep 5, 2017 at 11:19


End of story. You're welcome!

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    $\begingroup$ Please cite a source for this. Otherwise, the answer amounts to "somebody on the internet said that..." which isn't really useful, and may be deleted. $\endgroup$
    – Ralph J
    Commented Apr 24, 2022 at 20:40
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    $\begingroup$ Additionally SHOUTING isn't very nice. Please use your inside voice. $\endgroup$
    – FreeMan
    Commented Apr 25, 2022 at 17:58

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