In one of the comments on this answer regarding ILS category IIIc operations (or, rather, the lack thereof), it's mentioned that

There is no [radio] guidance for taxiing except the pilot's vision.

And, in an answer to another ILS IIIc question, it is stated:

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.


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.

Given that the ability to land is meaningless without the ability to taxi off the runway and to the gate (this is why, even though today's airliners are perfectly capable of IIIc landings, there are, in practice, no such landings, as no airport is equipped to taxi an aircraft in from a IIIc landing), why isn't there an "Instrument Taxiing System" to allow zero-visibility taxi?

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    $\begingroup$ A follow-me car may be considered a near-zero visibility taxiing guidance system. (Easy to set up and maintain) $\endgroup$ – Manu H May 30 '18 at 5:41

I believe that when it was created, Cat IIIc envisaged development of a zero visibility taxi guidance system using wires embedded in the taxiways. Never came to pass, probably because the cost and time to certify such a system, for both airports and airlines, wasn't worth the relatively rare conditions where it would benefit.

Such a system using GPS is a lot more feasible now, but still the glacial pace of the cert process means it would still take forever to implement.

  • $\begingroup$ So it wasn't worth it even for airports where crap weather is common? $\endgroup$ – Sean May 29 '18 at 16:06
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    $\begingroup$ Even if you have an airport that's fogbound all the time, you have to talk a lot of other parties, manufacturers, avionics makers, gov't authorities, etc., into spending years and hundreds of millions to certify a system for the benefit of you and a few others. Ain't gonna happen. $\endgroup$ – John K May 29 '18 at 17:14
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    $\begingroup$ Such a technology today would be IR or millimeter-wave imaging and it would be combined with low visibility landing/takeoff capabilities, so taxi would come along with it for "free". Business jets are leading the way in this capability, since they often fly to smaller airports. $\endgroup$ – user71659 May 29 '18 at 21:05
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    $\begingroup$ Also because the cert process is somewhat easier. Bizjets had flat panel displays long before transport category a/c did. $\endgroup$ – John K May 29 '18 at 21:44

If I were an airline executive in charge of determining the configuration of new aircraft being ordered from a manufacturer, and one of the options was an instrument taxiing system to allow so-called zero-visibility taxi, the aggregate cost of that system (purchase, maintenance, training, fuel to carry it) would have to be very low before I would consider it. My initial thought would be to reject it out of hand, but perhaps the ability to help a taxiing pilot navigate the taxiways of an unfamiliar airport would bring me around if the only cost was additional software for existing equipment. I say this as a pilot who on his first trip into Chicago O'Hare succeeded in getting some deservedly unkind words from a ground controller when I didn't turn when I should have and necessitated the rerouting of other aircraft.

In 10 years on the 747 I only once called for a follow-me car because of low visibility, and had the taxiway been better marked or my eye level lower I might not have needed that.

So it wasn't worth it even for airports where crap weather is common?

Consider the Arcata-Eureka Airport in McKinleyville, CA. The airport was deliberately built during World War II where they could depend on it being very foggy, and in that they succeeded. While the approach and landing were often challenging, there was never any real difficulty in taxiing if you were familiar with the airport.

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    $\begingroup$ You are right on. Airline management will avoid spending a single dime that doesn't generate a significant seat mile cost return, especially for an expensive system that might make only a marginal improvement in overall Schedule Completion Rate. In the regional airline industry, where the margins are REALLY tight, when it comes to modifying an existing fleet, operators would decline any improvement that didn't pay for itself in one year (it was once about 5 years). Unless there was an AD. $\endgroup$ – John K May 29 '18 at 17:42
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    $\begingroup$ @Sean I can't speak to current practice, but back in the 1990s there were often financial penalties if you didn't get the freight where it was supposed to be on time whereas you don't have to pay pax if they're late. While jumpseating on UPS, I remember captains nervously watching the clock, aware that the guy up in the cherry picker watching everything would log the time of their block out. At PDX it was 19:00 local for the flight I often commuted on. I was told that any time after that even 19:01 would get you some attention from management. $\endgroup$ – Terry May 30 '18 at 3:06
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    $\begingroup$ Normally, in the passenger airline world a "delay" is a leaving the gate more than 15 minutes late. This is "Dispatch Interruption Rate" and the normal standard is 99%+ but airplane types with technical problems can be lower than that, down around 97 or 98%, sometimes worse. Schedule Completion Rate is trips completed one way or another, and is always a higher number, much higher if an operator has spare aircraft available (common in the Regionals). $\endgroup$ – John K May 30 '18 at 3:23
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    $\begingroup$ @Sean I flew in 3 time critical freight operations. (1) There were thousands of retired Brits in the south of Spain. We picked up their morning papers at London Stansted around 03:00 local to be flown to Valencia and Palma de Majorca. I forget the exact times we had to have them at the destination, but the papers essentially became worthless if they were more than an hour or so late and the penalties reflected that. (2) On a USPS express mail contract we couldn't land before 06:00 local at Boston because of the curfew, but contractually the mail had to be at the P.O. before 07:00 local. $\endgroup$ – Terry May 30 '18 at 17:20
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    $\begingroup$ @Sean (3) On a UPS contract before they had their own airline, the penalties for non-compliance schedule-wise were severe. The problem was/is that each airplane coming into the sort has hundreds (thousands?) of packages that need to be routed to many other airplanes. Delaying the sort is not acceptable. If an airplane is late, it screws up everything. In case one was, they had a fleet of Learjets they'd call out to deliver the parcels of the late airplane. Very expensive. $\endgroup$ – Terry May 30 '18 at 17:29

I think such systems may exist already per the FAA's website:

Airport Surface Detection Equipment, Model X (ASDE-X)

ASDE-X provides more precise surface detection technology. While the ASDE-3/AMASS is based on non-cooperative sensor technology, ASDE-X integrates data from a variety of sources, including radars, transponder multilateration systems and Automatic Dependent Surveillance – Broadcast (ADS-B) to provide accurate target position and identification information and thus give controllers a more reliable view of airport operations. ASDE-X provides tower controllers a surface traffic situation display with visual and audible alerting of traffic conflicts and potential collisions. ASDE-X is installed at 35 airports in the U.S. For more information, see the ASDE-X fact sheet on the FAA website.

Airport Surface Detection Equipment, Model 3 (ASDE-3)/Airport Movement Area Safety System(AMASS)

ASDE-3/AMASS is a radar-based system that tracks ground movements and provides an automatic visual and audio alert to controllers when it detects potential collisions on airport runways. The system is usually referred to as ASDE-3/AMASS. ASDE-3 is the radar. AMASS is the software and hardware enhancement to the ASDE-3 radar that provides automated alerts and warnings to controllers. ASDE-3/AMASS is operational at nine airports.

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    $\begingroup$ That's just a system that lets controllers monitor movement of ground vehicles more precisely than traditional ground radar. No help for an aircraft that needs to be able to find its way around independently. I suppose you could have a system where ASDE-X interfaces with an on board aircraft system, but you are still talking about a massive and expensive cert program. GPS position can now be resolved down to centimeters so whatever system comes along will likely be a standalone GPS based system. $\endgroup$ – John K May 29 '18 at 19:31

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