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Upon receipt of taxi instructions at large airports, do pilots ever forget or misremember these instructions, are there any documented instances of this and how much better is a 'follow the greens' type procedure for your workload and memory.

I'm concerned primarily with human memory limitations and how simply following a green centreline reduces the human workload on pilots.

I understand pilots have kneeboards and maps which certainly reduces risk of this happening but it would be interesting to hear if this is possible / has happened before ?

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    $\begingroup$ Some airports have "follow me" cars to help pilots navigate complex taxiway systems. A lot less high tech, no idea how effective it is, but supposedly the driver is more familiar with the airport so is less likely to get things wrong. A bit like maritime pilots, but without actually boarding or piloting the plane, just showing the way. $\endgroup$
    – jcaron
    Commented Oct 30 at 15:02

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Anything that might go wrong, probably has, in the history of aviation, and things like mis-remembering a taxi clearance has certainly happened a lot.

If by "follow the greens" you're referring to a system that activates the in-pavement centerline lighting, segment by segment, for each aircraft's specified route, that would be very cool and an absolute game-changer. I fly to major airports in the U.S. every week, and I've yet to see such a system in use for getting you from the gate to the runway or vice versa.

If the clearance is longer than about two taxiways (i.e., leave the ramp on A, right turn on B to runway 28), I'll typically highlight the taxi route on the airport diagram on my EFB before starting to taxi. If the clearance is particularly long (Chicago O'Hare is notorious for this), I'll either write it down first, or type it into the FMC scratchpad to refer to as I'm highlighting. And, always, confirm with the other pilot what we're about to do.

And every so often, we still have to ask Ground to repeat or clarify some part of it. Which works fine.

But unless it's the exact same clearance as the last fifty times I've taxied here, trusting memory for a lengthy set of instructions is setting yourself up for a mistake.

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    $\begingroup$ Wow I've never seen an airport as complex as ORD until now that's a great example I can use. "follow the greens" refers to A-SMGCS level 4 equipped airports which includes conflict resolution, automatic planning & guidance. But I'm surprised to hear somewhere as busy as Chicago doesn't have this. The results from tests in Europe at least show massive decreases in fuel consumption, better pilot SA and less controller workload. $\endgroup$
    – Dylan
    Commented Oct 29 at 13:28
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    $\begingroup$ @Dylan massively expensive, and such things in aviation take time to be adopted. $\endgroup$
    – John K
    Commented Oct 29 at 15:03
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    $\begingroup$ An example of follow the greens at Incheon Airport in Korea. Eurocontrol has standard phraseology for this e.g. “Callsign, Follow the Greens to Holding Point N2 Runway 27 (or Stand 123).” $\endgroup$ Commented Nov 1 at 6:46
  • $\begingroup$ That video suggests it reduced the 'mis-entry into taxiway' statistics from 8.8 per month to 1.8 per month, a 70% drop. $\endgroup$ Commented Nov 1 at 16:42
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The worst aviation accident in Italy occurred in 2001 at Milano Linate airport, on the ground.

A taxiing Cessna Citation crossed the runway after a taxiway error, on a foggy day at the same time a MD-87 was taking off. The Citation pilot had taken R6 instead of R5 at this branch:

Taxiway selection at Linate Airport

Source: ANSV Investigation report.

From the investigation report:

The obvious consideration is that the human factor related action of the Cessna crew – during low visibility conditions - must be weighted against the scenario that allowed the course of events that led to the fatal collision; equally it can be stated that the system in place at Milano Linate airport was not geared to trap misunderstandings, let alone inadequate procedures, blatant human errors and faulty airport layout.

The clearance was not long:

DeltaVictorXray taxi north via Romeo 5, QNH 1013, call me back at the stop bar of the…main runway extension.

But the readback was not compliant, neither mentioning north or the stopbar:

Roger via Romeo 5 and…1013 and call you back before reaching main runway.

This case was a combination of errors and technical failures, despite the airport being one of the busiest in Italy. A visual path of some sort would have been sufficient to neutralize the problems and prevent the fatal consequences.

There is an episode of Air Crash Investigation about it: The Invisible Plane.

More about A-SMGCS and SMAN systems:

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    $\begingroup$ On Linate, the stop bars were malfunctioning and they were so used to this that nobody cared. So while it is a great example of how taxiway confusion can lead to an accident, it's not so clear that more technology would have changed anything. $\endgroup$
    – Geir
    Commented Oct 30 at 4:07
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    $\begingroup$ I think using a different font for the markings could have changed things; to me "5" and "6" look too similar on the photo. $\endgroup$
    – U. Windl
    Commented Oct 30 at 8:59
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    $\begingroup$ @Geir: The stop bars were permanently ON, meaning mandatory stop, the pilot didn't not call back when reaching (the wrong) one, as required by the clearance. The stop bars played no role. After the accident, the taxi procedure was changed: "without ground radar functioning [...] with visibility less than 200 meters [...] only one movement at a time shall be allowed on the movement area with the assistance of the Follow-me to comply with national regulation, and is more or less the same than a visual guidance, confirming this system could help change the outcome. $\endgroup$
    – mins
    Commented Oct 30 at 11:13

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