If I compare taxiing of airplanes with, for example, driving cars, drivers in the latter case regularly check the positions of their cars relative to others by using the different available mirrors. However, that is not an option in airplanes.

Just thinking about all potential possibilities, I imagine that airplanes probably rely on the airport control tower for making decisions that require the knowledge of the relative positions of other airplanes. Also, collision–prevention devices provide part of that information.

My question is:

How are airplane pilots aware of other nearby planes during taxi? Do they need that information, or is not useful for them as instructions are sent by the control tower?

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    $\begingroup$ Are you thinking of large, towered airports or small untowered airports? $\endgroup$ – raptortech97 Apr 5 '15 at 22:18
  • $\begingroup$ @raptortech97 I did not think that there was a difference between both. I am curious, why is that different? Small airplanes mean actually small size planes as well, does it? $\endgroup$ – Trebia Project. Apr 5 '15 at 22:33
  • $\begingroup$ It would appear they aren't aware of eachother in Dublin... and it wouldn't be the first time there either. $\endgroup$ – Danny Beckett Apr 6 '15 at 0:03
  • $\begingroup$ I know the British Airways taxi procedures. If one pilot needs to "look down" to complete a checklist, program something into the FMC etc, there is a positive check that the other pilot is looking out of the windows. At no point should they be taxiing without a good visual lookout. "See and be seen". $\endgroup$ – Simon Apr 6 '15 at 7:43
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    $\begingroup$ "car drivers are checking regularly the position of their car relative to others by using the different mirrors available in the car" - my experience in many different places is that this is substantially not the case, though I wish it were. $\endgroup$ – Esoteric Screen Name Apr 9 '15 at 3:29

At a large airport, all aircraft movements are coordinated by the ATC tower on the ground frequency. Aircraft should never move without authorization from the controller. The tower will issue instructions to aircraft that might look something like this:

Taxi to Gate 1 via Alpha, Alpha 1, Lima 3, cross runway 24, hold short Delta.

These names correspond to markings on the ground that match up with the airport taxiing maps. By talking with the pilots, the controllers are able to build up a map of where aircraft are. It also helps that they can look out the window and see the aircraft on the ground.

At airports without a tower, taxiing isn't much of an issue. There aren't many planes around, and there's generally only one runway and not many taxiways. Nevertheless, aircraft taxiing when there is no ground controller comply with "see and be seen" by looking outside and turning on aircraft lights. Furthermore, if the aircraft has a radio, it should self-announce its movements on the ground.

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    $\begingroup$ So pilots are taxiing "blinded", following instructions of controllers like board game? (conceptually I mean :) ) $\endgroup$ – Trebia Project. Apr 5 '15 at 22:35
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    $\begingroup$ @TrebiaProject. Basically. Obviously, if they see a plane ahead stop they're not just gonna ram into it because the controller didn't tell them not to, but they more or less just do what the controller tells them to. They're almost like chess pieces. $\endgroup$ – raptortech97 Apr 5 '15 at 22:44
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    $\begingroup$ @Trebia: Pilots can still look out their windows and see where they're going. There's not the same need for mirrors to look backwards etc. as there are for cars, because taxiways are single-lane anyway -- there's no overtaking. $\endgroup$ – hmakholm left over Monica Apr 5 '15 at 22:47
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    $\begingroup$ @HenningMakholm still some incidents happen because ground operations. The more people looking to the information, the best. I was thinking as well measuring distance, I remember a couple of incidents where a wing hit the tail plane of a parked airplane. Thanks! $\endgroup$ – Trebia Project. Apr 5 '15 at 22:50
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    $\begingroup$ @TrebiaProject. In short - not particularly frustrating. It's kind of opinion-based, so perhaps not a great question topic - but please feel free to join us in chat to discuss! $\endgroup$ – NathanG Apr 6 '15 at 1:22

To expand on the answer from raptortech97, taxiing an aircraft is similar to driving a car. Instead of traffic signals, the ground controller tells the pilot where to go, but the pilots should still be looking out the window and remain aware of aircraft around them. As with aircraft in the air, the ground controller will anticipate conflicts between aircraft and give them instructions to avoid issues.

A controller will instruct an aircraft when they need to yield to others:

...give way to company 737 on Delta.

And possibly advise the other aircraft as well:

...continue on Bravo, company will give way to you at Delta.

Often aircraft are going to the same place (like the active runway), so it can simplify things to just tell pilots to follow other airplanes:

...follow the company 737 on Delta.

In conditions where aircraft will be taxiing, visibility is generally good enough that pilots can see other aircraft. If visibility gets worse, the ground controller will be more cautious, knowing that the aircraft may not be able to see each other.

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