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From ICAO Annex 2:

4.2.3.1 A horizontal white dumb-bell (Figure A1-4) when displayed in a signal area indicates that aircraft are required to land, take off and taxi on runways and taxiways only.

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4.2.3.2 The same horizontal white dumb-bell as in 4.2.3.1 but with a black bar placed perpendicular to the shaft across each circular portion of the dumb-bell (Figure A1-5) when displayed in a signal area indicates that aircraft are required to land and take off on runways only, but other manoeuvres need not be confined to runways and taxiways.

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The text from Annex 2 is clear. For the first one, aircraft are required to land, take off and taxi on runways and taxiways only. But when is this not the case? Why would you need a signal to specify this - isn't it normally the case that you need to land, take off and taxi on runways and taxiways? Same question for the second one, basically.

Please try to elaborate on the text from Annex 2, and give examples of practical use of these two signals.

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  • $\begingroup$ One possibility is if you are allowed to taxi through the grass... $\endgroup$ – Ron Beyer Aug 30 '16 at 15:33
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    $\begingroup$ One example would be Thruxton in the UK where I learned to fly helicopters. We would take off, land and taxi pretty much where we wanted, giving way to the planks of course ;) $\endgroup$ – Simon Aug 30 '16 at 16:11
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These symbols are intended for old-fashioned "airfields" which just have a large grass area instead of a runway. This used to be the norm before the increasing weight of aircraft in the Second World War. The whole surface of such a site is suitable for the movement of aircraft, so you don't need to be on a particular runway or taxiway: you can just take-off and land in the wind direction.

This was the norm when the ICAO rules were drawn up, so the case of only being allowed to operate on a particular surface was the exception then, not the rule. The runway-only aerodromes probably wouldn't have their grass in good condition, so it would be dangerous to land on grass: you might put your undercarriage in a rabbit hole. Back then, when most aircraft didn't have radio, you would have needed a signal at the unusual runway-only aerodromes so that visiting pilots wouldn't assume it was OK to land where they liked. The signal would more likely be a permanent fixture at these aerodromes, rather than something flown at particular times.

Nowadays, the only situation where this is common is in glider flying. At a popular glider site, there might be a hard runway provided for the tow airplane or for winch launches, but gliders can land anywhere on the aerodrome. Or there might be a marked (hard or grass) runway for take-off and landing, but no taxiways at all: you just vacate onto the grass. As Jay Carr points out, a fly-in or a gliding competition would be an example of when a particular aerodrome might change from one to the other, but that might go either way. The same aerodrome where normally everyone lands on grass might be worried about the condition of the grass at a high-traffic event (and about the safety implications of a variable landing direction), so they might have people stick to the runway for that one event.

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  • $\begingroup$ Hi, both signals are normally used in a no controlled airdrome, the ones which has no radios aircraft operating. <BR> It will indicate to the pilots there are parts of the movement area unserviceable, can be due to softness or wet, most probably in grass fields. <BR> In case of hard surface, indicates to stay in the runway or taxiways, do not taxi or park the aircraft outside of the hard surfaces.<BR>Both signals are time-limited due to weather. <BR> This kind of signal must be used with careful in airport that have more than one runway, it can be dangerous to identify the correct RWY. $\endgroup$ – Manolo Sep 5 '16 at 23:51
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I keep thinking of some of the big fly ins (like Air Venture in Oshkosh) where pilots are allowed to park on the grass.

During the fly in they might use that second symbol (dumbbell with stripes) to let people know it's okay to park on the grass, but you still need to take off, land, and taxi on official taxiways and runways (as defined by the event rules). Thus significantly increasing capacity during the event.

But during other weeks that same airport probably doesn't want anyone taxing onto, or parking on, the grass. So they would display the first symbol (dumbbell with no stripes) to remind everyone that the exception is gone, and the rules have changed back to what you would normally expect at most airports. Thus people would be aware they need to stay off the grass and use official tie down areas for parking.

In essence, I think the first symbol exists mostly because of the second one. At airports where there are occasionally exceptions along the lines of those described above, they may also want a symbol to help pilots know when the exceptions are not in effect.

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  • $\begingroup$ Thanks for your answer - I appreciate it. While you do present a reasonable explanation, I was hoping for an answer from someone with practical experience and/or appropriate sources. It sounds like your answer is mostly an educated guess. If this is not the case, please feel free to update the phrasing to reflect that. $\endgroup$ – J. Hougaard Sep 1 '16 at 17:14
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    $\begingroup$ @J.Hougaard It's just an educated guess, though I did my best to display the logic I'm using. If it makes you feel any better, I've been patiently waiting for someone with actual experience to show up and explain it to, just to check my logic, ya know? You might try posting a link to this question on www.redddit.com/r/flying to see if you can draw someone in who might know. $\endgroup$ – Jay Carr Sep 1 '16 at 17:17
  • $\begingroup$ @J.Hougaard In fact I felt so strongly about it, I put it on r/flying myself. Hopefully it draws someone in... $\endgroup$ – Jay Carr Sep 1 '16 at 17:25
  • $\begingroup$ Great, let's hope so! :) $\endgroup$ – J. Hougaard Sep 1 '16 at 17:26

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