On UK airport charts like the one below for Manchester (EGCC), what is the difference between an identifier with white lettering on a red square and one with yellow lettering on a black square with a yellow outline?
1 Answer
Both are hold position signs; white on red is "to protect a priority route".
— UK AIP GEN 2.3
Below is the red J2 and black J1 as seen from the cockpit (YouTube):
The usage description below shows inconsistency with the map, which hints at a gradual phasing out (see 2021 update below):
Where it is considered necessary to locate taxi-holding positions other than at runway/taxiway intersections – for example at taxiway/taxiway intersections in order to protect a priority route – the holding position should be identified by a single sign located wherever practicable on the left side of the taxiway. The sign consists of a combination of the letter designating the taxiway and a number identifying the hold position e.g. A1, A2, B2 etc. in white on a red background. An example of an intermediate taxi-holding position sign is shown at figure 7.13 (F).
2021 update
At Manchester, only yellow on black is used now. Latest AIP and CAP 168 still have the white on red option.
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$\begingroup$ Thanks! I like that you referenced a YouTube too. When I first looked at this, I thought the opposite - that the yellow / black were optional, and that the write / red were mandatory (since all things regulatory in the US are in red). $\endgroup$ Jun 17, 2018 at 0:44
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$\begingroup$ @slantalpha: I've updated the answer. The red has been phased out at EGCC. $\endgroup$– user14897Jun 8, 2021 at 3:18