Outboard means the side farthest from the taxiway — Page 405, Lesson 557

Let’s pick this up right where the markings leave off and move into the signs themselves. We’ve already covered the painted markings on the pavement — now we’re talking about the physical signs that stand beside the taxiway, because those signs carry the information that the paint alone can’t always give you. First, the big rule that ties signs to markings: a runway designation sign at a taxiway/runway intersection should be supplemented with a category I, II or III holding position sign. So if you’re holding short of a runway at a point that protects an ILS or MLS critical area — that’s the sensitive zone where the guidance signal can be disturbed — you get the painted holding position marking on the ground, and next to it a sign that tells you which category of holding position it is. Category I, II or III refers to the precision approach category, and the sign tells you which one you’re protecting. Now, at a taxiway/runway intersection, the runway designation sign — the one that tells you which runway you’re about to cross or enter — should be supplemented with a location sign in the outboard position. Outboard means the side farthest from the taxiway. So you have the runway designation sign, and beyond it, further away from the taxiway, a location sign that tells you where you are. And if entry into an area is prohibited, a NO ENTRY sign shall be provided. That’s a mandatory sign — it’s not optional. Now let’s talk about where these signs actually go, because placement is a safety-critical detail. The general principle is that signs are located so that pilots or vehicle drivers can see them, and they must never be positioned so as to create a hazard to aircraft. So visibility first, obstruction never. Here’s the specific placement for each sign. A runway designation sign at a taxiway/runway intersection shall be located at least on the left side of the taxiway, facing the direction of approach to the runway. Where practicable, you put one on each side. So the minimum is left side, and if you can, both sides. A NO ENTRY sign shall be located at the beginning of the area to which entrance is prohibited, at least on the left hand side of the taxiway as viewed by the pilot. Again, where practicable, on each side. So the NO ENTRY sign marks the very start of the prohibited area, and it’s on your left as you approach. A Category I, II or III holding position sign shall be located on each side of the holding position marking, facing the direction of approach to the critical area. Note that one — for the category holding position sign, the standard is both sides, not just the left. And finally, a taxi-holding position sign is to be located on the left side of the taxi-holding position, facing the approach to the runway or the ILS/MLS critical or sensitive area, as appropriate, and where practicable, on each side. So the taxi-holding position sign — the one that marks where you stop before the runway — faces you as you approach the runway or the critical/sensitive area, and the minimum is left side, both sides if possible. So the pattern you should see here: left side is the minimum everywhere, both sides is the preferred standard where practicable, and the category I/II/III holding position sign is the one that’s required on both sides. The signs face the direction of approach — they’re meant to be read by the pilot coming toward them, not by someone looking back. And every sign placement is chosen so the pilot can see it without the sign ever becoming a hazard to the aircraft. That’s the full picture on sign locations. The key takeaway: signs supplement the markings, they’re placed for visibility on the approach side, left side minimum, both sides preferred, and the category holding position sign is the one that must be on both sides.