Let's pick up right where the obstacle identification surface leaves off — Page 438, Lesson 594

Let's pick up right where the obstacle identification surface leaves off. We've just seen that the OIS is a complex plane that starts at the cleared strip and rises in two stages — the inner transition plane climbing to 45 metres over 3000 metres, and the outer transition plane lifting it to 150 metres out to the full 15 kilometres. Now I want to walk you through what happens to the obstacles that protrude through that surface, and then we move into the whole business of marking and lighting them. So, the obstacles that stick up through the OIS are determined by survey. That means someone physically goes out and measures them — they don't guess. And those surveyed obstacles are then detailed in the aerodrome entry in the AIP, the Aeronautical Information Publication. That's the official document where pilots and operators look up the specifics of an aerodrome. So if an obstacle pokes through the OIS within that 15-kilometre radius, it gets recorded in the AIP. Now we shift into Chapter 22, Obstacle Marking and Aerodrome Services. The whole point of marking and lighting obstacles is to reduce hazards to aircraft by indicating their presence. That's the core purpose — you're making the obstacle visible so a pilot doesn't fly into it. Fixed obstacles should be marked, and if the aerodrome is used at night, they should be lit. But here's a nice practical rule: the marking may be omitted when the obstacle is lit by high-intensity obstacle lights by day. So if the lights are bright enough to be seen in daylight, you don't need the paint job. Now let's talk about the movement area. This is the part of the aerodrome used for taxiing, take-off and landing — the runways, taxiways and aprons. Vehicles and other mobile objects on the movement area, excluding aircraft themselves, are considered obstacles. And they shall be marked and, if the vehicles and the aerodrome are used at night or in low visibility, they shall be lit. But there's an exemption: aircraft servicing equipment and vehicles used only on aprons may be exempt. So the fuelling truck that never leaves the apron might not need the full treatment. Also, elevated aeronautical ground lights within the movement area — things like the runway edge lights that stick up — shall be marked so as to be conspicuous by day. They need to be visible in daylight too. Now, how do you actually mark a fixed object? All fixed objects to be marked shall, whenever practicable, be coloured. But if colouring isn't practicable, you display markers or flags on or above them. The colours to use are orange or red — except where those colours merge with the background. Think of a red crane against a red sunset — useless. Against some backgrounds, you may need a different colour from orange or red to get sufficient contrast. So the rule is contrast first, colour second. For vehicles and mobile objects, the colour scheme is different. When a mobile object is marked by colour, you use a single conspicuous colour. Preferably red or yellowish green for emergency vehicles, and yellow for service vehicles. So the fire truck gets red or yellowish green, the maintenance truck gets yellow. And here's an important responsibility point: the aerodrome operator is responsible for ensuring that vehicles on the movement area are lit and/or marked as required — irrespective of ownership. It doesn't matter if the vehicle belongs to an airline or a contractor; the aerodrome operator has to make sure it's compliant. These vehicles include maintenance vehicles, ATC vehicles — air traffic control — 'Follow Me' vehicles, aircraft towing vehicles, refuellers, and so on. And the lights — whenever a permitted vehicle is on the movement area, the lights are to be switched on. Not optional, not when it's dark — always when it's on the movement area. Vehicle obstacle lights are low-intensity flashing yellow. And they're fitted at the highest point of the prime mover — that's the vehicle itself doing the pulling or driving, not the trailer. Trailers, on the other hand, are lit with low-intensity steady red lights at their highest point. So you've got a flashing yellow on the tractor and a steady red on the trailer. And objects with limited mobility — like air bridges, the things that connect the terminal to the aircraft — those are lit with low-intensity steady red lights as well. So the pattern to remember: flashing yellow for the moving vehicle, steady red for trailers and limited-mobility objects. And the whole scheme — marking and lighting — exists for one reason: to indicate the presence of obstacles and reduce the hazard to aircraft.