Now, when do you actually need high intensity obstacle lights — Page 447, Lesson 599

Let's pick up right where the material takes us — the high intensity obstacle lights on a tower. I want you to picture a tall tower, and the rule here is about the sequence of flashing. The lights should flash sequentially: first the middle light, second the top light, and last the bottom light. So the order is middle, then top, then bottom — not top-down, not bottom-up, but that specific middle-top-bottom sequence. Now, when do you actually need high intensity obstacle lights? The rule says they should be used to indicate the presence of an object if its height above the level of the surrounding ground exceeds 150 metres, and an aeronautical study indicates such lights to be essential for the recognition of the object by day. So two conditions must both be met: the object is more than 150 metres above the surrounding ground, and a study says the lights are essential for daytime recognition. Next, section 22.12 — Tall Objects. This is about when an object is indicated by low or medium intensity obstacle lights, and the top of the object is more than 45 metres above the level of the surrounding ground — or, if the object is surrounded by buildings, more than 45 metres above the elevation of the tops of those nearby buildings. In that case, additional lights shall be provided at intermediate levels. These intermediate lights must be spaced as equally as practicable between the top lights and ground level — or the level of the tops of nearby buildings, as appropriate — and the spacing must not exceed 45 metres. So the key number here is 45 metres: that's the trigger height, and it's also the maximum allowed spacing between those intermediate lights. Now section 22.13 — Lighting of Aircraft. The lighting of aircraft itself is detailed in Chapter 6, Rules of the Air, and it's covered in the Operational Procedures syllabus. But there's an important point for obstacle marking: aircraft parked on the manoeuvring area are obstacles, and they should be lit either by the aircraft navigation lights or by ancillary lighting — that's anti-collision lighting — which determines the extremities of the aeroplane. So a parked aircraft is treated as an obstacle, and its extremities must be marked. Then section 22.14 — En Route Obstacles. Objects located beyond a 15 km radius of the aerodrome are normally considered obstacles to aircraft in flight only if they exceed 150 metres in height. So beyond 15 km, the threshold is 150 metres. However, prominent objects of less height may be regarded as obstacles if they are on or adjacent to routes regularly used by helicopters. En route obstacles are usually lit by steady red lights at night and high intensity flashing white lights by day. And there's a caveat: environmental considerations may preclude the use of high intensity lights. Section 22.15 — Marking of Overhead Wires or Cables. Overhead wires or cables are marked by coloured spheres. That's the whole rule — coloured spheres on the wires. Now we move to Visual Aids for Denoting Restricted Use Areas, starting with section 22.16 — Closed Runways and Taxiways. A 'closed' marking shall be displayed on a runway or taxiway, or a portion thereof, which is permanently closed to the use of all aircraft. For a temporarily closed runway or taxiway, a closed marking should be displayed — except when the closing is of short duration and adequate warning by air traffic services is provided. So permanent closures always get the marking; temporary ones get it unless it's short and ATS provides adequate warning. On a runway, a closed marking shall be placed at each end of the runway, or portion thereof, declared closed, and additional markings shall be placed so that the maximum interval between markings does not exceed 300 metres. On a taxiway, a closed marking shall be placed at least at each end of the taxiway or portion thereof closed. The colour matters: the marking shall be white when displayed on a runway, and yellow when displayed on a taxiway. There's also a note: when an area is temporarily closed, frangible barriers or markings utilizing materials other than paint, or other suitable means, may be used to identify the closed area. And the excerpt ends mid-sentence on the permanently closed case — that's where we stop for now. Let me show you the relevant figures so you can see these markings and lighting patterns. shows tall objects, and shows the methods of obstacle lighting.