Aerodromes - Physical Characteristics — Page 377, Lesson 508

I want to walk you through the physical characteristics of an aerodrome — the defined vocabulary that the regulations use to describe every surface, area, and path on the field. This is the language of Air Law, and you need it exact, because every one of these terms carries a specific operational meaning. Let's start with the runway itself. It's defined as a defined rectangular area on a land aerodrome, prepared for the landing and take-off run of aircraft along its length. So it's the paved strip you actually land on and take off from. Now, the strip is different. It's an area of specified dimensions that encloses a runway and taxiway, and its purpose is to provide for the safety of aircraft operations. Think of the strip as the protected envelope around the runway — wider and longer than the pavement itself. From the strip, we get the Runway End Safety Area, or RESA. This is an area defined about the extended runway centre line, adjacent to the end of the strip. Its primary purpose is to reduce the risk of damage to an aeroplane that is undershooting or overrunning the runway. So if an aircraft lands short or goes off the end, the RESA is the forgiving surface that catches it. Next, the shoulder. This is an area adjacent to the edge of a paved surface, prepared to provide a transition between the pavement and the adjacent surface — for aircraft that run off the pavement. It's the graded margin beside the hard surface. Then we have the stopway. This is a defined rectangular area at the end of the take-off run available, prepared and designated as a suitable area in which an aircraft can be stopped in the case of a discontinued take-off. So if you abort the take-off, the stopway is where you can safely stop. Now, the threshold — this is the beginning of that portion of the runway usable for landing. It's the start of the landing surface, and it's not always at the physical start of the pavement. Let's move to the taxiways. A taxiway is a defined path on a land aerodrome, established for the taxiing of aircraft, intended to provide a link between one part of the aerodrome and another. It's how you get from the runway to the apron and back. A rapid exit taxiway, also called a high speed turn-off, is a taxiway connected to a runway at an acute angle. It's designed to allow landing aeroplanes to turn off at higher speeds than on other exit taxiways, thereby minimizing runway occupancy times. So it lets you clear the runway quickly, keeping it free for the next arrival. A taxiway holding position is a designated position at which taxiing aircraft and vehicles may be required to hold, to provide adequate clearance from a runway. You stop there before crossing or entering the runway. A taxiway intersection is simply a junction of two or more taxiways. Now, two more important concepts. The obstacle free zone is a volume of airspace extending upwards and outwards from an inner portion of the strip to specified upper limits, kept clear of all obstructions except for minor specified items. It's a protected volume of air above the strip. A precision approach runway is a runway intended for the operation of aircraft using visual and non-visual aids providing guidance in both pitch and azimuth, adequate for a straight-in approach. These runways are divided into three categories. A take-off runway is a runway equipped to allow take-offs in specified weather minima. Finally, usability — this is the percentage of occasions on which the crosswind component is below a specified value. The usability may be determined for any combination of take-off and landing directions available at an aerodrome. So it tells you how often the wind will allow operations on a given runway direction. That's the full set of physical characteristics. Every one of these terms will come back in the operational rules, so hold onto them precisely.