Performance - Introduction — Page 136, Lesson 159

We're starting the Performance section of your ATPL studies, and I want to walk you through the core definitions that everything else will build on. These are the exact terms you'll see in the exam and in the manuals, so I'll give you the precise professional meaning for each one, then explain what it actually means in practice. Let's begin with the Missed Approach. This is when an aircraft is caused to abort a landing after it has already started its landing approach. The aircraft then has to follow a set missed approach procedure to leave the airspace surrounding the terminal. So it's not just "going around" — it's a defined, published procedure to get you safely out of the terminal area and reposition for another attempt or a diversion. Next, Net Height. This is the true height attained at any point in the take-off flight path using net climb performance. Net height is used to determine the net flight path that must clear all obstacles by the statutory minimum to comply with the Operating Regulations. So when we talk about obstacle clearance on departure, we're not using the raw climb performance — we're using this reduced, "net" figure. That leads directly into Net Performance. Net performance is the gross performance diminished to allow for various contingencies that cannot be accounted for operationally — for example, variations in piloting technique, temporary below-average performance, and so on. It is improbable that the net performance will not be achieved in operation, provided the aeroplane is flown in accordance with the recommended techniques. So think of it this way: gross performance is what the aircraft is theoretically capable of; net performance is the conservative, guaranteed figure you can rely on for certification and obstacle clearance. Now, Outside Air Temperature — this is simply the free air static, or ambient, temperature. That's the temperature of the air outside the aircraft, not affected by the aircraft's own heat or compression. Moving to the propeller, we have Pitch Setting. This is the propeller blade setting determined by the blade angle, measured in a manner and at a radius declared by the manufacturer and specified in the appropriate Engine Manual. So it's not just "the angle of the blades" — it's a specific, manufacturer-defined measurement at a specific point on the blade. Now, careful here — Pitch is a different term. Pitch is the motion of the aeroplane about its lateral axis. That's the nose-up or nose-down rotation. So "pitch setting" is about the propeller blade angle, while "pitch" alone is the aircraft's attitude motion. Don't confuse the two. Next, the Pitot Tube. This is a small tube whose open end collects Total Pressure. That's the pressure you get when the airflow is brought to rest — it's the sum of static pressure and dynamic pressure. This is what feeds your airspeed indicator. Pressure Altitude is the altitude of an aircraft above the pressure level of 1013.25 hPa. This is achieved by setting the altimeter subscale to 1013 hPa and reading the altitude indicated. So when you set your altimeter to the standard setting of 1013.25 hectopascals, the reading you get is pressure altitude — it's independent of the actual local pressure. Reference Landing Speed is the speed of the aeroplane, in a specified landing configuration, at the point where it descends through the landing screen height in the determination of the landing distance for manual landings. So it's a specific speed, in a specific configuration, at a specific point in the landing profile — used to calculate landing distance. Rejected Take-off, or RTO, is a situation or event in which it is decided, for safety reasons, to abandon the take-off of an aircraft. This is the decision to stop the take-off run rather than continue. Roll is the motion of the aeroplane about its longitudinal axis — that's the wing-tip up or down rotation. Rotation Speed is the speed at which, during the take-off, rotation is initiated with the intention of becoming airborne. That's the speed at which you pull back on the controls to raise the nose and lift off. Runway is a defined rectangular area on a land aerodrome prepared for the landing and take-off run of aircraft along its length. Simple enough — the paved strip itself. Runway Strip is an area of specified dimensions enclosing a runway intended to reduce the risk of damage to an aircraft running off the runway and to protect aircraft flying over it when taking off or landing. So it's the wider, cleared area around the runway — it's there for safety, both for aircraft that veer off and for aircraft flying low over it. Runway Threshold is the beginning of that portion of the runway usable for landing. That's the start of the landing portion — where you aim to touch down just beyond. Now, the Screen is an imaginary barrier, located at the end of the Take-off Distance Available, or TODA, or the beginning of the Landing Distance Available, or LDA. The screen is of no operational significance, but the test pilots use the height of the screen when assessing the performance of the aeroplane. So it's a notional obstacle used for certification — you must clear it by a certain height, but you never actually see it. Finally, Service Ceiling is the pressure altitude at which the rate of climb is reduced to a specified minimum value — approximately 300 feet per minute. So that's the altitude above which you can no longer maintain that minimum climb rate. Let me show you the runway-related concepts visually, because the clearway and stopway definitions build on this. shows how clearways extend from the end of the runway with an upward slope not exceeding 1.25%. shows stopways, which are able to support the aeroplane during a rejected take-off and are marked by large yellow markings. And illustrates both stopways and clearways together at an aerodrome. So to tie it together: the runway is where you operate, the strip protects you around it, the threshold is where landing begins, and the screen is the imaginary obstacle you must clear. Net performance is your guaranteed climb capability, and net height is what you use to prove obstacle clearance. These are the building blocks for all the take-off and landing performance calculations we'll do next.