Performance - Introduction — Page 136, Lesson 155

We're starting the Performance section of your ATPL studies, and I want to walk you through the definitions that open this chapter. These aren't just vocabulary—they're the precise, regulatory meanings you'll be tested on and, more importantly, the meanings you'll use operationally. Let's begin with the Fixed Pitch Propeller. This is simply a propeller whose pitch—the angle of the blades—cannot be changed in flight. It's a fixed geometry, as opposed to a variable-pitch or constant-speed propeller. Next, the Flap Extended Speed. This is the highest speed permissible with the wing flaps in a prescribed extended position. Note the word "prescribed"—it's the certified limit for a given flap setting, and exceeding it risks structural damage. Now, Flight Level. This is a surface of constant atmospheric pressure that is related to 1013.25 hPa. It's conventionally the pressure altitude to the nearest 1000 ft, expressed in units of 100 ft. So flight level 250 represents a pressure altitude of 25,000 ft. The key here is that it's based on the standard pressure setting, not the local QNH. Frangibility is a critical safety term. It's the ability of an object to retain its structural integrity and stiffness up to a specified maximum load, but when subjected to a load greater than specified—or struck by an aircraft—it will break, distort, or yield in such a manner as to present minimum hazard to an aircraft. Think of approach lighting masts or runway edge lights: they're designed to fail safely. A Go-around is a procedure involving a decision to abort the landing and climb straight ahead to rejoin the circuit. Such a decision might be taken at any time during the final approach, the transition phase, or even after initial touchdown. So it's not just a missed approach—it covers the whole landing sequence. Gross Height is the true height attained at any point in the take-off flight path using gross climb performance. It's used for calculating pressure altitudes for purposes of obstacle clearance and the height at which wing flap retraction is initiated. This is a planning figure, not an actual measured altitude. Gross Performance is the average performance that a fleet of aeroplanes should achieve if satisfactorily maintained and flown in accordance with the techniques described in the manual. It's the statistical baseline—not the best or worst, but the average. Now, the Ground Minimum Control Speed is a dense one. It's the minimum speed at which the aeroplane can be demonstrated to be controlled on the ground using only the primary flight controls when the most critical engine is suddenly made inoperative and the remaining engines are at take-off thrust. Throttling an opposite engine is not allowed in this demonstration. Forward pressure from the elevators is allowed to hold the nose wheel on the runway; however, nose wheel steering is not allowed. So you're relying purely on rudder and elevator authority. Height is the vertical distance between the lowest part of the aeroplane and the relevant datum. Note the contrast with altitude—height is measured from the aircraft's lowest point, not from the cockpit or the gear. Hydroplaning Speed is the speed at which the wheel is held off the runway by a depth of water and directional control through the wheel is impossible. This is the dynamic aquaplaning threshold where the tyre rides on a water film. The ICAO Standard Atmosphere is defined in ICAO Document 7488/2. For Certification Specifications, the following are acceptable: the air is a perfect dry gas; the temperature at sea level is 15°C; the pressure at sea level is 1013.2 hPa, which is 29.92 in Hg; the temperature gradient from sea level to the altitude at which the temperature becomes –56.5°C is 0.65°C per 100 m, or 1.98°C per 1000 ft; and the density at sea level under the above conditions is 1.2250 kg/m³. These are the fixed constants you'll use for all performance calculations. IFR Conditions are weather conditions below the minimum for flight under visual flight rules. Simple, but operationally defining. Finally, Indicated Airspeed is the speed as shown by the pitot/static airspeed indicator, calibrated to reflect Standard Atmosphere adiabatic compressible flow at MSL—mean sea level—and uncorrected for airspeed system errors. So it's what the instrument reads, before any position or instrument error corrections. That's the full set of definitions opening this performance chapter. Each one is a building block for the take-off, climb, and landing performance calculations we'll be working through.