Performance - Introduction — Page 130, Lesson 153

We're starting a new section now: Performance — Introduction. This is the glossary of definitions that underpins the whole performance syllabus, so I want to walk you through each term carefully, because these exact definitions are what you'll be tested on and, more importantly, what you'll be operating to. Let's begin with the power and thrust definitions. We have Continuous One Engine Inoperative Power and Continuous One Engine Inoperative Thrust. These are the power, or thrust, identified in the performance data for use after take-off when a power unit has failed or been shut down, during periods of unrestricted duration. So the key idea here is that this is the setting you can use indefinitely — not a temporary rating. It's the sustainable output after an engine failure. Next, the Critical Engine. This is the engine whose failure would most adversely affect the performance or handling qualities of an aircraft. In other words, if you lose this particular engine, the situation is worse than if you lost any other one. That's the one we plan around. Now let's look at runway conditions. A Damp Runway is considered damp when the surface is not dry, but when the moisture on it does not give it a shiny appearance. So it's a subtle distinction — moisture is present, but not enough to reflect light. A Dry Runway is one which is neither wet nor contaminated, and includes those paved runways which have been specially prepared with grooves or porous pavement and maintained to retain 'effectively dry' braking action even when moisture is present. So a grooved runway can still be considered dry for performance purposes, because the grooves maintain braking effectiveness. Then we have the Declared Distances — these are the distances declared by the aerodrome authority for the purpose of application of the requirements of the Air Navigation Order. So the airport publishes these, and we use them for our take-off and landing calculations. Now, the Decision Speed, V1. This is a critical one. It's the maximum speed in the take-off at which the pilot can take the first action — for example, apply brakes, reduce thrust, or deploy speed brakes — to stop the aeroplane within the accelerate-stop distance. It also means the minimum speed in the take-off, following a failure of the critical engine at VEF, at which the pilot can continue the take-off and achieve the required height above the take-off surface within the take-off distance. So V1 is a dual-purpose speed: below it, you can stop; above it, you must continue. Let me show you the graph of the ideal position of V1. You can see from the graph that V1 sits at the intersection point — balancing the distance needed to stop against the distance needed to continue. Density Altitude is the altitude in ISA, the International Standard Atmosphere, where the prevailing measured density occurs. So it's a way of expressing the actual air density in terms of a standard altitude. Drag is that force on an aeroplane which directly opposes thrust. Simple but fundamental. Elevation is the vertical distance of an object above mean sea level. This may be given in metres or feet. Now, the En Route phase. This extends from 1500 ft above the take-off surface level to 1000 ft above the landing aerodrome surface level for Class B aeroplanes, or to 1500 ft above the landing aerodrome surface level for Class A aeroplanes. So the en route segment is defined differently depending on the aircraft class. Equivalent Airspeed is the calibrated airspeed corrected for compressibility at the particular pressure altitude under consideration. It is equal to Calibrated Airspeed in a Standard Atmosphere. So at standard conditions, EAS and CAS are the same. Exhaust Gas Temperature is the average temperature of the exhaust gas stream. That's your EGT. Finally, we have three related speeds. Final En Route Climb Speed is the speed of the aeroplane in segment four of the take-off flight path with one engine inoperative. Final Segment Speed is the same thing — the speed in segment four of the take-off flight path with one engine inoperative. And Final Take-off Speed is the speed of the aeroplane that exists at the end of the take-off path in the en route configuration with one engine inoperative. Let me also show you the relationship of V1 with VMCG and VMBE. V1 cannot be allowed to be less than VMCG, because engine failure below VMCG means the aeroplane cannot be controlled on the ground. So those are the core definitions we're starting with. Each one of these will come back in the detailed performance calculations, so it's worth getting them firmly in your mind now.