Performance - Introduction — Page 130, Lesson 153

We're starting the Performance section of your ATPL studies, and I want to walk you through the very first thing you'll need: the definitions. This is the foundation—every performance calculation, every take-off decision, every limit you'll compute later hangs on these exact terms. So let's take them in order. First, we have Continuous One Engine Inoperative Power and Continuous One Engine Inoperative Thrust. These are two separate definitions, but they're twins. The power version is the power 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. The thrust version is exactly the same idea, but for thrust. So the key phrase is "periods of unrestricted duration"—that means this is the setting you can use indefinitely, not just for a short burst. After an engine fails, you need a power or thrust setting you can hold for the rest of the flight, and that's what this defines. Next, the Critical Engine. This is the engine whose failure would most adversely affect the performance or handling qualities of an aircraft. Think of it as the worst-case engine to lose. On a multi-engine aircraft, they're not all equal—losing one particular engine might create more yaw, more drag, or worse control. That's the critical one, and it's the one we plan around for all our engine-failure calculations. Then we have 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 middle ground—there's moisture, 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 dry runway isn't just "no water"—it can actually have moisture, as long as the surface is engineered to keep braking effective. That's an important distinction for your performance calculations. Next, 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 authority officially publishes these numbers, and they're the legal basis for your take-off and landing performance calculations. Now, the big one—Decision Speed, which is V1. This has two parts, and you need both. First, it's the maximum speed in the take-off at which the pilot can take the first action—for example, apply brakes, reduce thrust, deploy speed brakes—to stop the aeroplane within the accelerate-stop distance. Second, it's also 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 balance: below it, you stop; above it, you go. And note that VEF is the engine failure speed—the speed at which the critical engine is assumed to fail in your calculations. Let me show you this graphically. Here's Figure 14.1, a graph showing the ideal position of V1. You can see that a V1 at the intersection point of the graph is the ideal—that's where the accelerate-stop distance and the take-off distance balance perfectly. Then we have Density Altitude. This is the altitude in ISA, where the prevailing measured density occurs. So it's not your actual altitude—it's the altitude in the International Standard Atmosphere that corresponds to the air density you're actually experiencing. Hot days and high pressure altitudes make your density altitude higher, which degrades performance. Next, Drag. This is that force on an aeroplane which directly opposes thrust. Simple, but fundamental—thrust pushes forward, drag pushes back. Then Elevation. This is the vertical distance of an object above mean sea level. It may be given in metres or feet. So that's your airport's elevation, the height of the terrain above sea level. Now, En Route. This defines a phase of flight. The en route phase 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 starts at 1500 feet above where you took off, and it ends at either 1000 or 1500 feet above where you'll land, depending on your aircraft class. Class A is your larger transport category aircraft; Class B is smaller. Next, Equivalent Airspeed, or EAS. This 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 high speeds and high altitudes, the air compresses around the aircraft, and your airspeed indicator reads differently. EAS corrects for that. In a standard atmosphere, EAS equals CAS. Then Exhaust Gas Temperature, or EGT. This is the average temperature of the exhaust gas stream. Simple—it's a measure of how hot the gases are leaving the engine, and it's a key engine monitoring parameter. 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 of the aeroplane in segment four of the take-off flight path with one engine inoperative. They're identical definitions, just different names. 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 show you the relationship of V1 with VMCG and VMBE. Here's Figure 14.2. V1 cannot be allowed to be less than VMCG because engine failure below VMCG means the aircraft can't be controlled on the ground. And here's V2, the take-off safety speed. That's Figure 14.4. So those are your foundational definitions. Every one of these terms will come back in your performance calculations, so make sure you know them cold.