Let's pick this up right where the definitions leave off — Page 293, Lesson 370

Let's pick this up right where the definitions leave off. We've just established that the take-off is defined by reaching a screen height of 50 ft above the take-off surface, with take-off power set, rotating at \(V_R\), and achieving the specified speed at the screen. Now, two critical speed constraints. First, the rotation speed \(V_R\) must not be less than \(V_{S1}\). \(V_{S1}\) is the stalling speed in a specific configuration — the minimum speed at which the aeroplane is controllable in the air. So you cannot rotate any slower than that; you need to be at or above the stall speed to begin the rotation. Second, the take-off safety speed — that's the screen height speed, the speed you must achieve by the time you reach that 50 ft screen — must not be less than the greater of two values. The first is a speed that is safe under all reasonably expected conditions. The second is \(1.2 \times V_{S1}\). So you take whichever of those two is larger, and that becomes your minimum take-off safety speed. That \(1.2\) factor is your margin above the stall speed to ensure you have adequate control and climb performance at the screen. Now we move into a completely new section: single-engine Class B aircraft take-off. This is a specific category of aeroplane — a small, typically piston-engine aircraft. And here's the key point: there is only one take-off requirement for these aeroplanes. The requirement is that the mass of the aeroplane must be such that the take-off can be completed within the available distances. In other words, the take-off must be complete within the field length available. This single requirement is called the Field Length Requirement. Let me break down the Field Length Requirements. These are detailed in CAP 698, under paragraph 2.1.1, on pages 1 and 2 of section 2. There are two distinct cases. Case 1: No stopway or clearway available. A stopway is an area beyond the runway that can be used for an aborted take-off, and a clearway is an area beyond the runway over which an aeroplane can climb initially. If neither is available, the requirement is that the take-off distance, when multiplied by 1.25, must not exceed the TORA. TORA stands for Take-Off Run Available — the length of runway declared available for the ground run of an aeroplone taking off. So the formula is: Gross TOD × 1.25 must not exceed the TORA. Case 2: A stopway and/or clearway is available. Then you have three separate requirements. First, the take-off distance must not exceed the TORA — so Gross TOD must not exceed the TORA. Second, when multiplied by 1.3, it must not exceed the ASDA. ASDA is the Accelerate-Stop Distance Available — the runway plus stopway length available for an aborted take-off. So Gross TOD × 1.3 must not exceed the ASDA. Third, when multiplied by 1.15, it must not exceed the TODA. TODA is the Take-Off Distance Available — the runway plus clearway length available. So Gross TOD × 1.15 must not exceed the TODA. Let me walk you through an example to make this concrete. Suppose the aeroplane flight manual gives the take-off distance as 3000 ft, and there is no stopway or clearway available at the airport. What is the net take-off distance, or the minimum length of TORA? We use the first requirement: Gross TOD × 1.25 must not exceed the TORA. So we multiply 3000 ft by 1.25, which gives us 3750 ft. Essentially, this means the runway must be at least 3750 ft long — or, more correctly, the Take-Off Run Available (TORA) must be at least 3750 ft long. That's your answer: the minimum TORA is 3750 ft. That figure illustrates the gross take-off distance multiplied by 1.25 must not exceed the TORA. So you can see the relationship visually — the gross take-off distance, scaled up by that 1.25 factor, must fit within the available runway length.