Multi-engine Class B - Take-off — Page 341, Lesson 423

Right, let's get into the take-off requirements for a Multi-engine Class B aeroplane. This is where we start locking in some very specific speeds and obstacle clearance rules. First, the speeds. We have the rotation speed, which we call VR. The rules state that VR must not be less than two values: it must not be less than 1.05 times VMC, and it must not be less than 1.1 times VS1. Let me define those for you. VMC is the minimum control speed — the lowest speed at which the aeroplane can still be controlled in the air with the critical engine failed. VS1 is the stalling speed in a specific configuration. So rotation must be comfortably above both of those. Then we have the take-off safety speed, which is the speed at 50 feet. That speed must not be less than three things: a speed that is safe under all reasonably expected conditions, 1.1 times VMC, and 1.2 times VS1. And there's one more constraint: VMC for take-off must not exceed 1.2 times VS1. Now, an important note for your exam preparation: these speeds are not found in CAP 698. CAP 698 is the CAA document with the performance data tables. So these particular speed relationships must be committed to memory — you won't be able to look them up. Next, the obstacle clearance requirements, which come from EU-OPS 1.535. For a Multi-engine Class B aircraft, you must demonstrate clearance of obstacles after take-off up to a height of 1500 feet. Unlike the speeds, all the obstacle clearance requirements are found in CAP 698, so you don't need to memorise them — you can find them all on page 9 of section 3. But let's look at the actual clearance margins. Obstacles must be cleared by either a vertical margin of at least 50 feet, or a horizontal distance of at least 90 metres plus 0.125 times D, where D is the distance from the end of the TODA — that's the take-off distance available — or the end of the TOD if a turn is scheduled before the end of the TODA. For aeroplanes with a wingspan of less than 60 metres, the horizontal distance may be taken as 60 metres plus half the wingspan plus 0.125 times D. Now, the conditions that must be assumed when demonstrating this obstacle clearance. First, the flight path begins at a height of 50 feet above the surface at the end of the TODR — the take-off distance required — and ends at a height of 1500 feet above the surface. Second, the aeroplane is not banked before it has reached 50 feet, and thereafter the angle of bank does not exceed 15 degrees. Third, failure of the critical engine occurs at the point on the all-engine take-off flight path where visual reference for the purpose of avoiding obstacles is expected to be lost. Fourth, the gradient to be assumed from 50 feet to the point of engine failure is equal to the average all-engine gradient during climb and transition to the en-route configuration, multiplied by a factor of 0.77. And finally, the gradient from the point of engine failure to 1500 feet is equal to the one-engine-inoperative en-route gradient. So the picture is: you accelerate, rotate at VR, climb to 50 feet, and from there you have a defined flight path up to 1500 feet that must clear obstacles by that vertical or horizontal margin, assuming the critical engine fails at the worst point and you're not banking more than 15 degrees. That's the core of the Class B take-off obstacle clearance.