Class A Aircraft - Take-off — Page 387, Lesson 480

Let's pick up with the take-off safety speed, V2. This is the speed the crew targets when one engine has failed, and it's defined in CAP 698, section 4, page 3, as the target speed to be attained with one engine inoperative. In practical terms, V2 must be reached at or before the screen height — that's the imaginary obstacle height at the end of the take-off distance, typically 35 feet for a Class A aeroplane. Now, why is it called the "safety" speed? There are two speeds that are unsafe to fly near: the stall speed and the minimum control speed. So for V2 to be a safe speed, it must be faster than both of those. But there's a second reason. In the event of an engine failure, V2 must be flown until the aeroplane reaches 400 feet. So the other safe feature is that at V2, the aeroplane can achieve a positive climb. In fact, V2 is the slowest speed that gives sufficient excess thrust to climb above the minimum acceptable climb gradients. There are two constraints on V2. It may not be less than V2MIN — that's the minimum value of V2, a certification limit. And it may not be less than VR plus the speed increment attained up to 35 feet. So V2 is always at least as fast as the rotation speed plus whatever speed is gained between rotation and the screen height. Once the pilots calculate V2, they enter it into the flight management computer, just like V1 and VR. Then V2 is displayed on the speed scale on the left-hand side of the Primary Flight Display, or the Electronic Attitude Director Indicator — the EADI. Now, one more speed: V3. That's the steady initial climb speed with all engines operating. So V3 is the climb speed you use when everything is working normally, as opposed to V2, which is the engine-failure climb speed. Let me also point you to the figures. Figure 14.4 shows V2 as the take-off safety speed. And Figure 14.5 references CAP 698, pages 18 and 19 of section 4, which show how mass, configuration, and density affect V2 — the same way they affect V1 and VR. So you can use those pages to see how each factor changes V2.