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

Let’s pick up with the take-off speeds for a Class A aeroplane, and I want to focus on V2, the take-off safety speed. V2 is defined as the take-off safety speed. In CAP 698, Section 4, page 3, it states that V2 is the target speed to be attained with one engine inoperative. That means V2 must be reached at or prior to the screen height — the screen height being the imaginary obstacle height you must clear at the end of the take-off distance. So the aeroplane must be at V2 by the time it reaches that screen. Now, why is V2 called the safety speed? What is actually safe about reaching it? There are two main speeds which, when you fly close to them, may be unsafe. The first is the stall speed, and the second is the minimum control speed. So for V2 to be called a safe speed, it must be faster than both of those. That is the first reason. There is a second reason. In the event of an engine failure, V2 must be flown until the aeroplane reaches 400 ft. So the other safe feature about V2 is that the aeroplane is able to achieve a positive climb. In fact, V2 is the slowest speed which will enable the aeroplane to have sufficient excess thrust to climb above the minimum acceptable climb gradients. So V2 is not just about staying above stall and above minimum control speed — it is also the speed that guarantees you have enough excess thrust to meet the required climb gradient after an engine failure. Now, V2 may not be less than two things. First, it may not be less than V2MIN — that is the minimum value of V2, the lowest speed that satisfies the safety criteria. Second, it may not be less than VR plus the speed increment attained up to 35 ft. In other words, from the rotation speed VR, the aeroplane accelerates during the climb to the screen, and V2 must be at least as high as the speed you actually reach by the time you get to 35 ft. Now, just like V1 and VR, V2 is affected by mass, configuration, and density. In CAP 698, Section 4, pages 18 and 19, you can see how these factors change V2. So ensure you can use those pages to see for yourself how mass, configuration, and density each affect V2. Once V2 is calculated by the pilots, it can be entered into the flight management computer, just like V1 and VR were. Having done that, V2 will be displayed to the pilots in the speed scale on the left-hand side of the Primary Flight Display, or the Electronic Attitude Director Indicator — the EADI. Now, there is one more speed introduced here: V3. V3 is the steady initial climb speed with all engines operating. So while V2 is the target speed with one engine inoperative, V3 is the speed you use for the initial climb when all engines are running normally. So to summarise the key points: V2 is the take-off safety speed, it must be reached at or before the screen height, it must be faster than stall speed and minimum control speed, it must allow a positive climb with sufficient excess thrust to meet the minimum climb gradients, and it may not be less than V2MIN or less than VR plus the speed increment attained up to 35 ft. And V3 is the steady initial climb speed with all engines operating.