Class A - Additional Take-off Procedures — Page 421, Lesson 520

Let’s pick this up right where the logic leads us. We’ve just dealt with the anti-skid system being inoperative, and I want to make sure you understand the why behind the procedure before we ever touch the numbers. Here’s the core problem. When anti-skid is inoperative, the wheels can lock during braking. A locked wheel on a contaminated or wet runway means you lose braking effectiveness — the tyre skids instead of gripping. That directly affects the accelerate-stop distance, which is the distance required to accelerate to V1, then abort the take-off and bring the aeroplane to a complete stop. With less effective braking, that distance grows. It gets longer. Now, the side effect. If you try to fix that by simply reducing the accelerate-stop distance, you might be tempted to lower V1. But lowering V1 has a consequence: it increases the take-off distance. That’s the distance needed to accelerate to V1, suffer an engine failure, and continue the take-off to a safe height. A lower V1 means you commit to the take-off later, so you need more runway to get airborne. So you’re caught between two competing requirements — one wants V1 down, the other wants it up. The resolution is to reduce the mass of the aeroplane. Lower mass decreases both the accelerate-stop distance and the take-off distance required. That way, both remain within the available field lengths — the runway you actually have. So the summary is clean and you should remember it as a pair: with the anti-skid system inoperative, V1 and aeroplane mass must both be decreased. Now, where do you find the actual procedure? It’s detailed on page 34 of section 4 in CAP 698. That’s the Civil Aviation Publication that contains the performance schedules. At the top of that page is a very clear introduction to the procedure, and below that is the method for calculating the mass reduction and the V1 reduction. So the book gives you the logic, and CAP 698 gives you the step-by-step calculation. Let me show you what that looks like in practice. — this is Figure 15.2, the procedure itself. And — Figure 15.3, which shows sample data for a runway with 2 mm contamination. That’s a real-world example of how you’d apply the mass and V1 reduction when the runway isn’t dry. So the takeaway for you as a professional: this isn’t just a memory item. It’s a chain of cause and effect. Anti-skid inoperative → braking degraded → accelerate-stop distance increases → you reduce mass and V1 together to keep both distances within the field. That’s the whole logic in one breath.