Class A - Take-off Climb — Page 433, Lesson 535

We're now into the take-off climb segment of Class A performance, and I want to start with the obstacle limit mass, because that's the practical output of all the obstacle clearance work we've been building. Once you've entered the details of the obstacle — its height and its position relative to the runway — you read the obstacle limit mass straight off the graph. In the example on Figure 16.2, that obstacle limit mass is 51 700 kg. That number is the maximum mass at which you can still guarantee adequate vertical clearance over that obstacle. If you take off heavier than that, you no longer ensure that vertical clearance, so you're not allowed to. But here's the important flexibility: if that obstacle limit mass unduly restricts your take-off mass — meaning it's forcing you to carry less payload than you'd like — you may despatch the aeroplane at a greater mass, provided two conditions hold. First, the aeroplane turns around the obstacle, clearing it by the relevant horizontal margins rather than flying over it. Second, it does not exceed the turn restrictions while trying to do that turn. So the rule gives you a choice: climb over the obstacle with vertical clearance, or turn around it with horizontal clearance — but you must respect whichever constraints apply to the manoeuvre you choose. Now let's move to noise abatement procedures, because these govern how you actually fly the take-off climb in normal operations. The governing principle is that your operating procedures for the take-off climb must maintain the necessary safety of flight operations while minimising exposure to noise on the ground. Safety is never traded away; noise reduction is achieved within that safety envelope. There are two standard procedures, and they differ in one key respect: where the acceleration segment for flap and slat retraction is initiated. NADP 1 is designed to reduce noise for areas very close to the departure end of the runway — that's Figure 16.3. NADP 2 reduces noise for areas more distant from the runway end — that's Figure 16.4. The difference between them is that in one procedure the acceleration segment for flap and slat retraction is initiated before reaching the maximum prescribed height, and in the other it's initiated at the maximum prescribed height. And to get optimum acceleration performance, thrust reduction may be initiated at an intermediate flap setting. Let me walk you through NADP 1 in detail, because it's the one spelled out here. It involves a power reduction at or above a prescribed minimum altitude, and a delay of flap and slat retraction until a prescribed maximum altitude is attained. At that maximum altitude, you accelerate and retract flaps and slats on schedule while maintaining a positive rate of climb, and you complete the transition to normal en route climb speed. There are hard numbers attached to this. The noise abatement procedure is not to be initiated at less than 800 ft above aerodrome elevation. Your initial climbing speed up to the noise abatement initiation point must not be less than V2 plus 20 km/h, which is 10 knots. Once you reach an altitude at or above 800 ft above aerodrome elevation, you adjust and maintain engine power or thrust in accordance with the noise abatement power and thrust schedule provided in the aircraft operating manual. You then maintain a climb speed of V2 plus 20 to 40 km/h — that's 10 to 20 knots — with flaps and slats still in the take-off configuration. Then, at no more than an altitude equivalent to 3000 ft above aerodrome elevation, while maintaining a positive rate of climb, you accelerate and retract flaps and slats on schedule. And at 3000 ft above aerodrome elevation, you accelerate to en route climb speed. So the sequence is: climb at V2 plus 10 to 20 knots with take-off flaps, reduce power at or above 800 ft, hold that configuration until no later than 3000 ft, then clean up and accelerate to en route speed — all while keeping a positive rate of climb throughout. That figure shows the example of a procedure alleviating noise close to the aerodrome — that's NADP 1. The key takeaway is the discipline of the altitudes: 800 ft is your floor for initiating the procedure, and 3000 ft is your ceiling for completing the flap and slat retraction and accelerating.