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

I want to walk you through the Class A take-off climb, and we're going to finish the obstacle limit mass story and then move into noise abatement procedures. First, let's close out the obstacle limit mass. When you've entered the obstacle details onto the graph, as the example shows, you read off the obstacle limit mass. In the example on the graph itself, that value is 51 700 kg. Taking off with a mass higher than that would not ensure adequate vertical clearance — that's the whole point of the limit. But here's the important operational twist: if that mass unduly restricts your take-off mass, you may still despatch the aeroplane with a greater mass, provided two conditions hold. First, the aeroplane turns around the obstacle, clearing it by the relevant horizontal margins. Second, it does not exceed the turn restrictions while trying to do so. So the obstacle limit mass is a vertical clearance limit, and you can trade vertical clearance for horizontal clearance by turning around the obstacle — but only within the turn restrictions. Now let's move to noise abatement procedures. The governing principle is that aeroplane operating procedures for the take-off climb shall ensure the necessary safety of flight operations is maintained whilst minimising exposure to noise on the ground. So safety stays paramount; noise reduction is what we optimise within that safety envelope. There are two procedures. The first is NADP 1 — that's Noise Abatement Departure Procedure 1. It's intended to provide noise reduction for noise-sensitive areas in close proximity to the departure end of the runway. The second is NADP 2, which provides noise reduction to areas more distant from the runway end. The two procedures differ in one key respect: the acceleration segment for flap and slat retraction is either initiated prior to reaching the maximum prescribed height, or at the maximum prescribed height. And to ensure optimum acceleration performance, thrust reduction may be initiated at an intermediate flap setting. Let's look at NADP 1 in detail, because that's the procedure spelled out in this excerpt. It involves a power reduction at or above the prescribed minimum altitude, and the delay of flap and slat retraction until the prescribed maximum altitude is attained. At that prescribed maximum altitude, you accelerate and retract flaps and slats on schedule whilst maintaining a positive rate of climb, and you complete the transition to normal en route climb speed. Now the specific numbers. The noise abatement procedure is not to be initiated at less than 800 ft above aerodrome elevation. The initial climbing speed to the noise abatement initiation point shall not be less than V2 plus 20 km/h, which is 10 kt. V2, remember, is the take-off safety speed. On reaching an altitude at or above 800 ft above aerodrome elevation, you adjust and maintain engine power and thrust in accordance with the noise abatement power and thrust schedule provided in the aircraft operating manual. You maintain a climb speed of V2 plus 20 to 40 km/h — that's 10 to 20 kt — with flaps and slats in the take-off configuration. Then, at no more than an altitude equivalent to 3000 ft above aerodrome elevation, whilst maintaining a positive rate of climb, you accelerate and retract flaps and slats on schedule. At 3000 ft above aerodrome elevation, you accelerate to en route climb speed. So the sequence for NADP 1 is: climb at V2 plus 10 kt minimum, no power reduction below 800 ft, then at or above 800 ft reduce power per the manual's schedule, keep climbing with flaps and slats in take-off configuration at V2 plus 10 to 20 kt, and no later than 3000 ft accelerate and retract the flaps and slats, then accelerate to en route climb speed. The figure shows this as an example of a procedure alleviating noise close to the aerodrome — that's NADP 1. One thing to keep straight: the 800 ft and 3000 ft are both referenced to aerodrome elevation, not to the runway surface or to your altitude above the ground at any given moment. And the speed band V2 plus 10 to 20 kt is your target through the noise abatement climb segment. That's the core of NADP 1.