In this example the performance limitation is not stated and could be anything — Page 117, Lesson 137

Let’s pick this up right where the worked example left off. In this part of the answer, we’re dealing with the consequences of landing below the Maximum Structural Landing Mass — the MSLM — and then we move into the fuel-jettison and traffic-load calculations. First, the performance limitation. In this example, the performance limitation is not stated, and it could be anything — a runway length restriction, a sloping runway, an obstruction limitation, and/or altitude and temperature limitations. So the point is, we don’t know exactly what’s limiting the landing performance here; it’s just some constraint that forces the landing mass down. Now, what happens if the aeroplane lands below the MSLM but still has to stop hard? The aeroplane might sustain a burst tyre, brake fade, and/or brake fire as a result of heavy braking. Tyre temperatures might exceed limits and delay the take-off time even if they do not burst. So even if the tyre doesn’t blow, the heat can still cause a delay. The climb slope for obstacle clearance during a go-around might be reduced — that’s because a go-around from a heavy landing configuration may not have the same climb gradient. But here’s the key structural point: as the landing is below the MSLM, the structure itself should not suffer direct damage, providing the aeroplane comes to a stop without hitting anything. So the structure is safe as long as you don’t collide with something. Now, question 22, answer b. The pilot calculates the amount of fuel to jettison to reduce the mass to a safe level at or below the RLM — the Regulatory Landing Mass. Before jettisoning the fuel, the pilot should attempt to declare an emergency if time permits, and advise Air Traffic Control of his intentions. So the fuel jettison is a deliberate act to get the mass down to a safe landing value, and you coordinate it with ATC. Now, question 23, answer a. This is the big worked example, and the golden rule here is to work out the fuel states first. Once the fuel states are known, you can simply use the three formulae to determine the answer. Let’s lay out the given values. TOF — that’s the Take-Off Fuel — equals 9700 plus 1200 plus 1400, which gives 12,300. FR — the Fuel Reserve — equals 1200 plus 1400, which gives 2600. DOM is the Dry Operating Mass, 34,900. MZFM is the Maximum Zero Fuel Mass, 53,000. RTOM is the Regulated Take-Off Mass, 62,800. And RLM is the Regulatory Landing Mass, 54,900. Now the three formulae. Formula 1: MZFM minus DOM equals 53,000 minus 34,900, which is 18,100. Formula 2: RTOM minus DOM minus TOF equals 62,800 minus 34,900 minus 12,300, which is 15,600. Formula 3: RLM minus DOM minus FR equals 54,900 minus 34,900 minus 2,600, which is 17,480. The allowable Traffic Load — the TL — is the lowest of these three values. So we take the lowest of 18,100, 15,600, and 17,480, which is 15,600 kg. That’s the maximum traffic load the aeroplane can carry under these constraints. Now the actual traffic load. Actual TL equals passengers plus baggage. Here we have 130 passengers at 84 kg each, plus 130 pieces of baggage at 14 kg each. So that’s (130 × 84) plus (130 × 14), which gives 12,740 kg. The difference between the allowable TL and the actual TL is the underload. And the cargo that can be taken is exactly that underload. So cargo equals 15,600 minus 12,740, which is 2,860 kg. That’s the amount of cargo you can add on top of the passengers and their baggage without exceeding the allowable traffic load. So the whole logic here: work out fuel states first, then apply the three limiting formulae, take the lowest as your allowable traffic load, subtract what you already have on board, and the remainder is the cargo you can still carry.