Medium Range Jet Transport (MRJT) Simplified Flight Planning — Page 78, Lesson 80

I want to walk you through the next part of the MRJT Simplified Flight Planning chapter. We're going to look at how to determine the optimum cruise altitude for a given weight and Mach number, and then we'll move into the concept of short distance cruise altitude and the simplified flight planning graphs. Let's start with Example 2. Here we have a cruise weight of 62,000 kg. The task is to calculate the optimum pressure altitude for a 0.74 Mach cruise. Then, we also need to find the fuel and mileage penalty if the aircraft is cleared to fly 4,000 feet below that optimum altitude. The answer is on page 80 of the book. The key point here is that the optimum altitude is the one that gives the best fuel economy for that weight and Mach number. If you're forced to fly lower, you'll burn more fuel and cover less distance per unit of fuel — that's the penalty. Now, let's talk about Short Distance Cruise Altitude. This is a specific concept for sectors of 235 NM or less. For such short sectors, the cruise distance is limited by the distances required for the climb and the descent. In other words, you spend a significant portion of the flight just getting up and coming back down, so the actual cruise segment is very short. The Short Distance Cruise Pressure Altitude table — which you'll find in CAP 697 Figure 4.2 — shows the maximum pressure altitude at which it is possible to cruise for at least one minute. That's the definition: the highest altitude you can reach and still have at least 60 seconds of level cruise before you have to start descending. There's an important note here: the only interpolation for ISA is done between +10°C and +20°C. That means when you enter the table, you only need to interpolate between those two temperature deviations from the International Standard Atmosphere. For any other ISA deviation, you just use the nearest value. Let's walk through Example 3. We enter the table with the trip distance — here it's 175 NM. Then we move to the temperature line, which is ISA +20°C. From there, we move horizontally to the Reference Line. Then we follow the trade lines — those are the curved guide lines — to intercept the vertical line at the Brake Release Weight, which is 52,000 kg. Once we hit that intercept, we move horizontally to read the optimum cruise pressure altitude. The answer is on page 80. Now Example 4. Here the sector distance is 150 NM, the temperature at Mean Sea Level take-off is 30°C, and the brake release weight is 42,500 kg. We need to calculate the maximum short distance cruise pressure altitude. Again, the answer is on page 80. Now we move on to Simplified Flight Planning - Introduction. These are graphs provided in the CAP 697 MRJT1, specifically Figures 4.3.1a through 4.4. They cover different cruise modes and distance ranges. For Long Range Cruise, there are three graphs: one for 100 to 600 NM, one for 200 to 1,200 NM, and one for 1,000 to 3,000 NM. For 0.74 Mach Cruise, there are also three graphs covering the same distance ranges: 100 to 600, 200 to 1,200, and 1,000 to 3,000 NM. For 0.78 Mach Cruise, again three graphs with the same three distance ranges. And finally, there is one graph for 300 KIAS Cruise — that's 300 knots indicated airspeed. These graphs allow you to quickly plan a flight without doing detailed calculations for every segment. You enter with the distance, weight, and temperature, and you can read off fuel, time, and altitude information directly. We'll work through how to use each one as we go.