MRJT Additional Procedures — Page 120, Lesson 114

I want to walk you through the MRJT Additional Procedures for in-flight diversion with one engine inoperative, using Long Range Cruise, or LRC, performance. This is a critical skill: if you lose an engine en route, you need to know quickly how much fuel you'll burn and how long it will take to reach your alternate airport. The graph we use for this is CAP 697 Figure 4.7.3. It gives you a straightforward method to determine the fuel required and the time for the flight from a diversion point to a selected alternate. Let me be precise about the assumptions built into this graph: it is based upon one engine inoperative and NO pressurization failure. That means the aircraft is not losing cabin pressure—it's just the engine failure. With one engine out, the aircraft will drift down to cruise at its selected level. Drift down means the aircraft gradually descends to an altitude where it can maintain level flight on the remaining engine. Now let's work through Example 6 together, so you see exactly how to use the graph. The scenario: one-engine-inoperative LRC diversion, distance to the alternate is 940 nautical miles, aircraft weight at the point of diversion is 60,000 kg, wind component is 50 knots headwind, cruise flight level is FL260 (that's 26,000 feet pressure altitude), and the ISA deviation is +20°C—so it's 20 degrees warmer than standard. Here's the step-by-step procedure. First, enter the graph with the diversion distance—940 NM. Move vertically upward from that point until you hit the WIND REF LINE. Then, follow the curved flow lines to the value 50 Head—that's your 50-knot headwind. From this position, go vertically upward to the PRESSURE ALTITUDE 1000 ft slope of 26. That slope line represents 26,000 feet. At that intersection, move horizontally to the WEIGHT AT POINT OF DIVERSION REF LINE. Then follow the curved flow lines to intercept the 60,000 kg value. From there, go horizontally to extract the FUEL REQUIRED in kilograms. I'll leave that blank for you to read off the graph. Now, to get the diversion time, we go back. Return to the intersection of the vertical distance/wind line with the PRESSURE ALTITUDE 1000 ft slope of 26. From that same intersection, continue vertically upward to intercept the second PRESSURE ALTITUDE 1000 ft slope of 26. Then move horizontally to the ISA DEV (°C) REF LINE. Follow the temperature slope—in this case +20°C—and read off the time in hours and minutes. There's an important note here: the solid line = 6000 ft, the dashed line = 26,000 ft. So if your cruise level is between those, interpolation is required. For FL260, you use the dashed line. Let's look at Example 7 quickly. Same procedure, different numbers: diversion distance 400 NM, weight 60,000 kg, wind component 100 knots tailwind, cruise FL60 (6,000 feet), ISA deviation +10°C. You'd enter with 400 NM, go to the wind ref line, follow the flow lines to 100 Tail, then up to the pressure altitude slope of 6 (since it's 6,000 feet), across to the weight ref line, follow to 60,000 kg, and read fuel required. For time, you go vertically from the distance/wind/pressure altitude intersection to the second pressure altitude slope, across to ISA deviation, and read time. Now Example 8 adds a twist. It gives you a critical point, or CP, diversion distance of 800 NM, wind component 25 knots head, weight at CP 55,000 kg. But here you're asked for three different calculations. First: fuel required for an engine AND pressurization failure diversion—that's both failures—with outside air temperature at cruise level +5°C and forecast icing. Second: fuel required for a pressurization failure diversion only—same temperature and icing. Third: fuel and time for an LRC engine failure diversion at FL220, with OAT -19°C. Notice the different conditions: the first two involve pressurization failure, which changes the drift-down profile, while the third is just engine failure at a different altitude and temperature. The answers to Examples 6 through 8 are on page 121 of the book, so you can check your work after you practice reading the graph. That's the core procedure: enter with distance, follow wind lines, go to pressure altitude, across to weight, read fuel. Then back to the pressure altitude intersection, up to the second pressure altitude line, across to ISA deviation, read time. Always check whether you're using the solid or dashed line based on your cruise altitude.