Medium Range Jet Transport (MRJT) Simplified Flight Planning — Page 85, Lesson 82

I want to walk you through the additional allowances that apply when you're doing simplified flight planning for a Medium Range Jet Transport — the MRJT. These are the extra fuel and time adjustments you need to account for when your flight doesn't follow the standard Long Range Cruise profile exactly. Let's start with the Cost Index Adjustment. The Long Range Cruise, or LRC, Simplified Flight Planning charts are built around climb, cruise, and descent speeds that give you an approximate minimum trip fuel. That means the baseline numbers on those charts assume you're flying for best fuel economy. But if you plan to operate the flight with the Flight Management System — the FMS — in the economy mode, or ECON mode, the flight profile changes. The FMS will choose different speeds based on the cost index you enter, which trades off fuel cost against time cost. So you need adjustments to both the trip fuel and the trip time to account for that different profile. The table above the text itemizes exactly what those adjustments are — you'd look up the specific values from that table when you're doing your planning. Now let's move to Ground Operations. There are two key fuel-saving considerations here. First, you can save fuel by minimizing APU operation — that's the Auxiliary Power Unit, the small turbine engine in the tail that provides electrical power and air conditioning on the ground. The average APU fuel flow for normal operations is 115 kilograms per hour, or 250 pounds per hour. That's a significant burn, so you want to run the APU only as long as necessary. Second, the taxi fuel allowance is 11 kilograms per minute, or 25 pounds per minute. That's the fuel you plan to burn while taxiing from the gate to the runway. You multiply that rate by your expected taxi time to get the taxi fuel figure for your flight plan. Finally, we have adjustments for Cruise conditions involving the Air Conditioning Packs and Engine/Wing Anti-ice. These are systems that increase engine workload and therefore fuel consumption. If the AC packs — the air conditioning packs — are set to high flow, you need to increase the trip fuel by 1%. High flow is typically used when you need more cabin ventilation or cooling, and it draws more bleed air from the engines. For anti-ice, there are two levels. If you're using engine-only anti-ice, you increase the trip fuel by 70 kilograms per hour. That's the additional fuel burn per hour of flight time while the engine anti-ice system is operating. The text doesn't specify the wing anti-ice figure here, but the principle is the same — any anti-ice system that uses engine bleed air increases fuel flow. So to summarise: when you're doing simplified flight planning for the MRJT, you start with the LRC chart numbers, then you layer on these adjustments — the cost index adjustment if you're using ECON mode, the APU and taxi fuel for ground operations, and the AC pack and anti-ice increments for cruise. Each one is a specific, quantifiable addition to your fuel and time calculations.