16 145 kg @ 3.04 kg/US.gal — Page 78, Lesson 77

Let’s start with the first line you see: 16 145 kg @ 3.04 kg/US.gal. That’s a fuel load — 16,145 kilograms of fuel, and the density is 3.04 kilograms per US gallon. That’s a standard fuel density figure used in planning unless another value is given. Right below that, under Constants, the book gives you two standard fuel density values: 3.04 kg/US.gal and 6.7 lb/US.gal. So if you ever need to convert between mass and volume of fuel, those are your default numbers. Now, the bullet list defines the key mass terms you’ll use in every flight plan. Let’s go through each one carefully. Maximum Take-off Mass (MTOM) — this is the maximum permissible total aeroplane mass at the start of the take-off run. That means the moment the aircraft begins its take-off roll, its total weight cannot exceed this number. It’s a structural and performance limit. Maximum Landing Mass (MLM) — the maximum total permissible landing mass upon landing under normal circumstances. So when you touch down, the aircraft’s weight must be at or below this value, unless it’s an emergency. Maximum Zero Fuel Mass (MZFM) — the maximum permissible mass of the aeroplane with no usable fuel. This means the weight of the aircraft structure, all equipment, crew, passengers, cargo, and everything else except the fuel that can be burned. It protects the wing structure from excessive bending loads. Dry Operating Mass (DOM) — this is the total mass of the aeroplane ready for a specific type of operation, excluding all usable fuel and traffic load. So it’s the empty-but-ready weight for that particular flight. The book lists what’s included: crew and their baggage, catering and removable passenger service equipment, potable water and lavatory chemicals, and food and beverages. So DOM is the aircraft plus everything that’s needed to operate the flight except the payload and the fuel. Traffic Load — the total mass of passengers, baggage and cargo, including any non-revenue load. So that’s your paying passengers and their bags, plus any freight, and also any staff or company material travelling for free. Then the book gives you a worked example for taxi fuel and APU fuel. The amount of fuel allowed for running the Auxiliary Power Unit (APU), starting the engines, push-back, and taxi to the take-off point is calculated as: Maximum Ramp Mass (MRM) minus Maximum Take-off Mass (MTOM). In the example: 63,060 kg minus 62,800 kg equals 260 kg. That 260 kg is the fuel you’re allowed to burn on the ground before you start the take-off roll. The book also gives you two burn rates: taxi fuel is roughly 11 kg per minute, and the APU burns 115 kg per hour. Next, the maximum traffic load is calculated as MZFM minus DOM. In the example: 51,300 kg minus 34,270 kg equals 17,030 kg. That’s the maximum weight of passengers, bags, and cargo you can carry on that aircraft. Now we move into Optimum Cruise Altitude. The book tells you to refer to CAP 697 Figure 4.1. The optimum pressure altitude for best fuel mileage is presented for two cruise profiles: .78 Mach cruise, and Long Range Cruise (LRC) or .74 Mach. LRC is recommended for minimum trip fuel because it gives 99% of the maximum fuel mileage in zero wind. When you’re cruising within 2,000 feet of the optimum altitude, LRC approximates to a .74 Mach cruise. If you fly above or below that optimum altitude, Table 4.1 tabulates the fuel penalty as a percentage correction. So you can look up how much extra fuel you’ll burn if you can’t fly at the ideal altitude. Then there’s Example 1: you enter the Optimum Cruise Altitude table with a Cruise Mass (Weight) of 56,800 kg, move vertically up to the selected cruise profile — either LRC/.74 Mach or .78 Mach — and then move horizontally to read the optimum cruise pressure altitude. The book leaves blanks for you to fill in from the chart. And there’s an important note: Figure 4.1 has two axes for weight — one is Brake Release Weight (Take-off Weight) and the other is Cruise Weight. Make sure you use the correct one for your calculation.