Performance - Introduction — Page 140, Lesson 165

We're starting the Performance section of your ATPL studies, and the very first thing we have to do is build our vocabulary. Performance is a subject that is absolutely packed with acronyms, and the examiners expect you to know every single one cold. So this first page is essentially a glossary — the alphabet of the subject. Let me walk you through it, because every one of these will come back to haunt you later. Let's start with the landing-related ones. LDA is Landing Distance Available — that's the physical length of runway you actually have to land on, from the threshold to the stop end. LDR is Landing Distance Required — that's the distance your aircraft needs to come to a complete stop, calculated under the regulations. The whole art of landing performance is making sure your LDR never exceeds the LDA. Now, the cruise speed family. LRC is Long Range Cruise speed. MRC is Maximum Range Cruise Speed. And then we have the Mach number versions: MLRC is the Mach Number for Long Range Cruise, and MMR is the Mach of Maximum Range. Don't mix those up — one is a speed in knots, the other is a Mach number. And MMO is the Maximum Operating Mach number — that's the absolute red line you must never exceed in Mach terms. Then we have the mass and environment group. MAT stands for Mass-altitude-temperature — that's the combined effect of your aircraft's mass, the pressure altitude, and the outside air temperature, all of which drive your performance. MTOM is Maximum Take-off Mass, and MZFM is Maximum Zero Fuel Mass — that's the maximum weight of the aircraft with all payload and fuel loaded, but before any usable fuel is added. MSL is simply Mean Sea Level, our reference datum for altitudes. Let's move to the engine and thrust terms. MCT is Maximum Continuous Thrust — the highest thrust you can maintain indefinitely without damaging the engine. N1 is the speed rotation of the fan — that's the low-pressure compressor/fan speed, which is your primary thrust indicator on a turbofan. N-1 means one engine inoperative, and N-2 means two engines inoperative. Note the difference: N1 with no hyphen is fan speed; N-1 with a hyphen is the engine-out condition. OEI also means One Engine Inoperative, and N by itself means all engines operating. Now the fuel and range terms. SFC is Specific Fuel Consumption — that's the fuel flow per unit of thrust per hour, a measure of engine efficiency. SR is Specific Range — the distance you get per unit of fuel. SAR is Specific Air Range — that's the specific range measured through the air, not over the ground. PNR is the Point of No Return — the point in a flight beyond which you no longer have enough fuel to return to your departure point. Let's cover the navigation and airfield terms. PA is Pressure Altitude — the altitude indicated when the altimeter is set to the standard pressure of 1013.2 hPa. QFE is the altimeter subscale setting that causes the altimeter to read zero elevation when you're on the airfield reference point or runway threshold. QNH is the setting that causes the altimeter to read the elevation of the airfield above mean sea level when you're on that same point. And QNE is the indicated height on the altimeter at the aerodrome datum point with the subscale set to 1013.2 hPa. RESA is the Runway End Safety Area — that's the area beyond the runway end designed to stop an aircraft that overruns. PCN is the Pavement Classification Number — that tells you the load-bearing strength of a runway pavement. NOTAM is a Notice to Airmen — a time-critical notice about hazards or changes to facilities. Then we have the operational and system terms. MEL is the Minimum Equipment List — the list of equipment that may be inoperative while still allowing dispatch, provided certain conditions are met. NFP is the Net Flight Path — that's the flight path used for obstacle clearance calculations, which already has the regulatory margins built in. RNP is Required Navigation Performance — a statement of the navigation accuracy required within an airspace. RTO is a Rejected Take-off — an aborted take-off. RZ is Reference Zero. TAS is True Airspeed — your actual speed through the air. TAT is Total Air Temperature — the temperature you'd measure if the air were brought to rest, including the ram rise from your speed. OAT is Outside Air Temperature — the actual free-stream air temperature. MCRIT is the Critical Mach number — the Mach number at which airflow first reaches the speed of sound somewhere on the aircraft. PMC is the Power Management Control — the system that manages engine power. PFD is the Primary Flight Display — your main flight instrument screen. And psi is pounds per square inch, the unit of pressure. That's the full set. I know it's a wall of letters, but this is the foundation — every one of these will appear in the performance charts and questions ahead. Take a breath, and when you're ready, we'll move on to the actual performance concepts.