ATPL GROUND TRAINING SERIES — Page 512, Lesson 603

We're starting a brand-new chapter now — Chapter 38, Engine Instrumentation. And I want to open with the big-picture idea, because it frames everything we're about to do. Just as it would be impossible to fly a large modern aircraft safely without the flight instruments, so would it also be impossible to fly it safely without the engine and aircraft systems instruments. The engine instruments are divided basically into two categories: Performance Indicators or Engine Condition Indicators. Let me define those two categories precisely, because they're the backbone of this whole chapter. Performance Indicators are thrust indicating instruments — the ones that tell you what the engine is actually producing in terms of thrust. The two examples given are the Engine Pressure Ratio gauge, which we'll call EPR, and the Fan Speed gauge, which is the N1 gauge. So when you're looking for "how much thrust am I getting," you're looking at the Performance Indicators. Engine Condition Indicators are a different family. These tell you about the health and state of the engine itself, not directly the thrust output. The examples given are the Exhaust Gas Temperature gauge — EGT — the Compressor Speed, Oil Pressure, and Oil Temperature gauges. So EGT, compressor speed, oil pressure, oil temperature — these are all telling you about the condition of the engine, whether it's running within its limits, whether it's being lubricated properly, whether temperatures are where they should be. Now, one thing I want to make sure you catch: the distinction between the two categories. Performance Indicators answer "what is the engine doing for me right now" — thrust. Engine Condition Indicators answer "is the engine healthy and operating within its limits" — temperature, pressure, speed. Both are essential, but they serve different monitoring purposes. There's a figure here, Figure 38.1, that shows some of the parameters I just mentioned and the position of the sensors that are required to measure them. So the key takeaway from that figure is that every one of these parameters — EPR, N1, EGT, compressor speed, oil pressure, oil temperature — has a physical sensor located somewhere on or in the engine, and that sensor feeds the display in the cockpit. The figure is showing you where those sensors sit. Now, the chapter ahead of us is laid out in a logical order, and I want to give you the roadmap so you know where we're heading. We start with an introduction to the engine instruments, which is where we are now. Then we look at types of display. After that, thrust and power measuring instruments — that's where EPR and torque live. Then engine torque specifically, then engine rpm, then temperature sensing equipment, then pressure gauges, then engine vibration, then the fuel gauge, then remote signal transmission systems, and finally the flight hour meter. So the structure is: first we understand what we're measuring and why, then we go instrument by instrument — torque, rpm, temperature, pressure, vibration, fuel — and then we finish with how the signals get from the sensors to the displays, and the flight hour meter. For now, the core thing to hold onto is this two-category split. Performance Indicators — EPR and N1 — tell you about thrust. Engine Condition Indicators — EGT, compressor speed, oil pressure, oil temperature — tell you about engine health. And every one of those parameters is measured by a sensor at a specific location on the engine, which is what Figure 38.1 is illustrating.