AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

How Do Pilots Check That Their Aircraft Engines Are Working Optimally?

As engines are one of the most critical parts of modern airliners, it is crucial that they work optimally. Without an engine, the wings are not capable of generating enough lift to become airborne, the cabin and flight deck would have no electricity, and in a majority of aircraft, there would be no breathable air. Similarly, if the engine is malfunctioning, this can cause a wide range of issues as well.

Pilots must know how the engines are performing at all times. Today, extensive engine performance data is transmitted to the flight deck as well as the airline and engine manufacturer operations centers. As such, if the engine is not working properly, ground teams will know about it almost as soon as the pilots. You may ask yourself: “How is this information displayed for pilots and what does it mean?”

How Jet Engines Work

Before answering this, we must go over how jet engines work. For example, a turbofan engine, like the Rolls-Royce Trent 1000 on the Boeing 787 Dreamliner, goes through four key stages known as “suck, squeeze, bang, and blow.” In this section, we will briefly cover what each stage consists of.

The massive blades at the front of the engine make up the fan which sucks air into the engine. About 90% of this air bypasses the core and exits out of the back of the engine, while the other 10% makes its way through more sets of rotating blades that compress (squeeze) the air, increasing its pressure.

The air then moves into the combustion chamber of the engine, where it is combined with fuel and ignited, causing an explosion (bang) and an increase in heat and energy. From here, the hot air passes (blows) out the back of the engine via rotating turbine blades. Finally, the hot air meets with the cold bypass air, causing an increase in thrust, which drives the aircraft forward.

It is important to note that the compressors and fan at the front of the engine are powered by turbines just downstream of them. To get them moving during the engine start process, they must be powered by either high-pressure air from the auxiliary power unit (APU), or an electrically-powered motor, like the case of the 787. Once the engine is running and self-sustaining, there is no need for additional assistance.

Generally, the thrust produced by the engine is proportional to the quantity of fuel that is injected into the combustion chamber; thus, to increase engine power, the pilots are responsible for pushing the thrust levers forward. This action sends an electrical signal to the engines, thereby increasing the amount of fuel flowing into the combustion chamber. As a result, the speed of the turbine, compressors, and fan increase.

What To Look For

Engines are complex machines that have a number of mechanisms at play within them at one time. That being said, the most important parameters of an engine’s performance are fed to the flight deck, so that pilots can monitor them. In this section, we will outline a few of the most vital.

Turbine Pressure Ratio (TPR)

The Turbine Pressure Ratio (TPR) is the ratio of air pressure exiting the turbine versus the air pressure entering the turbine right after combustion. Often called the “teeper” by pilots, the TPR is how much thrust the engine is generating.


The N1 values are defined as measurements of the speed of a part of the engine, usually displayed as a percentage of the maximum. The N1 stage of the engine includes the front fan and the low-pressure compressor and turbine, which are all connected together with the drive shaft. Because not all aircraft have TPR gauges, operators utilize N1 as a primary indication of engine speed and thrust being produced.

Exhaust Gas Temperature (EGT)

The exhaust gas temperature provides an indication of how hot the air is exiting the rear of the engines, just after the turbines. On some occasions, the EGT on one engine will be hotter than the other because one engine is typically a little older. A higher-than-normal EGT is an indication of an engine surge, stall, failure, or tailpipe fire.

Other Important Parameters to Consider:

  • N2 and N3
  • Fuel Flow
  • Oil Pressure, Temperature, & Quantity
  • Vibration


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