Troubleshooting TFE731 Low Performance
By Craig Bohling
Author's Note: This article is an excerpt from a TFE731 engine troubleshooting class created by Duncan Aviation engine specialists at the request of aircraft operators. The class provides very practical and useful information about how to troubleshoot some of the more common TFE731 discrepancies. The content of the presentation was created by combining years of Duncan troubleshooting experience with the excellent troubleshooting information contained in the Honeywell engine maintenance manuals. The actual class, which covers six TFE731 troubleshooting topics in detail, is presented with audio/visual aids and the support of a Duncan technical panel that offers real life tips and answers to questions. This article will address the topic of troubleshooting low performance problems.
This troubleshooting guide will begin with a typical scenario to help everyone identify with a real world situation. The scenario will be followed by some definitions and background information that are foundational to understanding the detailed steps that will follow. Next, the general troubleshooting logic or 'big picture' will explain how the problem will be approached. This will be followed by some suggested questions for the crew, the actual troubleshooting steps, and finally some technical hints. IMPORTANT: Because of limited space and time, this article will skip over some of the basic maintenance practices used while troubleshooting. It is assumed that the maintenance technician understands proper techniques for preparing the aircraft, applying power, connecting and disconnecting components. As always, the technician should consult the proper approved maintenance manuals for specific steps and information during troubleshooting or any other maintenance work.
Shortly after dispatching the company aircraft for a trip on a warm, summer afternoon, the flight crew returns complaining that the left engine 'temps out' before reaching the target N1 for the day. After some discussion, they admit that the engine has been running warmer than the right side for some time. The crew quickly departs leaving the problem in the hands of the maintenance technician.
Where does the technician start to resolve this problem? What steps need to be taken to get the aircraft back on line?
To get started on troubleshooting this problem, it is important to understand several terms that will be used and some background information.
N1: Fan speed indication. The low-pressure rotor spool speed. The N1 fan speed is an indication of the thrust output of the engine. The pilots reference the N1 fan speed to determine the engine power settings.
Take-off N1 for the day: The N1 setting where the engine produces the required takeoff power for the particular temperature and pressure altitude. This setting is found in the Aircraft Flight Manual.
N2: High-pressure rotor spool speed. This is the speed indication for the power producing, core spool of the engine.
ITT: Interstage turbine temperature. The engine temperature taken between the high-pressure turbine outlet and the low-pressure turbine inlet. (Also known as T5 or temperature station 5.)
P3: High-pressure compressor discharge pressure. This is an air pressure reading taken at the exit of the high-pressure compressor and the entrance of the combustion plenum (at pressure station 3).
P2.3: Low-pressure compressor discharge pressure. This is a pressure reading taken between the low-pressure compressor outlet and the high-pressure compressor inlet. (Also known as pressure station 2.3)
Surge Valve: The surge valve is located between the low-pressure compressor outlet and the high-pressure compressor inlet. The valve modulates open and closed to prevent engine surges and stalls.
Computer mode: This is the normal engine-operating mode when the electronic engine control (EEC) is performing governing, limiting and fuel scheduling functions.
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