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Low rpm, EGT, and fuel flow at expected EPR

Aviation Mechanic Powerplant (AMP) practice question 4 of 13 on Turbine Engines. ACS element AM.III.B.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONDuring a run-up, a turbofan engine set to its expected engine pressure ratio shows rpm, exhaust gas temperature, and fuel flow that are all lower than normal. What is the probable cause?

  1. AThe EPR indication has a high reading error
  2. BThe turbine section has sustained heat damage
  3. CA compressor bleed-air valve has failed open
Show the answer and explanation

Correct answer: A. The EPR indication has a high reading error

  • A — correct A high reading error makes the gauge show target EPR before the engine actually reaches that thrust, so rpm, EGT, and fuel flow all fall below normal; the suggested action is to check the inlet pressure line from probe to transmitter for leaks.
  • B — incorrect Turbine damage or loss of turbine efficiency produces high EGT with low rpm and high fuel flow, not low readings across the board.
  • C — incorrect A bleed-air valve malfunction is listed with higher than normal exhaust gas temperature, rpm, and fuel flow, which is the opposite of the reported symptoms.

BACKGROUND

Turbine engine troubleshooting compares observed instrument values with those known to be correct for a given operating condition. Because engine pressure ratio (EPR) is the power-setting reference on many turbofans, an error in the EPR indication shifts every other parameter in a predictable direction. When the gauge reads high, the throttle is pulled back too far to reach the target number, so rpm, exhaust gas temperature, and fuel flow all come out low. When the gauge reads low, the same parameters come out high. For a high reading error the suggested actions are to check the inlet pressure line from probe to transmitter for leaks and to check the EPR transmitter and indicator for accuracy.

STUDY TIP

Work the logic in one step: if the power-setting gauge over-reads, the engine is actually producing less than you think, so everything else reads low. Practice reasoning in both directions before the test.

KEY POINTS

  • Low rpm, EGT, and fuel flow at target EPR points to a high reading error in the EPR indication.
  • The suggested action is to check the inlet pressure line from probe to transmitter for leaks.
  • A low EPR reading error produces the opposite symptoms, with all parameters high.

SOURCES

  • FAA-H-8083-32B ch10 "Troubleshooting Turbine Engines"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON TURBINE ENGINES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.