What effect does a blocked EPR outlet probe have while climbing?

• A. Over-read causing underspeed
• B. Under-read causing an overspeed
• C. No effect
• D. Readings oscillate

Answer: (B)

A block on the EPR outlet probe causes the exhaust pressure input to the EPR sensor to be lower than the true value. The EPR gauge then under-reads the actual thrust being produced. During a climb, pilots use the EPR to set thrust levels; seeing a reading that’s too low prompts them to advance the thrust levers to reach the target. That extra power can push the engine toward an overspeed, even though the displayed EPR remains low. So the effect is under-reading that can lead to an overspeed. It wouldn’t typically cause the reading to oscillate, and it certainly isn’t no effect.