Indications of an engine bleed-air valve malfunction?

Indications of an engine bleed-air valve malfunction?

• A. Lower-than-normal EGT and lower RPM
• B. Higher-than-normal EGT, higher RPM and higher fuel flow
• C. No change in readings
• D. Throttle stuck in idle

Answer: (B)

Bleed-air valve problems upset how the engine uses and meters air from the compressor. If the valve isn’t regulating bleed air properly, the engine experiences abnormal air flow and a mismatch between the air entering the combustor and the air actually being used for the engine’s operation. To hold the commanded thrust under that disturbance, the fuel-control system ends up delivering more fuel, which raises the turbine inlet temperature. That extra fuel and hotter combustion push the exhaust gas temperature higher, and the engine spool responds by increasing speed (RPM) as it tries to maintain power. The net result you’d see is higher-than-normal EGT, higher RPM, and higher fuel flow. The other scenarios don’t fit a bleed-air valve fault: there wouldn’t typically be no change, and a throttle-stuck-in-idle fault behaves mechanically rather than through the bleed-air system.

Bleed-air valve problems upset how the engine uses and meters air from the compressor. If the valve isn’t regulating bleed air properly, the engine experiences abnormal air flow and a mismatch between the air entering the combustor and the air actually being used for the engine’s operation. To hold the commanded thrust under that disturbance, the fuel-control system ends up delivering more fuel, which raises the turbine inlet temperature. That extra fuel and hotter combustion push the exhaust gas temperature higher, and the engine spool responds by increasing speed (RPM) as it tries to maintain power. The net result you’d see is higher-than-normal EGT, higher RPM, and higher fuel flow. The other scenarios don’t fit a bleed-air valve fault: there wouldn’t typically be no change, and a throttle-stuck-in-idle fault behaves mechanically rather than through the bleed-air system.