How does engine thrust respond when the EEC mode is manually changed from NORM to ALTN?

How does engine thrust respond when the EEC mode is manually changed from NORM to ALTN?

• A. Thrust decreases when alternate mode is selected manually.
• B. Thrust stays the same when alternate mode is selected manually.
• C. Thrust increases when alternate mode is selected manually.
• D. Thrust becomes unstable when alternate mode is selected manually.

Answer: (C)

Switching from NORM to ALTN moves the engine control into an alternate control path. In ALTN the EEC uses an alternate set of signals and limits, which reduces some of the automatic protection and allows more fuel to flow for the same commanded schedule. That means the engine can deliver more thrust than in NORM. It’s like giving the engine a bit more authority to produce power when normal protections might be too restrictive for certain abnormal situations. So, when you manually select ALTN, the thrust tends to increase because the alternate control mode permits higher fuel delivery and power output. The other possibilities—thrust dropping, staying the same, or becoming unstable—aren’t the behavior designed for ALTN, which is why increasing thrust is the best answer.

Switching from NORM to ALTN moves the engine control into an alternate control path. In ALTN the EEC uses an alternate set of signals and limits, which reduces some of the automatic protection and allows more fuel to flow for the same commanded schedule. That means the engine can deliver more thrust than in NORM. It’s like giving the engine a bit more authority to produce power when normal protections might be too restrictive for certain abnormal situations.

So, when you manually select ALTN, the thrust tends to increase because the alternate control mode permits higher fuel delivery and power output. The other possibilities—thrust dropping, staying the same, or becoming unstable—aren’t the behavior designed for ALTN, which is why increasing thrust is the best answer.