What does the ENG APR button do?

 

Michel Labarre.

What does the ENG APR button do?

 

Michel Labarre.

 

APR stands for Automatic Power Reserve and what it does is automatically increases the power of the running engine in the event of an engine failure on takeoff and automatically feathers the failed engine. So it needs to be armed for takeoff.

Just to expand on what Luke said, here is how the APR system actually increases engine power on the remaining healthy engine in the event of an engine failure:

Automatic power/performance reserve (APR) system is used to increase engine power in the event of a single-engine failure on take-off or landing. This is accomplished by adding more fuel through the enrichment torque motor. With the APR switch in the “ARMED” position, RPM lever at high, and power lever above 65% power, if the integrated electronic control (IEC) detects a decrease in torque on the opposite engine, it will open the enrichment valve to obtain a torque value 10% higher than target torque, but limited to a maximum torque of 100%. The IEC will also increase the Exhaust Gas Temperature Variable Red Line (EGT VRL) by a minimum of 38°C to prevent the Torque and Temperature Limiter (TTL) from bypassing the extra fuel.

As Luke also said, the APR will autofeather the failed engine too.

 

Notes on usage of APR system:

• If it is the first flight of the day, the Captain will test the APR OVERRIDE, push the APR O/RIDE caption and note the illumination of the white APR O/RIDE light, an increase in fuel flow, RPM and EGT. The Captain will then deselect APR O/RIDE and note a return to normal fuel flow, RPM and EGT

• APR is armed as part of the after-start checklist, if required (APR does NOT need to be armed for every takeoff, in real life this is determined by an airport analysis and airline SOP). It MUST be used for takeoffs in icing conditions. A reduced torque takeoff cannot be performed if APR is armed for takeoff.
  
• Based on the above two bullet points, the after-start checklist responses for APR are "TEST/ARM", "TEST/OFF", "OFF" and "ARMED".
  
• APR MUST be armed for every landing, as part of the decent/approach checklist.
  
• APR should not be operated for more than 5/10 minutes, as the engine is operating beyond its normal in-service limits. Every time the APR system is activated it adds four cycles to the engines log book, and each hour of APR operation will add fifty to the log book.
  

Thanks for the explanations. Very educational.

 

Michel Labarre.