During an engine restart procedure, what are the purposes of a.) throttle back to idle and b.) primer "in and locked"? I was making some study flashcards today for Emergency Procedures in the Cessna 162 POH, and realized that I don't quite understand steps 2 and 6 of the ENGINE FAILURE DURING FLIGHT (Restart Procedures):

  1. Airspeed .................. 70 KIAS (best glide speed)
//2. THROTTLE Control .......... IDLE (pull full out)
  3. CARB HEAT Control Knob .... ON (pull full out)
  4. FUEL SHUTOFF Valve ........ ON (push full in)
  5. MIXTURE Control ........... RICH (if restart has not occurred)
//6. PRIMER (if installed) ..... IN and LOCKED
  7. MAGNETOS Switch ........... BOTH (or START if propeller is stopped)


I think understanding the why behind all of the checklist procedures will help me remember them better.
Source

Idling, or closing the throttle, might help break up any ice that may have formed and caused the engine to quit. That's why it's followed by Carb Heat On.

Also, a failed engine (of any type) is best restarted at idle power. Otherwise the extra fuel will either flood or overheat the restart. But nevertheless, always stick to whatever the checklist says.


  Throttle ice forms when your throttle is partially closed, typically between cruise power and idle. As air moves through the the Venturi in your carburetor, it decreases in temperature, condensing water vapor from the air. The water then starts freezing to the carburetor parts, restricting airflow. Eventually, you'll start losing RPM or manifold pressure, your engine may start running rough, and if the ice gets bad enough, your engine will quit.




If a primer is inadvertently left in the pulled / unlocked position, it may flood the engine with fuel.