Kick the Tires, Light the Fires: How to Start a Cessna 172

Most people with a driver’s license are familiar with the process of starting their car and getting it ready to hit the road.  But few people understand what is involved in starting up an airplane, specifically a Cessna 172.  So, in this article, we’re going to show you how to start a Cessna 172.

According to the Cessna 172SP startup checklist, starting the aircraft engine involves the following steps:

1. Open the throttle ¼ to ½ inch.
2. Turn the master switch ON.
3. Turn the fuel pump ON.
4. Position the fuel mixture to full RICH until stable fuel flow is established. Then change it to full LEAN.
5. Turn the beacon light ON.
6. CLEAR the propeller area.
7. Turn the ignition switch to START.
8. When the engine starts, set the mixture control to full RICH.
9. Turn the ignition switch back to BOTH.
10. CHECK the oil pressure.
11. Turn the Avionics Bus 1 and Bust 2 ON.
12. Turn ON and SET the Radios.
13. Turn the transponder ON.

Let’s dive a bit deeper into each of these steps so you’re not only able to get your simulator engine started, but you understand what’s going on in each of these steps.

Aircraft Checklists:

I will never forget the time I took some friends flying.  It was their first time in a small airplane.  I took out my checklist and was dutifully going through all the steps necessary to ensure a safe and successful startup, when someone in the back seat exclaimed, “You don’t know this airplane well enough to start this plane without using the instruction book?!?!?!” 

I was taken aback by this!  It never occurred to me how someone who doesn’t understand aviation might perceive me using a checklist.

Unlike the automotive world, pilots never assume we’ve flown enough to “just know” how to fly the plane.  If all the steps to get airborne were left up to our memory, we might just forget something.  And that one forgotten step might be the difference between arriving safely and making an emergency landing in a cornfield…or worse!

Because of this, the aviation community uses checklists.  These lists help us go through nearly all the processes of flying the aircraft in a safe and organized way.

This is why we’ll be following the checklist today as well!

Before We Light the Fires:

Starting the engine of our Cessna 172 is NOT the first thing we do after walking out on the ramp.  Long before we turn the ignition, we will have done our preflight inspection of both the interior and exterior of the aircraft.  We also need to make sure our switches and equipment are on the proper settings before we even begin the engine start portion of the checklist.

Make sure to consult the Cessna 172SP checklist before trying to start the engine.

1. Throttle: OPEN ¼ to ½ Inch:

The steps we are following in this article are specific to the Cessna 172SP, which is a fuel injected engine.  The starting procedures will be different for Cessna 172’s that are carbureted.

Unlike a car, the throttle on a Cessna 172 is not a pedal on the floor.  It is a black-handled plunger near the bottom-center of the instrument panel.  If we pull this plunger all the way out, the engine is set to full idle, much like taking one’s foot completely off the gas pedal of a car.

To start our Cessna 172, we want to open the throttle just a little more than idle.  A great way to judge how much we’ve moved the throttle is to bring it all the way back to idle.  Then, we place our index finger on the shaft of the throttle plunger and up against the panel, where the shaft goes into the panel.  Then, draw our finger back along the shaft until it is ¼ to ½ inch away from the panel.  Now, without allowing our finger to slide on the throttle shaft, we push the throttle control in until our finger is touching the panel again.  This ensures we get an accurate ¼ to ½ inch of throttle.

2. Master Switch: ON:

The master switch is a big red electrical switch on the bottom left corner of the panel.

Unlike cars, the electrical systems in aircraft work independently of the ignition system.  In other words, the electrical power used to turn on the lights, instruments, radios, etc. is different from the electrical power used to give spark to the spark plugs.

The master switch controls the electrical power from the aircraft battery to the lights, instruments, radios, engine starter motor, etc.

When we turn the master switch to “ON” we make sure that when we turn the ignition key, there will be electrical power to the starter motor.

3. Fuel Pump: ON:

The fuel pump is controlled by a toggle switch which is often near the light switches.  Turning on the fuel pump pressurizes the fuel system so that there is sufficient fuel supply to start the engine.

4. Mixture: RICH (Until Stable Fuel Flow Indication), then LEAN:

The mixture control is the red handled plunger right next to the throttle control.

Another difference between cars and airplanes is how fuel flow is controlled.  Aircraft operate at a wide variety of altitudes.  The higher the aircraft climbs, the less oxygen is in the air.  If fuel is going to burn in the engine, it needs to be mixed with oxygen at a very specific ratio. 

The airplane’s mixture control allows the pilot to adjust the amount of fuel being combined with the air in order to maintain this ratio, which is called the stoichiometric ratio.

When we start the airplane engine, we want it to have a little more fuel than normal.  So we open the mixture control to full rich by pushing it all the way in toward the panel.  This allows the fuel that the fuel pump is pushing into the cylinders at the maximum rate.

We are only going to leave the mixture at full rich for a moment, until we see a positive fuel flow reading on the fuel flow gauge.  Then we will reduce the mixture to full lean.

5. Beacon: ON:

The beacon light control is one of the toggle switches along the bottom left side of the panel.

Visibility is important for operating an aircraft at an airport.  It is important to let other aircraft know when our engine is running and we are operational.  The red beacon light, which is located on the top of the vertical stabilizer, lets everyone know to keep an eye on us.

6. Propeller Area: CLEAR:

Before we start the engine and get the propeller spinning, we want to give anybody anywhere near the aircraft the opportunity to clear the area.  In order to clear the area, we open the window and say in a loud voice, “Clear Prop!”

7. Ignition Switch: START:

This is the moment of truth!  With our right hand on the mixture control we turn the key in the ignition switch into the START position.

When we do this, the starter motor will engage.  The propeller will begin to spin.  Within a couple of seconds, one of the cylinders should fire and the engine will roar to life!

8. Mixture: RICH (Advance when Engine Starts)

When the engine begins to run on its own power, we need to do 2 things very quickly.  The first thing we need to do is to push the mixture control all the way in to the full RICH position.  This will give the engine the proper amount of fuel it needs to run normally.

9. Ignition Switch: BOTH

The second thing we need to do very shortly after pushing the mixture control to full RICH, is to take our left hand off the key so the ignition switch returns to the BOTH position.  This will disengage the starter motor. 

Like starting a car, it is important to get our hand off the ignition switch very soon after the engine starts so that we don’t damage the starter motor.

10. Oil Pressure: CHECK

Now that the engine is running, it is very important to make sure that oil is getting into the engine to lubricate the parts.  We can check this by checking the engine oil pressure gauge. 

The oil pressure gauge is often located on the far left side of the panel, near the bottom.  However, the location can be different in different aircraft.  So it is important to know where it is in your aircraft before starting the engine so that you can check oil pressure quickly after start up.

The oil pressure is correct when the needle is pointing somewhere in the green arc.  While the engine is set at idle power, the needle will most likely be near the bottom of the green arc. 

If you have low our no oil pressure, shut of the engine quickly by pulling the fuel mixture back to full lean.  It is important to have the engine looked at by maintenance personnel to avoid any damage to the cylinders or other parts.

11. Avionics Bus 1 and Bus 2: ON:

The avionics are the electronics used for communications and navigation.  Now that our engine is running, we have enough electrical power being produced to turn on the avionics without over straining the battery.

The avionics bus 1 and bus 2 switches are the white switches down near the light switches.

12. Radios: ON AND SET:

Our communication radios often have their own power switches.  If the radios haven’t turned on by turning on the avionics bus 1 and 2, make sure to use the other power switches to power up the radios.

13. Transponder: ON:

The transponder is the radio that communicates with air traffic control’s radar equipment.  It helps ATC know where we are and what altitude we’re flying at. 

The transponder, along with its power switch is typically located near the bottom of the avionics. 

Congratulations!!! 

You’ve officially started the engine in a Cessna 172SP! 

I highly recommend using a flight simulator like X-Plane 11 to help you practice procedures like starting the Cessna 172.  It allows you to go through the checklist over and over again without risking damage to expensive equipment or costing you any money!

Warning:

This article is intended for informational purposes only.  This is not sufficient information to safely operate an aircraft.  Do not use it to operate an aircraft without the oversight and instruction of a FAA Certified Flight Instructor!