Misc C172 Information

Question 1

How many fuel pumps does the C172S have?

Answer 1

2

1. Engine-driven fuel pump
2. Electrically-driven fuel pump (auxiliary fuel pump) - used for priming or backup to the engine-driven fuel pump

Question 2

Describe the journey fuel would take from tank to cylinder

Answer 2

From reservoir tank, fuel flows through:

1. Auxiliary Fuel pump
2. past shutoff valve
3. through fuel strainer
4. through engine-driven fuel pump
5. to the fuel control unit

which disperses to the cylinders

Question 3

There are a lot of drain valves on a 172s.

How many do you need to check?

Answer 3

On the first flight of the day you need to check all.

Otherswise, you could just check drain 3 at a bare minimum.

Same for under the fuselage, as there are 3. Just the main gasculator if no contamination suspected is fine.

Question 4

What happens when the aux pump and engine driven pump are both on?

Answer 4

During flight, both aux and engine-driven pump being on will slightly enrich the mixture.

So it’s used on takeoff and landing, and turned off once you’re at a decent altitude where you’d have enough time to turn it back on if your engine driven pump fails

Question 5

If during flight you experience the fuel flow indicator showing a bit of a wobble and the engine is running a bit rough on a very hot day, what could be happening and what is the solution?

Answer 5

If the fuel flow indicator is showing a bit of a wobbly flow with a rough engine in hot weather, you lightly have some vapor suppression. Turn the aux fuel pump on to build up the pressure, force out that air in the lines, and establish stable flow again.

Question 6

In a C172S there are two main buses, one being the essential Bus. During an electrical failure, you may have to turn off a bus to conserve battery. What do you need to make sure you do before switching to the essential bus only?

Answer 6

Before turning off Electrical bus 2 in order to only use Bus 1, you need to ensure COM and NAV are in COM1 and NAV1, as these are the comm systems on the essential bus. COM2 and NAV2 are not on the essential bus, and therefore you need to switch off of them before turning off Bus 2.

Question 7

What should you do if you flood the engine?

Answer 7

1. Mixture idle cutoff
2. Throttle open halfway
3. Engage starter till engine starts
4. Once engine starts, mixture full rich
5. Return throttle to idle