Primers? Why?

[mshac]

My 1969 Cessna 150J had a primer. You would use it before you started the engine. There was no electric fuel pump, so it made sense.

Our Skymasters all have electric fuel pumps. What is the purpose of having primers installed?

The only reason I can think of is to be able to start the engines with no working electrical fuel pump.

I've never seen primers in a Baron, or any other twin.

Am I missing something?

[JAG]

Hi Mark,
The primers are related to cold weather starting procedures. It may be in your owners manual (POH) - it is in mine. But yes, practically it is also an alternative to a fuel pump if you are in a bind.

Jeff

[cessnadriver]

FYI. I asked the same question REF: manual primers. If you were to use the manual primers because the electric fuel pump was inop. you would be ILLEGALLY flying. Because if you did take-off and had an mechanical fuel pump go out then there is a complicated procedure to cross-feed the inop. engine fuel pump. See the other Skymaster web site www.skymasterus.com for detailed explanation.
Thanks, BILLS

[mshac]

Later model 337's have a simplified fuel system. There are no "AUX" tanks, only a single main in each wing. No reason to ever have to touch the fuel selectors unless you're wanting to cross-feed for some reason. Nothing at all "complicated" about it.

[rhurt]

So you can hand prop the plane with a dead battery. A friend of mine has hand propped them several times but there was always enough battery power to run a fuel pump.

[mshac]

Originally Posted by rhurt

So you can hand prop the plane with a dead battery. A friend of mine has hand propped them several times but there was always enough battery power to run a fuel pump.

True enough, but I've never been a fan of hand-propping anything much larger than a Cub...

[Learjetter]

In the middle of installing GI-275s as EIS in my ‘77 air breathing G model and we collectively can’t determine the function of the primers. Equipment list shows them as A (auxiliary), not even optional. No normal or emergency checklist calls for their use. The fuel system and engine descriptions in the POH don’t mention them. Can’t dispatch without electric aux pumps, which we check every engine start.

We’re considering removing all the capillary tubing and the primers themselves. Any thoughts from the brain trust here on the issue? Can primers be removed?

[cessnadriver]

Learjetter.
I removed mine with a simple airframe log entry! I'm trying to eliminate as much fuel in the cockpit. Currently only the fuel flow gauges are supplied with fuel lines. As you probably know, you cannot fly if you have a aux fuel pump inoperative, so you could start a engine with the manual prime, but CAN'T fly. That's now I justified removing mine. I hope this helps.
PS: The manual primes ARE NOT on the minimum equipment list!
Regards,
Bill Story
'65 C337 owner, pilot and A&P

[mshac]

Issue was covered pretty good here:

http://www.337skymaster.com/messages...hlight=Primers

Key points-

1. Primers may be very helpful in an extreme cold-start situation. But unless you plan to operate in very cold weather, you are likely safe to remove your primers.

2. Essentially, a reading of 91.213 (d) and 23.991(b) will make it clear that aux. fuel pumps are not required equipment on fuel injected aircraft:

23.991 (b): Emergency pumps. There must be an emergency pump immediately available to supply fuel to the engine if any main pump (other than a fuel injection pump approved as part of an engine) fails. The power supply for each emergency pump must be independent of the power supply for each corresponding main pump.

So yes, you could legally fly without an electric aux pump operating, but I would think only in a real pinch would you want to do so.

[Learjetter]

MShac -- good point about the other thread, I should have continued the previous thread. As penance, I merged the two (I hope it worked!)

So, to sum it all up:

Why remove them?
- To reduce the complexity of the fuel system plumbing and keep other twin pilots asking why they're there.
- To remove additional sources of fuel leaks in the engine compartments above the cylinders.
- To eliminate any source of fuel leak from the manual primer system at the pedestal or under the floor.
- To improve the front fuel strainer longevity by reducing the connections to it and reducing the sources of fuel that may contaminate it.
- Gain ~ 2 lbs of useful load.
- Gain additional lower pedestal space for future equipment installation.

Is it safe to remove them?
- My POH does not reference manual primers in any system description nor in any normal or emergency checklist, nor in any "Kinds of Operations". Therefore there is no operating requirement to ever use them. The electric AUX pumps are checked on every engine start and are specifically described as for engine start and to serve inflight as a backup to the engine-driven pump.
- Aircraft's "general" equipment list refers to the primers as (A) meaning "optional equipment items which are in addition to required or standard items"
- Aircraft-specific equipment list has "Engine Priming System" on it, but I would contend that includes AUX pumps vice only the manual primers. In short, the engines require a priming function, but the specific equipment to fulfill that role can be the electric AUX pumps OR the manual primers (my opinion).
- FAA MMEL -- confirmed the manual primers aren't on it.
- 14 CFR 91.213 does not prohibit removal of the manual primers

I think we'll consider removing them with a logbook entry like Bill did.
-LJ