Primers? Why?

mshac · #1 10-04-20, 10:51 PM

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 · #2 10-05-20, 09:58 AM

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 · #3 10-05-20, 07:35 PM

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 · #4 10-05-20, 08:59 PM

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 · #5 10-26-20, 08:37 PM

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 · #6 10-26-20, 08:41 PM

Quote:

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...

rhurt · #7 10-26-20, 09:33 PM

Agree. I would rather remove the primers from my airplane

JimC · #8 10-27-20, 02:25 PM

"If you were to use the manual primers because the electric fuel pump was inop. you would be ILLEGALLY flying"

Devil's advocate - why is this illegal?

I'm not saying it's a good idea, but I don't think it's illegal. 337s don't have MELs.

mshac · #9 10-27-20, 02:37 PM

Jim is probably right - I don't recall "fuel pump" as being on the list of required items for either VFR or IFR flight. I'd compare it to flying NORDO VFR - completely legal in non-controlled airspace, but not recommended. And for the non-airline types, an MEL is a Minimum Equipment List - Everything on the list has to work in order to dispatch the airplane. Things like coffee pots and reading lights are not on the list, but I would imagine fuel pumps would be.

JAG · #10 10-27-20, 05:33 PM

Such a great topic - but maybe not everyone will take interest.

I am not an expert on FAR 23 Certification Standards, but there must be some intent of Cessna for the auxiliary pump to be required equipment; they have put them on separate breakers and stipulate their use in the operating manual to provide fuel flow (HI) in the case of engine driven pump failure, or even vapor elimination in flight.

I can't make a comment if you would be legal or illegal - I don't have enough knowledge on the certification side of things. But my experience would tell me that this is likely required equipment for flight - as the intended use of the auxiliary pump is clearly required in the operating handbook for emergency procedures. For me personally, I would not take off without an aux pump working. I view the use of the pump as a mitigation for a number of fuel related problems - and I prefer to operate the aircraft the way Cessna had designed it.

Regarding MELs (an area I do have expertise in), there actually is a Master MEL published by the FAA for the 336/337. Not required for us to use in private operation, but it is an interesting to read what is, and what is not on it.

Jeff

skymstr02 · #11 10-30-20, 10:38 PM

With only two primer nozzles per engine, and they are not on cylinders, I challenge you to start an IO-360 without a boost pump. Look where those nozzles are on the engine
When your engine driven pump fails in flight, how do you propose to keep that engine running?

JimC · #12 11-03-20, 01:19 PM

Quote:

Originally Posted by JAG

Such a great topic - but maybe not everyone will take interest.

I am not an expert on FAR 23 Certification Standards, but there must be some intent of Cessna for the auxiliary pump to be required equipment; they have put them on separate breakers and stipulate their use in the operating manual to provide fuel flow (HI) in the case of engine driven pump failure, or even vapor elimination in flight.

I can't make a comment if you would be legal or illegal - I don't have enough knowledge on the certification side of things. But my experience would tell me that this is likely required equipment for flight - as the intended use of the auxiliary pump is clearly required in the operating handbook for emergency procedures. For me personally, I would not take off without an aux pump working. I view the use of the pump as a mitigation for a number of fuel related problems - and I prefer to operate the aircraft the way Cessna had designed it.

Regarding MELs (an area I do have expertise in), there actually is a Master MEL published by the FAA for the 336/337. Not required for us to use in private operation, but it is an interesting to read what is, and what is not on it.

Jeff

I agree with all of the above, except for one thing: Regardless of intent (or wisdom) I don't think there's any way Cessna can make it legally required for part 91 without an AD.

I think 91.213 (d) covers it.

23.991(b) says that a backup pump is not required if the fuel injection pump is part of the engine.

Learjetter · #13 11-06-21, 01:32 PM

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 · #14 11-07-21, 07:25 PM

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 · #15 11-08-21, 05:59 AM

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.