337 Cross feed (2) engines at once!!!/CPA related comments

[Guy Paris]

This was on CPA this am. I was not aware of this, hope I am not getting sometimers. Guy.... old72driver....

Ok, In my 1977 POH 337 G It states:
Fuel cross-feeding: Cross-feeding is limited to level flight only. If operating both engines from a single tank, cease cross-feed when level is withen: 50 lbs. of empty tank in use, or 50 lbs. of full in tank not in use.... Guy

T337G CROSSFEED BOTH ENGINES...
Dear Tom,
I recently had a very interesting experience in my P337. I was
cruising at +/- 12,500 when the front tank ran dry (a fuel imbalance by
line crew). Upon switching to the rear tank, the rear engine began to
quit! I immediately switched the front engine back to its own tank and
the rear engine regained power. I then "caged" the front engine and
proceeded to the nearest available airport to investigate and change my
shorts! I refueled and proceeded to my home airport without further
incident. Have you ever heard of this kind of problem with the
Skymaster before? My only thought is that the crossfeed lines could be
reversed. Before I spend several hours of expensive investigative
stupidity, I thought I would pick your brains as I have found you to be
the absolute best resource in aviation. You have saved me several times
my membership dues over the years.
Sincerely,
Rick,

Rick
What you did was a big no no. In your owners manual in section 2 on
page 2-3 is the important note you need to read and thoroughly
understand. "Crossfeeding is authorized for single-engine operation
ONLY. OPERATION OF BOTH ENGINES FROM THE SAME TANK IS PROHIBITED.
Simultaneous operation of both engines from the same tank could lead to
a double engine failure because of inadequate fuel flow."
What you learned is the fuel system supply cannot feed both engines
and the end result is a proven. Both engines will quit. I do not know
of anyone that has discovered what the max power settings the single
tank operation might be possible. That would be Test Pilot stuff and
way outside my area, I do not have or want that hat.
Tom Carr, CPA Tech Rep mailto:tom.carr@cessna.org
____________________________________

[Ernie Martin]

Guy:

I am very surprised by this. I guess that if the POH for your specific airplane says that, then you should NOT feed both engines from the same tank. However, if you've read the Fuel Management page in my www.SkymasterUS.com website, which applies mostly to '65-'69 337s, there is no such warning. Why? Because those models -- at least the ones I looked at -- didn't have any such restrictions on their POHs and because I've flown my old '69 337D routinely with both engines feeding off one tank.

Your message prompted to look at the POH for my normally-aspirated 337G with long-range tanks, and I could not find such a warning. Moreover, it seems sensible that you should be able to feed both engines from one tank, to allow you to fly with both engines running if through a fuel leak or for any other reason one tank goes dry in flight.

So, go look at your POH. If it doesn't have the warning, I think you can do it.

Ernie

[Guy Paris]

Ernie,
No restriction in my book. Guy....

[kevin]

The limitation *IS* present in the 1973 P337 owners manual, on page 2-3. Interesting, an important difference between different models of P337 perhaps...

Kevin
(not Keven, and not McDole ;-)

[kevin]

Gmas,

Wouldn't you want us to follow what is in the manual, at least for those of us that have 73 P337's? The complete text from the manual is:

"Crossfeeding is authorized for single-engine operation ONLY. OPERATION OF BOTH ENGINES FROM THE SAME TANK IS PROHIBITED. Simultaneous operation of both engines from the same tank could lead to a double engine failure because of inadequate fuel flow."

The capital letters are in the Cessna text, I did not add them.

You are usually so scrupulous about us following the manufacturer's written material, I am suprised at your stance in this case.

Kevin

[skymaster]

once the fbo ran out of fuel. yes he filled one side. took off switched to full tank. got to alttude and worried about the placarded fuel valves and what could happen during this night 350 nm trip . approaching runway switched back to both. The engines never sputtered. GMAS is probably right about the flight envelop cavitation and engines minimum fuel requirement. J

[Mark Hislop]

I suspect that the prohibition of operating both engines from one tank, and whether it works or not, is based on fuel flow. Another note in my POH (1973 P337) also warns that in the event of failure of engine driven fuel pump, the high-boots electric fuel pump will not supply enough fuel to maintain above 75% power. My manual also probhibits operation of both engines from one tank.

It really does seem as if there are major differences in the P337 fuel system and the earlier versions. This ought to turn into a good discussion.

Mark

[Damon Banks]

The POH for my 1974 T337G says the same as Kevin's above, that is, operation of both engines from the same tank is prohibited. Does seem to be a model specific case.

GMAS, I have one small issue with the turning warning...surely if the turn is co-ordinated, then there is no increased risk of the fuel tank outlet in the low (or high) wing becomming uncovered anymore than in level flight. During UN-coordinated flight though, (straight and level or turning) I agree that there would be a risk.

Regards,
Damon

[Kevin McDole]

And in the 1976 P337 POH, it has a different statement regarding cross-feeding. From Page 2-8:

Fuel Cross-feeding: Cross-feeding is limited to level flight only. If operating both engines from a single tank, cease cross-feed when level is within:
50 lbs. of empty in tank in use, or
50 lbs. of full in tank not in use.

Apparently, the revisions of the fuel system changed the cross-feeding limitations over the years, so one answer does not fit all aircraft.

[Bob Cook]

On the subject

1) If one engine burns 140 lbs on takeoff then why cannot two engines support the same during cruise.

2) Perhaps there is not enough capacity of the pump to draw from the low wing during a turn, therefore the level flight limitation.

3) Still the most prudent thing would be to find the closest airport with sufficient runway to land.

4) Other than being out of fuel in one tank, there would be no valid reason to run both engines from one tank.

5) If there was any kind of fuel contamination (ie. water in fuel) then it would make life worse.

6) My way of thinking would be to pull the appropriate mixture (cut off) as opposed to playing with the fuel selector.

MHO

Bob

[Ernie Martin]

Everybody, please relax. I sense some tension, and we don't want this to be a repeat of the lean-of-peak discussion.

Simply put, there are some differences of opinion here. Which is healthy. And I think everyone is in agreement: if the POH says don't do something, you shouln't do it. End of story.

Ernie

[SkyKing]

Why snivel over spilt milk. It seems everybody and their dog (old cliche') has to be a "dues paying member" of this or that in order that they feel important, like AOPA or CPA or what-have-you, and wear their little sticker. It makes no never mind to me, and while most of these membership-driven organizations charge a fee to join and belong to their exclusive group so that they can send you their glossy magazine filled with advertisements and get their so-called timely information, my sense of joining and belonging is owning a 337 like the rest of you, and owning the materials that Cessna makes available in order to fly and maintain the Skymaster, and being able to actively interact with the rest of you without a fee attached or somebody trying to make a quick-buck like the middle-man, so that we can get the best from these machines and enjoy flying. THAT's what I consider my fees for belonging and joining with the rest of you. I don't need AOPA or CPA, or the much touted Cessna Owner Organization and their magazine which is published by Aircraft Owners Group, which is a division of Jones Publishing Group that has similar dues-paying, membership-driven organizations for Beech and Piper... oh, and you thought they were exclusive for "Cessna Owners"... what a laugh. All they sell is a "membership" and you get a slick monthly magazine which they are able to publish only because of all the full bore retail ad space they've sold to dealers and manufacturers. Whoopy. Now I hear that certain personages have "maligned" some one of the publishers and writers and head-honchos of one of these organizations. I wish people would check their dictionary before using such words. "Malign", according to Webster's, is defined as: "adj 1 : evil in nature, influence, or effect (hindered by ~ influences>; also : MALIGNANT 2 : moved by ill will toward others." Now, I read what GMAs stated, and I didn't grasp that he meant any of that toward the head-honcho over at that other place. As a matter of fact, I got kind-of-a-laugh as I read it. Sort of a humerous put-down, somewhat humiliating perhaps, but knowing the ground we've been over before, no big deal... just like if you stepped in the cat's milk bowl and it spilt it. No... we... ALL of us that are over here at the SOAP site don't really need the pay-for-this and pay-for-that nickel and diming that goes on with all those other dues-paying "I want to be a member and belong..." organizations. We have the best right here and right now, and we've already paid our dues to be a "member" and "belong"... We're the 337 Skymaster owners and operators. As such, our dues to belong have already been paid for and as long as we can keep an internet connection, this is so much better than a printed magazine, and you get answers to your questions generally as quickly as the time it takes to write them. And BTW, do any of you really understand the VALUE of having GMAs around here? If you don't, next time you have a problem with your plane, walk over there across the ramp and talk to the chief Mr. Fix-It wrench twister or call the head-honcho over at so-and-so, and see what kind of an answer they give you. Nuff said.

SkyKing