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Author Topic: Fuel and Twin Commanders (Part 3) - an important read...  (Read 2719 times)

Russell Legg

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Fuel and Twin Commanders (Part 3) - an important read...
« on: October 10, 2015, 12:32:35 am »
I did manage to squeak another 7.5 (148.5 total) gal after it sat over night,
>but that is still a bit short??
>Harry Merritt, they guy who sold it to me, suggested it was missing a blatter.
Looking at my illustrated parts catalog, I only show the typical 5 cell
exactly like my 500B. The catalog refers to 500 series, 560, 680F and FP.
Is there any difference between your 680E and the 680F?
Chris's chart says 223 gallons for the 680E, if this is true then you
might have
a completely different fuel system than the diagram that I'm looking at.

My maintenance manual says the fuel system is comprised of 5 cells which
hold a
total of 150-159 gallons. If you're on the lower end then your close.
When I refueled after the fuel cell installation, I was on the higher end
of 157 gallons.
(I made sure the laces were tight and properly positioned).

I'm sure Morris can fill in the details.
Hope this helps.

THANKS RANDY............

             The fuel systems on the 500B and the 680E are the same. 
Interesting that your book gives a rang of 150-159.   Mine, for the 680E,
says 155-159??  Anyway, I know what it holds now so I will always use that
empirical number.  On the bright side, I can add 40# to my "full fuel" cabin
load!!  Thanks!  Jb

Fellow Commander Pilots:
I read with great interest concerning the amount of fuel, or lack of fuel the
Commander is designed to hold.
Allow me to discuss a "Deadly Problem".  And please respond, as I will take
all comments to the Insurance Companies, as well as my friend and yours,
Richard Collins, editor at large for FLYING Magazine.
Jet Fuel in Piston Engines.
Over the last 30 days, I personally know of 2 aircraft that have been
Can you quess the aircraft?
Cessna 421 and Aero Commander.
The Cessna 421, was on the take off roll when the engine did not develope
The Commander was taxing back to the FBO to retrieve a package.
 In the case of the 421 the lineman did not admitt his mistake until pressed
by the FBO manager.  He actually, after noticing jet fuel had been pumped,
went back to the Av gas truck and completed the refueling with Av gas.
Another example of minimum wage employees, with lack of training working on
the potential of Million dollar losses, not to mention the people we love
most...Our family and friends...
Please sound off...I need the data.
Gary Tillman-Pres.

The fuel systems on the 500B and the 680E are the same.   
Interesting that your book gives a rang of 150-159.   Mine, for the 680E,
says 155-159??

The 680E does have two additional "outboard" tanks with a capacity of about
33.5 gallons each, right?

The "Main" fuel system is identical to a 500 series; 5 bladders holding
around 156 gallons.

Just wanted to clarify that point for everyone watching this thread.

This happens so frequently, that when I was giving Commander initial
training, I admonished my clients to always stay with the airplane during

The Cessna products set themselves up with the word "Turbo" on the nacelles
in the mid 70s, which you will notice is no longer part of the paint

The Commanders suffer because to a young line service professional, they
look like a Turbo Commander.

The GAMA (and FAA) placards, nozzle restrictors, etc. are helpful, but I
know of an instance in the Kansas City area where the fueler worked extra
hard to get a jet nozzle into a piston model fuel port.  There's no
stopping yankee ingenuity nor poor reading comprehension.

The bottom line is education and if you don't know that the FBO and fuel
person  knows your piston Commander, STAY WITH THE AIRPLANE DURING FUELING.
 Besides, as Big Al and others have mentioned, the only way to get a true
top off is to let the tanks appear to be full, then wait a period of time
and fill again.

By being there, you not only assure the proper fuel, but that you're
getting the last 30 minutes of fuel you're planning on.

For one of the earlier TCFG fly-ins, I created a training aid for the host
FBO.  If there's enough interest, I'll upload it to the website and
individuals can download and print it.

It's a rather large Word document with too many color graphics, but it's
already created, so why reinvent the wheel?

Keith S. Gordon
Very early on in flying my 560 I got a lot of comments from line KIDS about how come mine looks different than other commanders and had trouble convincing them that it did not take jet A.
As a result I have started telling line personell everywhere I fill up. In spite of this recently I had to stop an attendent in Punta Gorda Florida as he climbed the ladder to top off my plane with a nozzle connected to a truck that said "jet A".
This happened even though I have a HUGE sign next to the filler cap that says av gas only and clearly my orifice was too small for the monster schnoz this guy was about to stick in it. Now I never let anyone fuel it unless I am watching.

Hi Gang, Just a little note,my ole girl holds 233 gallons and at an average
consumption(at 65% power-170mph)of 32-34 gph,her bladder lasts much-MUCH
longer than mine.

I tried to point out that the Commander cockpits are set up for a very
efficient and natural flow pattern ... unlike the factory checklist sequences.

But that's old news.  On the topic of boost pumps, here's some food for
thought:  Continental engines used to have pressure activated boost pump
output rates.  If a lower than normal fuel pressure was sensed, the electric
fuel pump would kick into high.  That also happened when it wasn't needed and
that flooded engines and caused incidents with fatalities.

That's NTSB speak for crash -- and an AD removed that system from most
installations, if memory serves me. (CE300s, CE400s and AC-500A come to mind.)

Lycoming engines don't seem to suffer from this problem and "boost pumps on"
for takeoff is a good thing.

However. (You all knew this was coming, didn't you?)  Of the partial power
losses I've had on approach in Lycoming and Continental powered twins, all
were caused when boost pumps were turned on.

It is true that something was out of adjustment, somewhere, and please don't
come at me with the old bromide of "well, you should have flown a better
maintained airplane."   All airplanes are in a state of semi-partial
perfection (gads, I'm diplomatic), all of the time.

I am happy to NOT use boost pumps on landing, turning them on as a reaction
to power loss instead of inviting power loss due to them being on.

So there you have the classic struggle between textbook theory of what's
right vs. field experience.  I'm not sure which holds the moral high ground,
but I know which method keeps the engines running.

Keith S. Gordon

Most of my fuel pressure problems (in flight) on the 680-F Series were due to
clogged screens in the Simmonds fuel injection units.

These fine mesh screens must be ultrasonically cleaned - - and more often
than you would think.  Perhaps that could help, but I have usually seen the
need for boost pumps around the 8000' level in the 680-F series, as well.
I don;t know about other models, but my AC560 with GO-480's has an often overlooked recurring AD to tighten the screws on the engine mounted fuel pumps every 25 hours.  I have this done at the same time I have my oil changed.  I have never had fuel pressure problems, in over 250 hours of flying mine.

My guess would be that the screws loosen, even with the safety wire, allowing air in the system.  This could cause over-reving, and low fuel pressure