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Old 05-13-2010, 07:02 AM   #1 (permalink)
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Default Cessna 421B Fuel System

Does anyone have any useful information/tips for the 421B and specifically the fuel system. (Which looks like the engineer had a seizure when drawing the schematics)...gotta ferry one soon.

I'm pretty familiar with the 421C...

Here's what I understand so far:

"There are a total of six fuel tanks. The tip tanks are the main tanks, 300 pounds of fuel in each. The internal wing tanks are the auxiliary tanks, 290 pounds of fuel in each. Lastly, there were the wing locker tanks that are situated behind the engines. These each carried about 156 pounds of fuel. Take offs and landings are performed using the main (tip) tanks. The reasoning behind this was that there were emergency back-up pumps in those tanks so that in the event of an engine-driven pump failure these electrically-driven pumps would kick in. There are switches that are placed in the "armed" position for takeoffs and landings that allow this transfer of pumps to take place automatically in an emergency situation."



"After the main (tip) tanks are drawn down to half-full, the engines would be switched to draw fuel off of the auxiliary (wing) tanks. Because of the fuel system design, the fuel pumps deliver more fuel to the regulators than is necessary. This excess fuel is returned to the main (tip) tanks, not, as you would think, the auxiliary (wing) tanks. By the time the wing tanks are completely drawn down, the main (tip) tanks will be full again from this excess return. At this time, the main tanks are once again selected as a fuel source. Once the mains are once again drawn down, the fuel from the wing locker tanks can be utilized. This fuel is not directly available to the engines. It can only be transferred by electric pumps to the main tanks. By the time the fuel from the wing locker tanks is fully transferred the mains are full once again and all other tanks are now near-empty."


Does this sound about right?

Feel free to give any advice/tips about the B model
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Old 05-13-2010, 08:12 AM   #2 (permalink)
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yes.

Take off and land on mains(tips).

Fly the first hour on the mains(to make room for "return" aux fuel).

Then the next hour on the aux's to your/bosses comfort level.

Then at least half an hour or so on the mains again to make room for locker fuel.

Transfer the locker fuel(pumped rather than fed). Watch for L or R Trans light. While remaining on mains, of course.

Might want to empty wing lockers first in rotation, though.

Land nice, the B doesn't have trailing ling gear like the C.
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Old 05-13-2010, 08:44 AM   #3 (permalink)
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"Pumps on high, gas on the mains"

No matter how many triggers you set to remember, if you fly it often enough, you will forget and run an aux tank dry.
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Old 05-13-2010, 09:38 AM   #4 (permalink)
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If the fuel pump system has been modified per MEB88-3 leave the pumps off
(except for emergency) and save them for when you need them. They cost about $1500.

If it hasn't been modified, don't forget to reset the fuel pumps after a fuel starvation event. The pumps would have switched to high output and when the throttles are reduced for landing the engines will flood and quit.

That will not impress the boss or CFR at the airport.

Fly Safe.

Pat
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Old 05-14-2010, 05:08 PM   #5 (permalink)
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Thanks for all the information... In real life, it doesn't seem to be thaat bad...just as they say 'a thinking pilot's airplane' to put it politely. The tip tanks seem to give a bit more stability than the C
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Old 05-20-2010, 07:43 AM   #6 (permalink)
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It's basically the same system in teh C310's I flew. We'd go 90 minutes on the mains before draining the AUX tanks. This is even better, we had the nacelle tanks, but it was only on one side, so then you had to cross-feed to balance the load. Royal pain in the rear, but it was another 20 gallons you sometimes really wanted on board.

If you run the AUX's too early, you can over-fill the tanks and you'll basically just vent the fuel out, which does no one any good, and same thing with the nacelles. Overall, it's not as bad as one might assume, it'll just become second nature after awhile. Of course, when I was flying freight, we'd run the Aux's dry just to maximize our fuel usage, but not necessarily a good idea with Pax.
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Old 06-16-2010, 07:52 PM   #7 (permalink)
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Quote:
Originally Posted by Ewfflyer View Post
It's basically the same system in teh C310's I flew. We'd go 90 minutes on the mains before draining the AUX tanks. This is even better, we had the nacelle tanks, but it was only on one side, so then you had to cross-feed to balance the load. Royal pain in the rear, but it was another 20 gallons you sometimes really wanted on board.

If you run the AUX's too early, you can over-fill the tanks and you'll basically just vent the fuel out, which does no one any good, and same thing with the nacelles. Overall, it's not as bad as one might assume, it'll just become second nature after awhile. Of course, when I was flying freight, we'd run the Aux's dry just to maximize our fuel usage, but not necessarily a good idea with Pax.
Exactly... one odd thing is that the main (tip) tank electric fuel pumps are wired through the landing lights - the airplane I flew/fly actually had one of the landing lights disconnected - which, of course disconnected the electric fuel pump.
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