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 Post subject: 421C Aux Pumps
PostPosted: 18 Jul 2018, 23:47 
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Joined: 04/28/16
Posts: 26
Company: Herndon Aviation
Aircraft: A36TC, 421C
I just bought a 421C, and have just started getting into the flight levels with it. (Still have my Bo though... :)
I know there are several 421 pilots on here, so I thought I’d see what you guys think. When I shut my aux pumps off in the flight levels, my engines get starved for fuel. As in they’d die if I didn’t turn the pumps back on...
The POH says pumps on “as necessary”. Have any of you other 421 guys experienced this? Doesn’t seem normal...
The POH does say to leave them on for 5 minutes to reduce vapor tendencies before shutting off. I am planning on trying this tomorrow.


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 Post subject: Re: 421C Aux Pumps
PostPosted: 19 Jul 2018, 03:38 
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Joined: 05/31/13
Posts: 1227
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Company: Docking Drawer
Location: KCCR
Aircraft: C425
I used to have a twin commander with TIO540's and whenever I flew it high I had to leave the aux pumps on for 15-20 minutes after reaching altitude otherwise I would get unstable fuel pressures. My theory was that after some time the fuel cooled enough that it reduced the vapor lock tendency and the engine driven pumps worked OK. But you have a different engine and it sounds like a more severe problem. I'm sure someone here can chime in with a better answer.

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 Post subject: Re: 421C Aux Pumps
PostPosted: 19 Jul 2018, 04:13 
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Joined: 02/17/10
Posts: 600
Post Likes: +822
Company: JCrane, Inc.
Location: KVES
Aircraft: C441, RV7A
The aux pumps are req’d to be on low for take-off and landing, only for the potential of engine driven pump failure. Many operators run the aux pumps on low for the entire flight. I don’t, because 1) I’ve never had a vapor lock issue, & 2) running the aux pumps all the time would mask the failure of the engine driven pump.
If you need to run the aux pumps to avoid vapor lock, that’s fine, but turn them off briefly at least once each flight to fonfirm the engine driven pump is still performing.
Enjoy the 421!

Gary S


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 Post subject: Re: 421C Aux Pumps
PostPosted: 19 Jul 2018, 07:03 
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Joined: 02/09/09
Posts: 5551
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Location: Owosso, MI (KRNP)
Aircraft: 1969 Bonanza V35A
I operated a 421C for about four years (and most other Twin Cessna's for many years) and we would run the aux pumps enroute for the very reason you specify. The problem was much more pronounced after a long climb (i.e., hot engine compartment) and especially when the fuel temperature started warm (i.e., heat soaked wings or fuel truck). During the colder months, we had no problem and I would turn them off after a few minutes in cruise. There many others that seemed to do the same based on my reading in the Twin Cessna Forum.

Another important tip is to always run IPA or an anti-icing inhibitor in the fuel. You can get icing in the flow dividers on the top of the engines, and in the 421C/414A/404. Google John and Martha King's C-340 for more info...

Also, the fuel crossflow lines are the lowest point in the fuel system in the above listed airplanes, which is where any water will accumulate, then quickly freezes enroute leaving crossflow useless (i.e., do you have one locker tank?). Run the crossflow once a week to suck most water out, but running an anti-icing inhibitor will help prevent an unpleasant surprise, especially if your depending on it..

I usually ran a quart of IPA in each tank during fill up at home. We have self serve fuel at home and I bought a sports bottle rack with quart bottles from Amazon and filled them. Then I mixed them in the fuel stream when fueling.. I have a 55 gallon drum in the hangar which has lasted over four years with the 421 and a few other airplanes.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

Jason


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 Post subject: Re: 421C Aux Pumps
PostPosted: 19 Jul 2018, 08:43 
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Joined: 01/29/14
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My 421 does the same on hot days. After 10 mins in cruise I can turn them off with no problems.

Though on one of my engines ff goes up slightly when the pump is turned off.

Enjoy the 421 - they really are a wonderful travelling machine.


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 Post subject: Re: 421C Aux Pumps
PostPosted: 20 Jul 2018, 08:59 
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Joined: 04/28/16
Posts: 26
Company: Herndon Aviation
Aircraft: A36TC, 421C
I discovered that mine is just the same as others... If I wait long enough, it does just fine. Mine is longer than 10 minutes, but it does work.
The good news is that the pumps can sustain pressure in the flight levels! Just part of the learning curve for me.

Thanks for your input!


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 Post subject: Re: 421C Aux Pumps
PostPosted: 17 Sep 2018, 17:22 
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Joined: 10/15/15
Posts: 70
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Location: EDDS
Aircraft: C510
Username Protected wrote:
The aux pumps are req’d to be on low for take-off and landing, only for the potential of engine driven pump failure. Many operators run the aux pumps on low for the entire flight. I don’t, because 1) I’ve never had a vapor lock issue, & 2) running the aux pumps all the time would mask the failure of the engine driven pump.

If the engine driven fuel pump fails, an aux pump at low won‘t help. It needs to be on high. You put it on low for T/O and LDG only to ensure best fuel supply (vapor, dirt, ...).


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 Post subject: Re: 421C Aux Pumps
PostPosted: 17 Sep 2018, 17:27 
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Location: EDDS
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Username Protected wrote:
Another important tip is to always run IPA or an anti-icing inhibitor in the fuel. You can get icing in the flow dividers on the top of the engines, and in the 421C/414A/404. Google John and Martha King's C-340 for more info...

That‘s why Cessna came up with the heated fuel manifolds. The trailing link gear C421Cs (1980 and on) have them and they were available as retrofit kit. I installed them in my 1977 C421C. No more IPA or Prist (DIEGME) necessary.


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 Post subject: Re: 421C Aux Pumps
PostPosted: 18 Sep 2018, 06:17 
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Joined: 03/09/13
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Location: Byron Bay,NSW Australia
Aircraft: CE525,PA31
Username Protected wrote:
If the engine driven fuel pump fails, an aux pump at low won‘t help. It needs to be on high. You put it on low for T/O and LDG only to ensure best fuel supply (vapor, dirt, ...).


Not sure if that is correct if you fly LOP I was told that with a TSIO520 and lost an engine driven fuel pump I’m cruise and was able to maintain operations with pump on low LOP.

Andrew


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 Post subject: Re: 421C Aux Pumps
PostPosted: 18 Sep 2018, 09:06 
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Joined: 12/29/10
Posts: 2528
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Location: Dallas, TX (KADS & KJWY)
Aircraft: T28B,7GCBC,E90
For whatever it's worth...

I flip the boost pumps on when I enter the runway, and off when I exit. I run them all the time in 'low' mode. Why? I honestly don't know - I was trained that way and it seems to work, so I haven't messed with it in +1,000hrs of 421 time!

I've also never added IPA/prist and have never had an icing issue.

As always, YMMV. Just one guy's experience.

Robert


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 Post subject: Re: 421C Aux Pumps
PostPosted: 18 Sep 2018, 17:45 
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Joined: 02/09/09
Posts: 5551
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Location: Owosso, MI (KRNP)
Aircraft: 1969 Bonanza V35A
Username Protected wrote:
For whatever it's worth...

I flip the boost pumps on when I enter the runway, and off when I exit. I run them all the time in 'low' mode. Why? I honestly don't know - I was trained that way and it seems to work, so I haven't messed with it in +1,000hrs of 421 time!

I've also never added IPA/prist and have never had an icing issue.

As always, YMMV. Just one guy's experience.

Robert


The 421C (and 402C, 404 and 414A) crossfeed lines will freeze after an hour or so at altitude. Water sits in them since they are the lowest point in the system, and has no drain in the center of the fuselage. Then, when you need to crossfeed, they will not as the line is frozen. Even a hangared airplane accumulates some water in the system...

When I flew boxes in the 402C and 404, we could crossfeed for a few minutes weekly and it would help this issue. The 421C, I crossfed every leg without passengers. It sure scares the hell out of everyone when you need the fuel from the aux tank (via the left main) and the right engine quits.... IPA/Prist will prevent this water from freezing if added at sufficient rates. I usually added one quart when filling up at home..

Jason


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 Post subject: Re: 421C Aux Pumps
PostPosted: 18 Sep 2018, 18:40 
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Joined: 12/29/10
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Location: Dallas, TX (KADS & KJWY)
Aircraft: T28B,7GCBC,E90
Username Protected wrote:

The 421C (and 402C, 404 and 414A) crossfeed lines will freeze after an hour or so at altitude.


Thanks Jason - I get the theory, just it's not something that has ever happened to me when cross-feeding.

Robert


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 Post subject: Re: 421C Aux Pumps
PostPosted: 18 Sep 2018, 21:24 
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Joined: 02/09/09
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Location: Owosso, MI (KRNP)
Aircraft: 1969 Bonanza V35A
Username Protected wrote:

The 421C (and 402C, 404 and 414A) crossfeed lines will freeze after an hour or so at altitude.


Thanks Jason - I get the theory, just it's not something that has ever happened to me when cross-feeding.

Robert


Either your lucky, or your never operating at high enough altitudes in Texas for the water to freeze..

Jason

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 Post subject: Re: 421C Aux Pumps
PostPosted: 19 Sep 2018, 08:56 
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Joined: 12/29/10
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Location: Dallas, TX (KADS & KJWY)
Aircraft: T28B,7GCBC,E90
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Either your lucky, or your never operating at high enough altitudes in Texas for the water to freeze..

Jason


Lucky and a well maintained bird. I may live in Texas, but I have a 421 so I can leave Texas (not at all a bash on Texas!). Never had a flight at 220 that wasn't well below freezing...

The use of IPA/Prist is not universal across the fleet. Some operators swear by it, some never use it. Like most things in aviation, "it depends".

Robert


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 Post subject: Re: 421C Aux Pumps
PostPosted: 19 Sep 2018, 14:15 
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Joined: 02/09/09
Posts: 5551
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Location: Owosso, MI (KRNP)
Aircraft: 1969 Bonanza V35A
Well, good luck... Well maintenance has nothing to do with it. All fuel has some water in it. It was just a bad design of the wet wing Twin Cessna's. I've seen it in just about every 402C/404 and 421C that I've flown, and they were operated from different airports, different fuelers, and different operators...

if you fly it enough at altitude, and cross feed often if you have one aux tank, you'll remember this post one day. Hopefully, yours has the fuel heaters. John and Martha King can explain what can happen if not...

Jason


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