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AFP boost pump use

erich weaver

Well Known Member
I have an IO-360B1B with AFP boost pump and am nearly at the point where I can start her up for the first time.

My dumb-*** question of the month: How is the boost pump properly used? That is, when should it be turned on and when should I turn it off?

Dont tell anyone I asked this.

erich
 

Not a dumb question and I'll tell no one I know!

Here is a good thread on the subject.

My personal usage is as follows:
- about 5 secs while 'priming' a cold engine (throttle and mixture full open)
- all takeoffs and landings
- flight below 2500' AGL

Hope this helps.
 
I only use it for priming and emergencies. But that's just me. I totally understand if others want to use it for T/O and landing. I just prefer not to.

Karl
 
RV8N said:
I only use it for priming and emergencies. But that's just me. I totally understand if others want to use it for T/O and landing. I just prefer not to.
If you ever find yourself needing to take off on a 105F+ day with a heat-soaked engine, you might think otherwise about your current M.O.

When you talk about "preferring" not to, your engine-driven fuel pump "prefers" not to suck fuel and would gladly suck vapor if the conditions are right. That could really ruin your day.

Running the boost pump on takeoff and landing is cheap insurance imho.
 
fuel pump

I use mine to prime and start, to take off and land, when I'm in a slow speed fight with Hide, and when I'm switching fuel tanks. There is some boost pump noise when taxiing so I turn it off (good check on engine driven pump) to taxi to runway and I turn it off immediately after landing. It is also used to pressuize the fuel system to drain the gascolater. Have fun
 
dan said:
Running the boost pump on takeoff and landing is cheap insurance imho.

Maybe....but maybe not Dan. I used to fly a Piper Archer (carbie) and the POH called for boost pump on for take off and landing. That seemed reasonable to me and I concluded that every plane would require having the boost pump on for take off and landing. However it is definitely not the case.

I bought into a Cessna 182S (fuel injected) recently and noted that the POH specifically calls for NO boost pump on during take off and landing. Apparently there have been cases where using the boost pump has caused the mix to go ultra rich and affect engine performance. On some planes using the boost pump in flight can actually cause the engine to quit for this same reason (ie. it's for mechanical fuel pump failure or vapourisation problems only).

Some people suggested to me that perhaps Cessna does not require the boost because the engine might run even if the mechanical pump fails due to the high wing and fuel head. I contacted Cessna about this and they confirmed that if the mechanical pump fails and the boost is not on....the engine will definitely quit. However their recommendation is to switch on the boost pump in flight only when there is an indication of engine power loss.

I think this is not a black and white matter. I think it varies with the boost pump/ mechanical pump /FI servo /engine combination. And the problem here is that RV builders tend to have a lot of different combinations of these.

My inclination would be to NOT have the boost on for take-off and landing until some-one with acknowledged technical authority suggests otherwise for my specific fuel system combination.
 
Bob, in both cases you're talking about a carb (low pressure needs), not FI (high pressure needs). And in the 2nd case you're talking about a high wing. Apples and oranges.

If you have a low wing and fuel injection, just do us all a favor (I like my friends much better when they're alive) and at least run your electric boost pump on takeoff.
 
dan said:
Bob, in both cases you're talking about a carb (low pressure needs), not FI (high pressure needs). And in the 2nd case you're talking about a high wing. Apples and oranges.

If you have a low wing and fuel injection, just do us all a favor (I like my friends much better when they're alive) and at least run your electric boost pump on takeoff.


Sorry Dan there's some confusion here. I specifically stated that the C182S is fuel injected. This is a high pressure fuel system but the POH specifically calls for the boost pump being OFF on take-off and landing. It's the same for a number of fuel injected aircraft including some with low wings. There are intrinsic dangers in running the boost pump in flight on some fuel injection combinations...it's a fact.

Now intuitively I favour the notion of having the boost on for take-off and landing (as I'm sure many others do) but I suspect this is another case in aviation where intuition and science may not coincide.
 
Captain Avgas said:
Sorry Dan there's some confusion here. I specifically stated that the C182S is fuel injected. This is a high pressure fuel system but the POH specifically calls for the boost pump being OFF on take-off and landing. It's the same for a number of fuel injected aircraft including some with low wings. There are intrinsic dangers in running the boost pump in flight on some fuel injection combinations...it's a fact.

Now intuitively I favour the notion of having the boost on for take-off and landing (as I'm sure many others do) but I suspect this is another case in aviation where intuition and science may not coincide.
Ah...you did, and I missed that. Only reason I can think of for leaving the pump off (and I'm talking about an injected Lycoming with, say, traditional FI systems such as Bendix/Precision or AFP injection) would be to increase longevity calendar-time-wise of the pump. A good reason but not good enough for me!
 
Actually, you will find most all Continental fuel injections systems will want the boost pump on only for priming and failure of the engine driven pump. The servo system is very sensitive to input pressure and will often over-richen the mixture if both pumps are working.

On the other hand, the Bendix (Silverhawk, AFP) system used on most Lycomings is quite happy with both pumps working.

I believe turning on the boost pump for Lycomings with the Bendix type FI system is prudent and is recommended by most of the certified POH's I have seen. Diagnosing a engine pump failure on takeoff would be a real challenge...

Deene Ogden
EAA Tech Counselor and Flight Advisor
CFII, CFIG, MEI
 
There is a good reason for running it t/o and landing and low altitude. There have been mechanical fuel pump failures, and there is an AD for them as a result. Ask me how I know. Article on the failure here

Enjoy,
 
What does Lycoming recommend?

The answer is located on page 53 in the Key Reprints.
http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key Operations.pdf

"Use of Fuel Boost Pumps with Lycoming Engines

As an engine manufacturer, we are frequently asked about the proper use of the fuel boost pump with our power plants. Although we can?t pretend to be an expert on the fuel boost pump itself, we have some positive recommendations concerning its use with our engines. Where a boost pump is provided by the airframe manufacturer, and the airframe Pilot?s Operating Handbook has a limited treatment of the use of the fuel boost pump, perhaps this discussion can provide the necessary fuel boost pump information for the pilot in order to operate his or her
engine as safely as possible.

It is necessary to supply the engine with a steady, uninterrupted flow of fuel for all operating conditions. Entrapped air, temperature
changes, pressure drops, agitation in the fuel lines and other factors affect the release of air and vapor from the fuel system. Under some circumstances where an engine-mounted fuel pump is provided, it may not be able to pump a continuous fuel supply free of excessive vapor.

An effective continuous fuel supply is provided by use of the fuel boost pump. As a general recommendation, the fuel boost pump should be used with Lycoming engines in all conditions where there is any possibility of excessive vapor formation, or when a temporary cessation of fuel flow would introduce undesirable hazards. The conditions under which Lycoming recommends operation of the fuel boost pump are as follows:

1. Every takeoff.
2. Climb after takeoff unless Pilot?s Operating Handbook says it is not necessary.
3. When switching fuel selectors from one separate fuel tank to another, the fuel boost pump should be ?on? in the new tank until the operator is assured there will be no interruption of the fuel flow.
4. Every landing approach.
5. Any time the fuel pressure is fluctuating, and the engine is affected by the fluctuation.
6. Hot weather, hot engine ground operation where fuel vapor problems cause erratic engine operation.
7. Some General Aviation aircraft require the use of the fuel boost pump during high-altitude flight. This will be spelled out in the Pilot?s Operating Handbook.
8. If the engine-mounted fuel pump fails.

If the fuel boost pump is used during ground operation, don?t fail to check the condition of the engine-mounted fuel pump before takeoff by turning the boost pump off briefly, and then back ?on? for takeoff. If the engine-mounted pump has failed, it would be safer to know that on the ground rather than in the air when the fuel boost pump is turned ?off.?
When in doubt, do the safest thing and use the fuel boost pump with Lycoming engines. Don?t be ?stingy? with the boost pump. In most cases, they last the overhaul life of the engine, and are then exchanged or overhauled themselves. AS A REMINDER, the airframe Pilot?s Operating Handbook is the authority if boost pump information is spelled out in it."
 
Hummmm....

RV6_flyer said:
What does Lycoming recommend?

The answer is located on page 53 in the Key Reprints.
http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key Operations.pdf

"3. When switching fuel selectors from one separate fuel tank to another, the fuel boost pump should be ?on? in the new tank until the operator is assured there will be no interruption of the fuel flow.

If the fuel boost pump is used during ground operation, don?t fail to check the condition of the engine-mounted fuel pump before takeoff by turning the boost pump off briefly, and then back ?on? for takeoff. If the engine-mounted pump has failed, it would be safer to know that on the ground rather than in the air when the fuel boost pump is turned ?off.?
"

I was told (I can remember who) that I should turn on the pump in my RV before switching tanks. This seemed a little strange, but I tried to remember to do it. But now I am thinking that sense the pump is down stream of the selector valve that during the switch the pump could be creating a vacuum on the fuel that is between the pump and the selector during the switch over. I know this is not a long period of time, but what is gained by turning on the pump for the switch?

Kent
 
Curious that Cessna would say no boost pump. AFAIK, that's a Bendix-style system on the 182S and it should not be sensitive to high fuel-inlet pressure, just as the AFS or Silverhawk systems are not. Maybe Cessna is trying to cut down on warranty claims on the pumps...

Anyway, I always run the boost pump with an IO-390/AFS setup for takeoff, the initial climb during hot weather, and landing. I don't generally turn it on for switching tanks, but I've high-winger with a reasonable amount of head pressure.

Seems a no-brainer to me.

MC
 
RV6_flyer said:
What does Lycoming recommend? SNIP


Gary, for this discussion, perhaps we should be interested not in what Lycoming says, but what the FI system manufacturer says. Since builders might use all kinds of various systems for FI, the design of the fuel system and controller should drive decisions on whether or not the boost pump should be used.

I was surprised when I first learned that some FI systems may operate improperly when the boost pump is on (a friend's Bonanza comes to mind).

I for one have the boost pump on during all takeoff/landings (mine is AFP). I would not install a FI controller which doesn't tolerate having the boost pump on.
 
kentb said:
I was told (I can remember who) that I should turn on the pump in my RV before switching tanks. This seemed a little strange, but I tried to remember to do it. But now I am thinking that sense the pump is down stream of the selector valve that during the switch the pump could be creating a vacuum on the fuel that is between the pump and the selector during the switch over. I know this is not a long period of time, but what is gained by turning on the pump for the switch?

Kent
Here's what is gained...

Let's look at an extreme case as an example. I decide to switch tanks. I don't turn the boost pump on. Let's say I reaaaaaaallllly slooooowwwly move the selector valve. With most selector valves that I'm aware of, there will be a point, somewhere in the middle of the transition (gee, probably right smack dab in the middle) where flow is either blocked completely, or at least blocked partially (i.e. a slight amount of fuel may be allowed to flow from "both" sources...unlikely but conceivable depending on the valve design). At a minimum, flow is restricted, and in all likelihood it's blocked.

Ok, so in this case the engine driven pump is sucking away at that blocked source of fuel. Pressure on the valve/tank side of the engine driven pump is going to drop pretty quickly, right? To me that spells the potential for vapor lock, especially if the components up by the engine are hot.

So what is gained by running the boost pump in this scenario? My interpretation of what's going on is that the "onus" is now shifted to the electric boost pump to suck fuel from the restricted or blocked source, but the likelihood of pressure dropping at the engine driven fuel pump's inlet is drastically reduced. The likelihood of vapor lock developing at the engine driven pump's inlet is nearly eliminated...unless of course the selector switch is left, say, OFF for some extended period of time...and in that pathological case you're screwed regardless.

Think about what the GOALS are in general. Whether you're in a volatile phase of flight such as takeoff or landing, or whether you're switching fuel tanks, the goals (at least in my mind) are:

1. Provide a relatively constant, definitely sufficient quantity of fuel to the engine for it to continue running uneventfully.
2. Avoid vapor lock, which would severely impact #1.

That's it! You can't convince me that on a Lycoming with Bendix/Precision/AFP, running the electric boost pump does NOT help ensure #1 and #2.

Sure, my example was pathological...a really SLOW movement of the selector valve. And that might be the extreme case...but every time you switch tanks there is a momentary POTENTIAL, albeit brief, for the development of vapor lock. Granted, most fuel tank selector valve changes happen at altitude, and you should have plenty of time to resolve the issue if something does happen...but why put yourself in the position where it CAN happen?

As for takeoff, it's the same thing in my mind. I want to stack the deck as much in my favor as humanly possible. If my engine driven pump decides to fail -- or perhaps somewhat more likely, if a vapor lock condition becomes imminent, I don't want to have to do ANYTHING to resolve it. Think about the "time lost" factor here, where you have to (a) determine something is wrong, (b) determine what is wrong, (c) react. Why would you possibly put yourself in a situation where, right after takeoff and your engine is coughing, you would DENY yourself precious seconds while your airplane is a glider? I for one would much rather "discover" the failed engine driven pump at, say, 1000' AGL when I flip the boost pump off. I feel the deck is stacked much more in my favor with altitude BELOW me.

I know I'm preaching mostly to the choir here, but there are some people who don't agree with this, and I encourage them to look objectively at the possibilities. Do you always fly a low-and-slow final approach to land? Do you always touch down halfway down the runway? Do you always cruise at 20' AGL? Do you never use the boost pump on takeoff?
 
Last edited:
KPmarc said:
Curious that Cessna would say no boost pump. MC

Gravity??? Lot more reliable than a pump.

My Stinson has NO fuel pump at all, of course it also is a carb.

Mike
 
Not nearly enough head pressure to keep the servo working should the engine-driven pump die.
 
RV6_flyer said:
What does Lycoming recommend?

Lycoming recommends that "The airframe POH is the authority if boost pump info is spelled out in it". That stands to reason because Lycoming produces only the engine and the airframe manufacturer establishes the total fuel system/engine configuration.

In the case of the fuel injected Cessna 182, 206 and 210 the POH calls for no boost on take-off and landing.

Now an uninquisitive person might dismiss this recommendation outright as a load of rubbish....but a smarter person might be inclined to wonder why a company that has built more GA aircraft than any other in history (and might know a thing or two) would take this stance.

If people think this is because these are high wing designs they are mistaken. In fact these systems require a fuel system pressure around 14 psi and the fuel head from the wings can not generate more than 1 psi. In other words the engine will quit if the mechanical pump fails on the fuel injected Cessnas.

The low wing Beechcraft Bonanza and Baron are the same....but even more critical. In these planes it can be deadly to use the boost pump in flight. At low power settings (eg approach) the boost can snuff out the engine. A number of people have died because of this. The POH spells it out.

In particular the Continental 470 and 520 have been particularly susceptible to loss of power because using the boost pump in flight can cause the engine to run ultra rich.

However the engine in the fuel injected Cessna 182S and 182T (current model) is the Lycoming IO540....but the POH is quite clear about not using boost on take-off and landing. It states that the boost pump should only be switched on if the engine falters.

NOW READ THIS: I am not saying that RV builders should not use their boost pump on take-off and landing. What I am saying is that the advisability of doing so will depend upon the total fuel system/engine configuration. That means the type of filters, boost pump, gascolator (if installed), mechanical pump, servo unit, and engine.

There's a bigger picture here and I'm just trying to bring some information to the table that might be of interest. I'm NOT interested in an argument in whether the use of boost in flight is right or wrong. Clearly it is right for some fuel systems and not right for others.

Because every RV builder is fabricating a potentially unique aircraft they will have to do the reseach to ascertain what is best for their particular fuel configuration. Note that I said "research"...not "intuition".

Cheers Bob
 
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