Aux fuel pump on or off for take off?

[Contacttower]

I've always understood that one switches on the aux fuel pump for take off so that in the event of the engine driven pump failing one still gets fuel to the engine.

Now I notice that on Cessnas and other high wing aircraft the aux pump is usually not selected on for take off. I had always assumed that this was because the fuel in the tanks would reach the engine by gravity in the event of engine fuel pump failure, ensuring that the engine did not fail if the engine driven pump did. Looking in the C182 POH however revealed no such reassurance, stating:

"It is not necessary to operate the auxiliary fuel pump during normal take off and landing, since gravity and the engine driven fuel pump will supply adequate fuel flow. In the event of failure of the engine driven fuel pump, use of the auxiliary fuel pump will provide sufficient fuel to maintain flight at maximum continuous power."

That seems to imply that gravity alone will not be enough to keep the engine running...so why not have it on for take off and landing? Can anyone clarify this for me?

[SkyHawk-N]

That seems to imply that gravity alone will not be enough to keep the engine running

I hope gravity is enough, my 172 doesn't have a fuel pump at all. ;)

I assume that the extra pressure from a fuel pump is required for the fuel injection system to vaporise the fuel?

[IO540]

On my TB20, one has the aux pump on for arrival and departure but there is no evidence that it does anything useful whatsoever.

Until the engine driven pump fails ;)

[mixsfour]

No aux pump on C152 either.

[Contacttower]

I assume that the extra pressure from a fuel pump is required for the fuel injection system to vaporise the fuel?

I'm not sure, having flown the older carb C172 and C152 I was aware that they don't have fuel pumps, but the injected C182 I currently fly does...basically what I'm asking is what happens if the engine pump quits, will the engine still run?

The engine failure checklist also implies that the engine won't run without the aux pump since it says to put it on and leave it on if engine pump failure is suspected.

[FlyingStone]

On during takeoff and landing (I usually turn it off after retracting flaps and reaching about 500ft AGL), since not many people have the excess brain capability to diagnose engine problems at 100ft after takeoff/go-around. It would be such a shame to not use redundancy during critical phases of flight, if you have it available. The gravity fed fuel system should provide sufficient fuel pressure for takeoff power without assist from auxiliary fuel pump, but are you willing to bet your life on it?

I cannot see any downside of using auxiliary fuel pump (low-speed for engines equipped with two-speed fuel pumps) during any phase of flight (running it during cruise without any specific reason seems a bit contraproductive though), but there are quite a pros.

[IO540]

Some of the electric pumps have eye watering prices (well into 4 digits) so running them pointlessly is pointless.

[Contacttower]

On during takeoff and landing (I usually turn it off after retracting flaps and reaching about 500ft AGL), since not many people have the excess brain capability to diagnose engine problems at 100ft after takeoff/go-around.

What sort of aircraft is that? I would tend to agree with your statement, I'm just left wondering why Cessna (with reference to the 182) do not think it necessary to do so...

[Speedbird48]

I have a 172Rg with a carburetor and an electric fuel pump. The only time it is used is prior to start, and for engine failure in flight, if fuel pressure is below 0.5psi.

So extra pressure for injection is not necessarily so. The difference between a normal 172 or 182 is that my carburetor is on the back, as is the 182RG, and not underneath the engine.

Speedbird 48.

[A and C]

Some aircraft need the Aux pump and on others it will stop the engine due to a "rich cut" so this is not a topic for the pprune opinions, all you have to do is:-

Read the flight manual!

[SNS3Guppy]

I cannot see any downside of using auxiliary fuel pump (low-speed for engines equipped with two-speed fuel pumps) during any phase of flight (running it during cruise without any specific reason seems a bit contraproductive though), but there are quite a pros.

Know your aircraft.

Failure to use the auxilliary pump in some aircraft can result in engine failure. Use of the aux pump in other aircraft can cause an engine failure. Know the difference.

[Contacttower]

There's no need to shout A and C. :) As my first post clearly states I have read the POH, (never quite been sure what the technical difference between the POH and the Flight Manual is but in this case it is the same thing) and found it ambiguous on its reasoning.

[Big Pistons Forever]

I've always understood that one switches on the aux fuel pump for take off so that in the event of the engine driven pump failing one still gets fuel to the engine.

Now I notice that on Cessnas and other high wing aircraft the aux pump is usually not selected on for take off. I had always assumed that this was because the fuel in the tanks would reach the engine by gravity in the event of engine fuel pump failure, ensuring that the engine did not fail if the engine driven pump did. Looking in the C182 POH however revealed no such reassurance, stating:

"It is not necessary to operate the auxiliary fuel pump during normal take off and landing, since gravity and the engine driven fuel pump will supply adequate fuel flow. In the event of failure of the engine driven fuel pump, use of the auxiliary fuel pump will provide sufficient fuel to maintain flight at maximum continuous power."

That seems to imply that gravity alone will not be enough to keep the engine running...so why not have it on for take off and landing? Can anyone clarify this for me?

You did not specify which model of C182, which is important to answer your question as there are 5 different possible engines from either Continental or Lycoming depending on the model, some are carburated and some are fuel injected and there are turbocharged version of both variants. The Lycoming carburated versions do not have a fuel pump but do have a aux pump while the have fuel injected versions both engine driven and aux pumps and the Continentals have neither. When and how to use the aux pump is model specific and therefore in lieu of the flight school one size fits all approach to dumbing down aircraft operation, which you can get away in simple airplanes, it is important to follow the POH instructions in more complex aircraft; as there may be significant differences even within the same aircraft type depending on the year built and the engine fitted.

With respect to your question (highlighted in red). The note doesn't say the engine will stop if the engine driven pump fails it simply notes that the aux pump will provide all the fuel the engine needs at full power if required.
If operation of the engine driven pump was required to keep the engine running under normal circumstances then its operations would be required in the POH takeoff procedures in the normal operation section and there would be a cockpit placard. If the the engine fuel pump failed and the engine started to lose power than use of the pump would be indicated.

[Pilot DAR]

Yes, you tell'm A&C, read the Flight Manual!

If it is vague, that's unfortunate, but happens. It probably means you could get it wrong, and it would not be the end of the flight.

Failure to read the Flight Manual, and comply, were it says to, can have you gliding. When I flew the C 310, it was pumps on low for landing. I borrowed a friend's C 210 in California. I figured it had an IO-520 too, so I tried the same thing. Nope, it quit when I selected low pump (hands moving really fast for a few seconds). It was quite happy no pump (I don't think I ever did read the flight manual for that plane.)

If in doubt, I do not run it. Expensive when it quits, and I don't want to bring that about sooner than need be. If the engine runs rough, I'll put it on.

Oh, and POH/Owners's Manual/Flight Manual...

Back in the day, the manufacturer published what they wanted to (sometimes none - simple placards med the requirement). Though the term "Flight Manual" appears in the design requirements as far back as 1949, it was not actually required for aircraft less than 6000 pounds until 1978 (there were some variations on this in the interm, but this is generally the rule). So all manner of non required publications, and varied formats accompanied aircraft. In some cases, there was both an FAA approved Flight Manual, and a Pilot's Handbook! This creates real confusion, when you don't know which to believe! (in the case of the PA-30, believe the typewriter created Flight Manual, not the spiffy POH!)

At the amendment of FAR Part 23, ammendment 21 of 1978, the Flight Manual, with a specified format became an actual requirement for the aircraft, meaning that the design would not be approved without it. That flight manual is law, and will not be confused with other similar documents from the manufacturer.

That said, aircraft could still be made after 1978, without requiring a Flight Manual, because they were still made to the old cert basis...

Clear? No, I thought not!

[SNS3Guppy]

The aircraft flight manual for the Cessna 210 (and 206 and 207) will provide a procedure for fuel flow fluctuations which, if followed, can cause an engine failure, or prevent a restart.

Use of the boost pump at the wrong time can have dire consequences. The Cessna manual places use of the boost pump first, when switching tanks is often all that's needed. Knowing the fuel system makes all the difference in the world. Whereas Cessna dictates supplying boost first, the result is an increase in hot bypass fuel returned to the fuel kidney sumps, and an increase in return vapor up the feed line to the tank. The result is a fuel stoppage and no way to restore flow until tanks are switched. If the boost is applied before switching tanks, one can cause the same problem in the second kidney sump, and eliminate all fuel sources as usable.

Instead, by leaving the boost off, switching tanks, retarding the throttle, and adjusting mixture, then one can boost to one's hearts content, and be happy.

Know the aircraft flight manual procedures, know the system, and know why one is applying the boost in the first place.

[A and C]

The shouting is for one simple reason and that is with some engines putting the aux pump on will stop the engine.

What I don't want to see is some poor unfortunate kill themself (and others) by taking advice from this forum.

As some of the advice is good for some engines the only way to know what to do for the aircraft that you are flying is to Read the flight manual.

The aux pump is installed on some aircraft in case of engine driven pump failure and if it is used when the engine driven pump is working it will overfuel the engine resulting in the engine running over rich and there is a good chance it will stop.

[Jan Olieslagers]

Hadn't I always understood the main purpose of an auxiliary fuel pump is to counter vapour-locking? Apart from the redundancy, that is.

[englishal]

I believe that using the Aux FP otherwise in accordance with the flight manual can lead to bubbles forming in the fuel and associated problems. I can't remember whether that is ON when it should be OFF or OFF when it should be on! Our plane POH say ON for the climb, regardless of altitude, so even climbing through FL195 the Aux pump should be ON....

[Contacttower]

The shouting is for one simple reason and that is with some engines putting the aux pump on will stop the engine.

While I appreciate your concern I think I'm capable of digesting the information offered on here, comparing it with the Flight Manual and making a reasonable judgement about whether to follow it or not.

As it happens, in the case of the Lycoming Model IO-540-AB1A5 6 cylinder injected engined (apologies for not posting the engine model originally) it is OK to operate the aux pump continuously as it results in only a very small enrichment of the mixture, in fact in conditions conducive to fuel vapor formation its use is recommended during flight. Now I already new all that and it doesn't answer my question...:confused:

[2high2fastagain]

ContactTower has a fair point. In the TR182 POH for example, it says that if the engine driven fuel pump fails, then gravity flow will provide sufficient fuel flow for level or descending flight. It suggests that if the fuel pressure drops to 0.5psi (or 3.0psi for some serial numbers or service kit mods), then the aux pump should be turned on. For this aircraft type at least there don't seem to be any warnings which would preclude you using it for take-off and there is a case to say that it would probably help if you had an EFATO due to fuel pump failure in at Vx climb. That said, I fly mine by the POH. At least that minimises possible undesirable, unforeseen knock-on effects as are being discussed. I follow the POH and listen to my engineer. I've seen a couple of friends screw their engines when they've searched for the holy grail of lean of peak with their engine monitors and I don't want to go there.

[Jan Olieslagers]

Silvaire,
Surely it is a good thing to know the plane and its systems, and of course we all should consult the doc. I do will remember though that not all documentation is to be blindly trusted, not even if it comes from a trusted source like the plane manufacturer (if you trust their plane, you do trust their writings, too?)
Out of sheer curiosity, really not my usual language nitpicking: you explicitly mentioned a "float carb", must I understand there are non-float carburettors around?

[Jan Olieslagers]

FWIW: two or three years ago, I afforded the luxury of half an hour's mountain touring from LFNA Gap - as a paying passenger - in a Rotax912-powered FK9. I well remember the pilot-owner switched off the aux fuel pump immediately after starting the engine, with the dry comment "that one only increases fuel consumption" though the place IS high and the day WAS hot - a likely environment for vapour locking, I should think. But it was just one more beautiful flight, toally incidentless. Indeed I hope to fly it again, as a PIC now.

[SNS3Guppy]

Out of sheer curiosity, really not my usual language nitpicking: you explicitly mentioned a "float carb", must I understand there are non-float carburettors around?

Yes. Pressure carburetors are also in used. However, I think Silvaire1 was also referring to injection. In the case of injected engines, changes in boost can have an impact on engine operation.

[FlyingStone]

First of all, let me say I believe knowing your aircraft inside out can contribute to flight safety, since you cannot make general rules/procedures that will work in any aircraft.

I think we are mixing two types of fuel pumps here - auxiliary and boost pumps. Auxiliary fuel pump (at least from what I know) provides positive fuel pressure during low RPM (and thus low pressure from engine driven pump), since at very low RPM fuel pressure supplied from engine driven pump may not be enough for the engine to fire. It is also used when suspecting a vapour-lock has occured in the fuel systems. In the aircraft I've flown, using of auxiliary fuel pump doesn't change the fuel pressure significantly and isn't capable of shutting down the engine by enriching the mixture to the point where combustion isn't possible. It should also be added that most fuel systems are designed so that the auxiliary fuel pump isn't a means of providing aditional fuel pressure/flow to the engine during takeoff/landing (go-around), but as a redunancy should the main engine driven fuel pump fail.

On the other hand, boost fuel pump (sometimes called prime pump) is entirely different thing. It provides additional fuel flow when required (basically only during the prime/start phase) and on principle shouldn't be used in flight, except if you REALLY know what you're doing or the POH states you should, since boost pump is capable of "drowning" your engine with excessive fuel and thus putting out the "fire", which is most probably the last thing you want during takeoff or landing.

But as said before, following POH and knowing your aircraft's fuel system is a good way to avoid any trouble.

[Jan Olieslagers]

Thank you for pointing out the difference - I never imagined more duality than the switch being "on" or "off". Of course one should consult the plane's documentation, which is supposed to have it all - but apart from that, is there any way of telling an auxiliary pump from a boost pump? Different plumbing?

Mind you, the opening post was clearly about an auxiliary fuel pump.

[patowalker]

Jan,

I think you will find the type of aircraft you and I fly conform to

CS-VLA 991 Fuel pumps
(b) Emergency pump. There must be an emergency pump immediately available to
supply fuel to the engine if the main pump (other than a fuel injection pump approved as part of an engine) fails. The power supply for the emergency pump must be independent of the power supply for the main pump.
FYI, the FK-9 manual says the electrical pump must be ON for take-off and landing. It is a FACET automotive pump, which costs about £50.

[SNS3Guppy]

The terms "boost pump" and aux pump are used interchangeably, depending on context. Boost pumps may or may not be auxiliary pumps, and auxiliary pumps may or may not be boost pumps.

In some installations, gravity feed is insufficient to keep the engine running, and the use of boost pressure may be necessary to feed the engine, supplement fuel flow, move fuel to the pump, or supply fuel within the tank to the fuel port in that tank.

In some cases, a boost pump can serve as a necessary source of fuel pressure and is required at all times during flight. In other cases, it's used as a backup pump, and in other cases, only at certain times of flight.

Incorrect use of the boost pump can have very unwanted results.

Knowing engine response and the fuel system may prevent making a bad situation into a worse situation. A loss of fuel through a ruptured fuel line may be increased, worsening a fire potential or a fuel loss, when adherence to checklists and procedures, as well as a good understanding of the situation, may prevent such a case from getting worse.

Boost pump use may affect usable fuel; one may suffer an engine failure due to lack of fuel, yet have ample fuel on board. No way to get to it, but it's there. Auxiliary pumps are often required to move fuel to a usable location, or even to move fuel within a tank to make it available during certain flight conditions or fuel levels.

Fuel pumps return a certain amount of their fuel as "bypass fuel" to a location that varies from the same tank from which the fuel was drawn, to the inlet side of the fuel pump, to a different tank than that which is in use. By increasing boost, one may increase the bypass fuel flow. In many light piston twins, this causes a greater amount of fuel to be drawn from the tank in use, and returned to a main or auxiliary tank. One can quickly reduce the expected burn time from a given tank or tank system to a much lower number, while inadvertently transferring fuel to a location that isn't in use or can't be used. This form of mismanagement is common in light twins. Some models, such as the Cessna 337, have experienced a disproportionately high number of fuel mismanagement incidents.

Try a takeoff in a turbo 210 or 207, and apply full boost during the takeoff roll. See what happens.

[Kengineer-130]

I find it faintly ridiculous that using a fuel pump can cause engine failure?? I cannot claim knowledge of many light aircraft, but I have been an engineer in the RAF (Engines & Airframe) for 12 years, a PPL for 6 yeas, and have NEVER heard of using an aux pump as well as the EDP to cause a rich cut/ engine failure?

It would be utter madness to design a fuel system like that, and I highly doubt the CAA/FAA would allow it. There should be a pressure reducing valve/ recirculation valve to keep a constant fuel pressure, and to prevent over-pressure, be it carb or fuel injection. As I say, I cannot speak for all types, and maybe some older/homebuilts have this trait, but flying the Warrior, the checklists require the aux fuel pump on anywhere below 1000'..

[SNS3Guppy]

It would be utter madness to design a fuel system like that, and I highly doubt the CAA/FAA would allow it.

That would be a wrong opinion.

I'm looking at the aircraft flight manual supplement for the Cessna 421, relating specifically to the pump and switch installation, which states "If the auxiliary fuel pump switches are placed in the HIGH position with the engine-driven fuel pumps operating normally, total loss of engine power may occur." This is not uncommon, and can be found to be the case in a number of light aircraft.

In many installations, when excessive fuel pressure or flow is present, a fuel bypass is opened. The result of forcing it too much with excess pressure can be to allow the fuel pressure being fed to the engine to drop, and the engine to die. In other cases, the engine mixture can be forced too rich or the engine flooded, and the result will be that the engine loses power or fails.

Again, know your system. Statements that it can't happen and that such notions are insane, is utter nonsense, and shouldn't be offered to those who might not know better. KNOW YOUR AIRPLANE!

[david viewing]

Fascinating discussion chaps but I suspect the answer to the OP's question might be a bit more prosaic.

The Cessna (172R/SP) fuel pump makes an excruciating grinding whining noise that's likely to have passengers bailing out and passers by running for cover. Leaving it on routinely would create the impression of imminent death by exploding fuel pump.

The PA28 pump on the other hand just ticks away inaudibly in the background and wouldn't startle a starling who'd nested in it. And it does tick away through the full duration of many flights, until it fails through neglectful overuse.

So the Cessna pump can't be left on because of the complaints from neighbours. But the Piper one can, because no-one (including the pilot) notices.

PS I wonder what the continuous operating life of one of those Cessna pumps is..

[Big Pistons Forever]

That would be a wrong opinion.

I'm looking at the aircraft flight manual supplement for the Cessna 421, relating specifically to the pump and switch installation, which states "If the auxiliary fuel pump switches are placed in the HIGH position with the engine-driven fuel pumps operating normally, total loss of engine power may occur." This is not uncommon, and can be found to be the case in a number of light aircraft.

In many installations, when excessive fuel pressure or flow is present, a fuel bypass is opened. The result of forcing it too much with excess pressure can be to allow the fuel pressure being fed to the engine to drop, and the engine to die. In other cases, the engine mixture can be forced too rich or the engine flooded, and the result will be that the engine loses power or fails.

Again, know your system. Statements that it can't happen and that such notions are insane, is utter nonsense, and shouldn't be offered to those who might not know better. KNOW YOUR AIRPLANE!

Ab initio flying training involves teaching a student a lot of new things. The information overload at the begining can be quite severe so in order to make things simpler for the student rote learning is used. So for instance the student is told to always put the boost pump on for takeoff, probably without a lot of explanation. The problem occurs when as often happens, the context that provides true understanding is never addressed later in training. This is why you get PPL's who always fly with the mixture full rich, regardless of the altitude, always cruise at the same power setting, regardless of the distance of the flight or the winds, and always apply full carb heat at the first power reduction even if the temp is + 30 deg C. It is inefficient but for the most part not unsafe. Where it does become unsafe is when these "one size fits all" flight schoolisms are applied to aircraft other than your average Cessna/Piper trainer. Unfortunately good systems knowledge is not a requirement in order to be a flight instructor and many instructors just mindlessly pass on the flight school urban myths that they were told.

My recommendation to all PPL's is to use the web to do some research. There are lots of excellent resources available that will provide a ton of useful information. Start with the Continental and Lycoming home pages. Lycoming in particular has a great downloadable manual of tips and procedures. The columns on AVWEB are also a great resource. If you are an aircraft owner than you should belong to the type club for your aircraft. I own a Grumman AA1B and the type club (American Yankee Association, aya.org) has provide me with much type specific operating and maintainance information)

If you are a new pilot moving up to different and or more complicated aircraft than I highly recommend you start with becoming very familiar with the pilot operating handbook. When you get checked out you should challenge any deviation from the POH procedures and your instructor better be able to offer a full explanation of the what/how/when/why a deviation is warranted. The typical "well this is the way we do it here" is not good enough IMO.

[FlyingKiwi_73]

As a bulk standard piper driver i have the Aux pump on until 1000ft, thats my first mini SADIE check, Pump Off, Landing Light Off (if needed) TandP's for the climb.

500ft or below ... you'd look stupid if it quit on you. at least at 1000ft i have allot more options.

[Morrisman1]

I find it faintly ridiculous that using a fuel pump can cause engine failure?? I cannot claim knowledge of many light aircraft, but I have been an engineer in the RAF (Engines & Airframe) for 12 years, a PPL for 6 yeas, and have NEVER heard of using an aux pump as well as the EDP to cause a rich cut/ engine failure?

Someone please correct me if I'm wrong but in many injected aircraft the fuel pump is capable of supplying high pressure fuel in the event of a engine driven fuel pump failure. If this was turned on when not necessary there would be too much fuel delivered to the engine and subsequent rich mixtures to the point where engine failure was possible.

I should go back and read the flight manual again but Im sure on the PA34-200T Seneca it specified that the High setting for the fuel pump is not to be used when the engine driven pump is running correctly. It also has a low setting which is to be used when specified in the QRH but not under normal circumstances.

In the carburetor planes I've flown I have been taught to have the aux fuel pump on till 400' agl. In the PA28-181 Archer III which is fitted with a coarse pitch prop in a climb at Vy (76kias) the rpm is approximately 23-2400 and the engine driven pump cant keep up and the pressure drops close to 0.5 psi on the gauge, In that situation I will leave the aux pump on till top of climb.

[Sir Niall Dementia]

A&C

:D:D:D:D:D:D

You are right, and one day, I fear it will happen.

SND

[Contacttower]

I may actually just contact Cessna about this...best way to get a definitive answer on this.

[Kerling-Approsh KG]

Good luck... Sadly, in my experience it's not... Even on multiple-million $ aircraft...

[FlyingKiwi_73]

Hmmm I just re-read the intial post.

"In the event of failure of the engine driven fuel pump, use of the auxiliary fuel pump will provide sufficient fuel to maintain flight at maximum continuous power."

Its poorly worded as so many manuals are. If you flip it logically this is saying loss of engine pump and gravity feed will NOT be suffcient in a Max power climb (like just after rotation).

The clue is in the name :-) Auxillary = additional; supplementary; reserve. Boost pump on the other hand, no idea never flown an A/C with one.

[SNS3Guppy]

As previously stated, the terms "aux pump" and "boost pump" are used interchangably in many cases, and have no specific universal implication. A aux pump may or may not be a boost pump. A boost pump may or may not be an aux pump. In some aircraft, the boost pumps are continuous duty pumps which are required for operation; they are a necessary, integral part of operation, and are not auxiliary at all. In other cases, boost pumps serve dual purposes, have dual settings and can be used as additional pressure to reduce vapor lock or fuel fluctuations, but can cause engine failure on a high setting...but which will handle engine-driven pump fuel flow functions in the event of an engine driven pump failure.

In other cases, aux pumps are boost pumps that boost fuel pressure, but are not necessary for all phases of flight; some pumps are both, some are one or the other, some are one or the other, some are neither. Some light aircraft use injector or motive flow pumps to move fuel inside the tank, or from tank to tank, which operate any time fuel flow exists (and which have no motor).

Some discussion has been had about low wing airplanes, which do not gravity feed well in the event of an engine-driven fuel pump failure, and in which the use of an auxiliary pump is sometimes necessary to move fuel to the engine in the first place. These installations shouldn't be confused with high wing aircraft, or low wing aircraft with high fuel tanks (the Ercoupe, for example), which use pumps for various reasons.

Not mentioned thus far are also transfer pumps, which don't feed engines at all, but only scavenge fuel from one tank to move it to another.

Again, as already well established, know the airplane systems, and know the procedures and manual.

I may actually just contact Cessna about this...best way to get a definitive answer on this.

No, it's not. Ask them about warnings regarding the use of slips and full flaps, while you've got them on the phone. Chances are that whomever you talk to there won't be able to tell you.

If you call the airframe manufacturer to ask about the engine, you're talking to the wrong source; you should be talking to the engine manufacturer. Unless of course you're talking about restricted ranges for operating the engine, such as midrange radial red lines on your RPM indicator, in which case much of the time you should be talking to the propeller manufacturer. Good luck finding someone there who knows the implications of that propeller on your particular engine, or the specific reasons and the harmonics that govern them.

Calling the manufacturer isn't necessarily the panacea that you might imagine it to be, and what you get over the phone, or even in writing doesn't constitute manufacturer approval, nor an operating authorization or limitation. Your aircraft flight manual and other approved operating documentation, on the other hand, does.

[FlyingKiwi_73]

...still leaving the pump on till 1000Ft...

[SNS3Guppy]

That's fine. How do you know the pump is working?

[Big Pistons Forever]

That's fine. How do you know the pump is working?

Good question. How many pilots check the operation of the aux pump before engine start ?

[SNS3Guppy]

Or during operation. For example, how many look for a reaction when moving a control such as a switch, lever, etc? Is anyone looking for a change in the ammeter when the pump is turned on? If the pump has an "on" light, does anyone actually know whether the switch activates the light, or the pump circuitry does?

It's very important to verify systems operation; not just turn on the switch.

[FlyingKiwi_73]

Easy answer, Fuel Pressure and Ampmeter part of the checks on run up.

Turn off the pump and 1000ft, check fuel pressure remains.

[Kengineer-130]

Guppy, I was not saying it doesn't/ can't happen, I am just amazed that such designs can exist :ugh:... As I said, I fully respect that you know a lot more about various light aircraft than me, as I have only flow the 150,152 and various Warrior varients.

That is the best advice, learn the system you are operating :ok:Pilots and Engineers often have differing ideas of what they want, which can lead to all sorts of problems! Good discussion though, very interesting :ok:

[Big Pistons Forever]

Easy answer, Fuel Pressure and Ampmeter part of the checks on run up.

Turn off the pump and 1000ft, check fuel pressure remains.

Assuming we are talking about you average Pa 28 or equivalent, the only positive way to know the boost pump is working is to turn it on before start and observe the fuel pressure gauge. Runup should be done with the fuel pump off to ensure the engine driven pump is functioning. As was noted in another post, for most aircraft the ammeter is often not sensitive enough to see the load when the pump is switched on so this is often not a very useful check. As for turning off the pump at 1000 feet the rule of thumb I use is I will not turn off the pump in a situation where an engine failure would be "inconvenient" as from personal experience I can tell you that if the engine driven pump has failed during the takeoff you won't have to look at the pressure gauge to know you have a problem.......the sudden silence when you switch off the boost pump will be the big clue.:uhoh:

[SNS3Guppy]

Therefore you cannot readily determine if the electric pump is working when the engine is running (the ammeter is +/- 60 amps and lacks sufficient resolution).

You may not be able to see an increased load with the pump on, but then you won't know what value to look for without some digging in the maintenance publications.

Instead, look for a bump in the ammeter indication when turning the switch on, or off. Generally with most electrical components, you'll see a slight change in the ammeter when applying or removing a load, even if it's hardly perceptible. Always look for a reaction when you move a switch, lever, or control.

You also have the option of shutting off the generator field, and checking for a battery discharge. Generally you'll see a better indication of a load when applied directly to the battery without intervention from alternator/generator; it's one option for checking for an electrical reaction when you move the switch.

The other choice, of course, is to listen for the pump prior to engine start. This doesn't address your pump's operation in flight.

A good habit to pick up is checking the circuit breaker for your pump or equipment any time you turn something on or off. If you have inoperative equipment, that should also be one of the first places you check; verify the switch is where you want it, then check the circuit breaker.

I flew a single engine airplane several years ago that had a new hydraulic system installed. The previous year, the hydraulic pump sheared it's drive shaft, and I made an emergency landing as a result. The following year when I returned to fly the airplane, the engine-driven hydraulic pump had been replaced by an electrical dual-pump installation that cycled off a pressure switch. If the pressure dropped too far, the pump would start up, restore the power, then shut off.

I was returning from a fire drop when I smelled smoke. As I did an overhead break approach to a landing, the cockpit filled with smoke, and by the time I touched down on the runway, I was quite aware of being on fire. The pressure switch for the pump had been set improperly, and following the use of the hydraulic systems during the flight, the pump ran continously. I didn't check the ammeter (I didn't think about it; I had flown the same type airplane for seven years with engine-driven hydraulic pumps, and being a creature of habit, I failed to verify the pumps had shut off. They weren't continuous-duty motors or pumps.

The pumps got hot, burned a seal, leaked, and then the assembly caught fire, burning down near the right wing root. By the time I reached mid-field during the landing roll, I couldn't see much out out of the cockpit, and it was painful to see or breathe.

I violated a basic rule of operation; always verify proper operation, In this particular case, the pump switches were supposed to be turned on and left on, with the pumps automatically cycling off the pressure switch, so I had no reason to keep checking the ammeter as I turned pumps on or off...because the switches were to be left alone until shutting down after the flight. What I should have done is paid closer attention to the ammeters in flight. Live and learn; I pass that lesson on to you, hopefully so you can learn it without having to live it.

[FlyingKiwi_73]

just to be clear, its obvious in a PA28 that the Aux pump is on, even when the engine is on, you can hear it. I check the fuel pressure at several stages.
I switch off at 1000ft as its a safe height to find out the primary has failed, i normally climb in the circuit due to hills and proximity of airspace,(letting people know i'm vacating west/east) i usually reach 1000ft failry close to field so if i lost the engine i could (and have in the past) been able to glide back to the runway... i practice glide and flapless approaches every now and then.

[SNS3Guppy]

just to be clear, its obvious in a PA28 that the Aux pump is on, even when the engine is on, you can hear it. I check the fuel pressure at several stages.

Not on a busy ramp. Not when the engine is running. That means there are plenty of occasions when one may not be able to hear the engine running.

Sometimes one can feel the vibration. Depending on the pump, one may not be able to hear it.

[FlyingKiwi_73]

On our ramp, all you can hear are echo's :-) although there was a piper sports cruiser there this weekend... the club are test driving it... looks nice.