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Fuel Pump on TO and APP

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Fuel Pump on TO and APP

Old 3rd Feb 2019, 07:09
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Fuel Pump on TO and APP

Will start with a little example:
Yesterday, first flight for a season for a airport 100miles away. I was invited to fly a bit on Tecnam P92. When I got there, they were already in the air. I hopped in for couple of circuits. That turned out to be unexpectedly long 1+ hour flight.
Now the Tecnam owner decided to not turn off the pump for the circuits. Then, at some point some trike guys appeared and started prepping for their season opening obviously. We - actually not me, as was in for the ride but my friend said: "Better stay away from them". So "we" decided to go for 5 minutes in the practice are to see how it will unfold with the traffic so to decide what to do next. Since it was calm and smooth, my friend said: let's go on a short trip. And we did. 28 miles or so. We went there, made a huge orbit over the airport at cruise altitude and headed back home where....we saw the fuel pump still ON and that was shortly before entering the pattern.
Ooops!
At that point we have spent quite some time in the air already.

Now, there has been a discussion shortly after, is the pattern work /as well as maneuver practice/ requires Pump ON. Not solely on Tecnam, but others too. Since I have most of my experience on Cessnas I decide to dig deep into it and try to learn more.
There are a lot of threads and as many opinions as participants.
How about your experience?
Leaving it on won't hurt, but will lead to a short pump life. On the other hand, turning it on and off on the circuit is not a good idea either, besides maybe practicing your work in the cockpit.
Any thoughts and probably sharing some events?
I see no particular problem with leaving the pump OFF especially with high wing as P92. Even with low wings. Yes, in case of main pump failure with some aircraft that can lead to engine stop in flight, but then the procedure walks you through the pump anyhow.
Some random guy overheard us talking at the airport and passing us by asked: do you know the price of a new pump? Better turn it off as soon as practical.
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Old 3rd Feb 2019, 09:06
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In the PA28, we leave the electric, secondary, pump on for circuits and any flying below 1,000' AGL, but turn it off for the cruise. More importantly, in my view, is that having it off at a safe height means that any impending failure of the mechanical engine-driven pump can become apparent, in plenty of time to do something about it. If you have the electric pump on all the time, how do you know what the engine pump is doing? This is also why we start the engine and do all the ground checks with the electric pump off, then turn it on during the Vital Actions before departure.

TOO
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Old 3rd Feb 2019, 10:11
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@ Sporty123.
Don't go beating yourself up over this . It's not as if you've gone off with your tow-bar attached , or done a 'gear-up' landing is it . I'm sure that many have done a similar thing when flying a/c with elec. booster pumps . The only mistake you've made is putting it onto a forum and inviting the worlds committee of experts to pick the bones out of it .

In reality , all you've done is a flight , barely over an hour . Considering you had originally planned to stay pretty close-in anyway , then the boost pump probably hasn't really been left on for much longer than if you'd been circuit-bashing and in the big picture of things , I hardly think that you've hastened the pump into a premature death .
When the fuel px is being provided by the engine-driven pump , the elec. pump [if on ] is really only 'loafing' and the fuel does also provide a cooling & lubricating effect .

Put it this way ...You probably won't do it again in a hurry will you . So you've emerged from it as a better pilot..

As for the 'airfield expert',,,[ "do you know wot a new pump costs"],,,,,,Golly , it must be difficult having a completely unblemished flying career...!..
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Old 3rd Feb 2019, 10:24
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The one thing that will cause damage to a pump is running dry. Seeing that you obviously didn't do this, I wouldn't worry about it. I'm sure no harm was done - but lesson learned.

I replaced the mechanical pump on my older car (carburettor equipped) with an electric pump - just like many British cars used to have. It has been probably one of the most reliable items on the car. I stripped it after fifteen years and it was still in pristine condition inside. Also, bear in mind that the electric fuel pump on any modern fuel injected car runs all the time.
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Old 3rd Feb 2019, 11:13
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I agree with earlier: as long as the pump does not run dry, it won't get any harm. Still, there's not much use in activating it, actually I am not sure this particular type of plane requires one. It depends much on the type and configuration of the plane, and on the engine and its mechanical fuel pump.

The P92 is a high-winger, right? With the fuel stored in wing tanks? And the engine is a Rotax 912, probably the 100HP version 912S?
Well, my own pride and beauty is of exactly the same configuration, except it has a 912 not a 912S, and there is no electrical pump at all. And (touching wood!) I have yet to come into fuel feed problems. Gravity is a quite reliable force, as every pilot should know.
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Old 3rd Feb 2019, 11:17
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This is also why we start the engine and do all the ground checks with the electric pump off, then turn it on during the Vital Actions before departure.
This is type dependant. In a Robin DR400 the first item in the FM under Engine Starting is 'Electric pump on'. Experience shows that unless it is done the engine usually fails to start - especially the first start of the day. Personally I then turn it off until I do pre-take-off checks so I know that the mechanical pump is working - not to avoid wear on the electric pump. In flight I leave it on except for the cruise - but since most of my flights are towing gliders that means it's on for most of the time.
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Old 3rd Feb 2019, 12:41
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Originally Posted by TheOddOne View Post
If you have the electric pump on all the time, how do you know what the engine pump is doing?TOO
By keeping half an eye on the fuel pressure gauge? Nah, make that 1/100th or even 1/1000th of an eye. Your state-of-the-art EFIS may probably even sound an alarm on occasion.
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Old 3rd Feb 2019, 19:11
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I was more of a passenger than an active pilot in this case, because my experience with 92 dates back from 16 years ago and it is very limited. So I am not beating myself over it anyhow. I didn't bother to read the POH the night before too.
The thing is that on the downwind we saw the guys gathering up and we decided to turn and hit the practice area. However, we forgot the pump at that point and since there is no such point in the cruise checklist that pump went into oblivion.
Interestingly, I saw that some Tecnam flyers turn it on and off constantly even in the pattern. Maybe that is not such a bad idea after all. Better mess up the button than the pump itself.
On the other hand, it beats me why so much attention to that specific item, since if /IF/ no unusual circumstances - the pump won't be needed neither for landing nor take off. The plane flies pretty normal without it.
Maybe it is a rotax thing, those pumps?
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Old 3rd Feb 2019, 19:30
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Maybe it is a rotax thing, those pumps?
At the contrary, as I already pointed out. There's plenty of Rotaxen flying around without auxiliary electric fuel pump - all high-winged, of course, with the fuel stored in the wings. It is the Cessna's and similar antiques that insist on having one, for their own reasons, no doubt. One reason may be that AvGas is more subject to vapour locking than the MoGas that Rotax mostly burns. Though I had no issue on the rare occasions I ran mine on AvGas.
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Old 3rd Feb 2019, 20:30
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In theory the 'extra' fuel pump is not needed for normal flight.
A fuel pressure gauge will tell you if the pressure is sufficient - but if the mechanical pump fails spotting the needle sitting on zero may take some time - as engines tend not to run without fuel a auxiliary / extra / electric or whatever pump makes some sense.
I had an Emeraude some time ago and I had a mechanical pump failure (due to mechanical wear on the camshaft / pump), no fuel pressure indication fitted, but when the nose went up, the engine faltered, when the nose went down the engine recovered - quite exciting as I climbed to circuit height in a series of steps using the fuel in the carburettor bowl!

So if I had an auxiliary pump there would been no drama - which gives a pretty good idea of when an auxiliary pump should be switched on.

I would also comment that Avgas is MUCH LESS likely to suffer vapour look than Mogas - hence the temperature limitations for Mogas approval!


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Old 3rd Feb 2019, 23:33
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There's plenty of Rotaxen flying around without auxiliary electric fuel pump - all high-winged, of course, with the fuel stored in the wings. It is the Cessna's and similar antiques that insist on having one, for their own reasons, no doubt. One reason may be that AvGas is more subject to vapour locking than the MoGas that Rotax mostly burns. Though I had no issue on the rare occasions I ran mine on AvGas.
Firstly, if the aircraft requires a fuel pump it must also have a back up pump. It is not that Cessna "insist on having one for their own reasons". Secondly, avgas is not more subject to vapour lock than mogas. Quite the opposite. Mogas varies by region and season, but in general it is more prone to vapour lock because it is not formulated to be used at high altitude.
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Old 4th Feb 2019, 02:54
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If the engine or fuel system requires a fuel pump, the aircraft will have two per engine:

Sec. 23.991

Fuel pumps.

(a) Main pumps. If there are fuel pumps to maintain a supply of fuel to the engine, at least one pump for each engine must be directly driven by the engine. The fuel pumps must be adequate to meet the flow requirements of applicable Sec. 23.955.
(b) Emergency pumps. There must be emergency pumps to feed the engines after the failure of any engine-driven fuel pump other than a fuel injection pump (a pump that supplies proper flow and pressure for fuel injection when the injection is not accomplished in a carburetor) approved as part of an engine.
(c) Warning means . If both the normal pump and emergency pump operate continuously, there must be a means to indicate to the appropriate flight crew members a malfunction of either pump.
It is common, and wise to have the electric fuel pump on during takeoff, simply to remove criticality should the engine driven pump fail during takeoff. That said, it is required that the engine be capable of normal operation with the electric fuel pump off, as long as the engine driven fuel pump is functioning properly. Some aircraft (as two of mine) are near impossible to start on the engine driven fuel pump alone, as the electric pump is needed to pump the fuel up to the engine driven fuel pump, and it is needed for priming the engine, which is electric.

Of course, follow the instructions of the flight manual for the aircraft, and having the electric fuel pump running during takeoff is wise. But if the engine is running, it should keep running, as long as the engine driven fuel pump does not fail.

Yes, MOGAS changes volatility seasonally, AVGAS is always the same volatility. Aircraft fule pumps tend to draw fuel from a tank, rather than push fuel from a tank. The reduction in fuel pressure while drawing fuel, particularly at altitude tends to promote boiling of highly volatile fuel, which is why MOGAS being pumped into the engine, from the engine side of the fuel system is more vulnerable to vapour lock (bubbles, rather than liquid).

Forgetting something while flying, then kicking yourself for it, is a great way to learn not to forget things!
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Old 4th Feb 2019, 06:19
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What interests me more are the eventualities associated with forgotten fuel pump. In ON position mostly, but I bet that some experienced the other way around as well.
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Old 4th Feb 2019, 07:53
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The use of an auxiliary electric fuel pump varies by type. My experience is mainly with low wing Pipers so my comments will have most bearing on Piper aircraft.

On carburettor equipped models I turn the auxiliary pump on prior to start and watch the fuel pressure guage to see the pressure has risen, (This way I know the pump is working). Then it is switched off for the start. In the event of an engine fire at start up you don't need fuel being pumped to the fire. The pump is turned on during the pre take of drills (DVA's) and switched off at a safe altitude after take off and switched back on during the pre landing checks.

On fuel injected models I turn the auxiliary pump on to prime the engine prior to a cold start, switching it off once the engine is primed. The pump is then used in the same way as for a carburettor model.

I know of at least one model of aircraft where leaving an auxiliary pump on unnecessarily prior to take off, (i.e. all the time from start till take off) can actually induce an engine failure when the auxiliary pump is switched off after take off. These aircraft have the auxiliary pump fitted in parallel with the engine driven pump, at low power settings the auxiliary pump provides all the fuel and the fuel in the engine driven pump stagnates and then vapourises. Once the fuel vaporises the pump stops pumping with obvious ramifications when the auxiliary pump is switched off.
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Old 4th Feb 2019, 10:10
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There are various arguments ongoing at flying clubs and schools about fuel pumps, but the bottom line is of course: follow the POH instructions. The first post mentioned Tecnams and Cessnas, and then there's Pipers and other types, but remember that each type may have different reasons for employing electric fuel pumps, and therefore different procedures in the POH for their use. It's impossible to come to one theory about this (apart from the regulatory background as Pilot DAR explained). I was recently flying in a C172R (the fuel injected version) with three other instructors (I know, most dangerous combination possible) and I turned out to be the only one who switched the fuel pump on for take off and landing. The reasoning employed by the others went along the lines of 'mechanical fuel pumps hardly ever fail', 'it's a Cessna, you've got gravity feed' and so on, but they all ignored the fact that for a fuel injected engine, you need a higher fuel pressure than can be provided by the gravity feed in all possible attitudes. And of course they also ignored the fact that the POH clearly states 'Fuel pump ON' for take off and landing in the Normal Procedures section. Bottom line: don't get too bogged down in all these discussions and stick to the manufacturer's POH. It's still a good idea to learn as much as you can about these things, and as already mentioned, you got a useful lesson out of the original incident. Perhaps it might be useful to add a line about the fuel pump to your Cruise checks.

In addition (and in reply to the post above me), there are also significant differences between various Piper models. On a PA28RT-201T, switching the fuel pump to HI may flood your engine and cause it to shut down....
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Old 4th Feb 2019, 10:21
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Maybe Rotax equipped low winged planes are more appropriate to be discussed here. Tecnam 2002JF, Bristell, Sport Cruiser, TL Ultralight and other. Although TL don't have such procedure if my memory serves me right.
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Old 4th Feb 2019, 10:22
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Anybody here with experience on the P92 tank system? The booster pump feeds a feedback loop into the tank and how exactly depends on type. Usually the fuel loop only feeds back into one tank, so leaving it on all the time does have the danger to get out of balance in the end and also has the danger to overfill that tank.
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Old 4th Feb 2019, 10:34
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Originally Posted by Jhieminga View Post
the bottom line is of course: follow the POH instructions. ....
What else is there to be said !

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Old 4th Feb 2019, 11:57
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Exactly. The POH content isn't debatable...

Twice in PA38s I had fuel pump problems that made an RTB necessary, leaving the aux pump on gave me enough fuel pressure to keep the donkey running and got me home safe on both occasions. The reason I suspect it is switched on for TO/Landing and changing tanks is to provide extra redundancy. But if the POH says do it, I do it, whatever the reasons...
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Old 4th Feb 2019, 18:42
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With my PA28 the POH seems to be saying keep it on when below 1,000 AGL - that's what I do - occasionally I will forget to turn it off until well into my climb to cruise altitude.

Having it on below 1,000 is what seems to be important - if I kept forgetting I would keep it on all the while.

When flying circuits I keep it on all the time notionally I will be at or below 1,000ft AGL at maximum, but I do climb to maybe 2,500 on an extended downwind (sometimes 7 miles!) when making way for a 747 or airbus landing - when doing that always leave on as it seems likely to be a greater chance to forget.
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