PA28 - electric fuel pumps.

[Bear Cub]

I posted this thread on Sunday night - on Monday morning my e-mail told me six people had replied. When I attempted to log on, I met the "Server Down" situation.

Now it seems that on reparing the server - the thread has been sent to cyberspace somewhere. Would the six of you mind re-replying?

Basically what I asked was - although I know it has been asked before - at what height/altitude do YOU teach to switch off the elctric fuel pump in a PA28...and WHY?

One school I fly at teaches 500' on QNH from an airfield at 85' amsl - reason "'cos that's what we do on the twin" (go figure).

Another school I fly at says top of climb - because that's when you are changing to the tank full of Mogas.

Another, 1000' QNH from an airfield at 25' amsl - because that is when you are leaving the circuit.

The flight manual for a brand new Warrior III that I use sometimes says "at top of climb" - and the manual for a 151 says "once a suitable altitude has been attained".

What's YOUR height/altitude, do you vary this for airfield elevation...and WHY?

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Hunting is bad!!
Support the right to arm Bears!!

[A and C]

The bottom line is how quick can you switch the electric pump back on when the engine stops if the engine driven pump fails.
I think that 1000ft AGL would give a well trainned student enough time to do the corect drills and get the engine back.

Eny outfit that states that "we do something at 500ft because we do it that way on another aircraft" wants to be avoided, aircraft operating procidures should be the best for THAT aircraft not another in the fleet.

[Localiser]

I always switch the fuel pump off at 1000' QFE in every S/E Aeroplane that I fly.

Also, one little tip a instructor on my PPL gave me, I still do! It is to keep your finger on the electric fuel pump for a couple of seconds after you have switched it off. Then, if the mechanial fuel pump has failed and the engine starting 'playing up', you could flick the electric fuel pump back on and RTB... Crisis over!

Don't flame me! Just a suggestion ;)

[Wee Weasley Welshman]

Personally I always forget the little bugger. I teach off at 1000ft though...

WWW

[dragchute]

300 feet above aerodrome elevation BUT guard the switch for a few seconds to ensure that fuel pressure is stabilized within the green arc.

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dragchute
email: [email protected]

[Bear Cub]

Not growling at you, promise - but have any of the "guard the switch for a few seconds" people ever turned off the fuel selector (at 2,300 RPM, os so) to see how long it will take for the active fuel line to drain out?

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Hunting is bad!!
Support the right to arm Bears!!

[Oleo]

Yeah, turn the switch off at a "safe" height and monitor the fuel pressure.

When learning I was taught to turn it off at 300' and when doing circuits I would be switching it on and off every circuit. I taught my own students to leave the thing on in the pattern: less risk of it failing from constantly being abused.


Similarly, a tip I picked from another instructor is to keep your hand on the gear lever until you get the three greens.

[chicken6]

500' AGL, enough time to realise, swear, and try one restart before picking a paddock and landing. Mind you, when I learnt on PA28-161s there were always paddocks available in the middle of 50 nm each way of flat farmland.

If I was to teach on a PA28 (or is it P28A?)now, I would teach "when you can land without your engine any more" i.e. about 500'-700'AGL.

Personally though, I frequently forget, flying Cessnas too much without reminding myself that I should at least look for a pump switch. One of the hazards of mixed fleets.

Safe flying

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Confident, cocky, lazy, dead.

[foxmoth]

1000 ft (agl) is what I have been taught at a number of locations and is what I teach myself. Below this seems unnecessary and far to likely to lead to a brown seat for my liking.

[OneMileHigh]

1000 ft I was taught, and that's what I do.

At the end of the day 1000 ft between, oh **** it's gone quiet and huge sigh of relief seems to me to be only sensible.

As to why.....The lecky pump can mask a faulty mech pump, so above 1000 ft when the mech one fails you know about it, then you can retrieve the situation with the lecky one and plan accordingly.

I include the fuel pump as part of my FREDA's so my chances of forgetting are reduced.... :)

[Flange]

I was recently told by a colleague of a student who turned off the pump at 700'AGL (1000'QNH)on a PA28 during climb out. The mechanical had failed, the engine stopped but windmilled, he turned the electric back on again and got power back at 100'AGL.

[Lawyerboy]

Mr Guru Man, Trevor Thoms he say "when at a safe height to do so, or at about 500ft agl", doesn't he? My instructor insists I leave it on in the circuit, though.

I fly a PA38 by the way, if that makes any difference.

[This message has been edited by Lawyerboy (edited 19 July 2000).]

[dragchute]

Lawyerboy,

I would ask your instructor these questions.

If I fly a circuit period with the electric fuel pump 'ON' continuously, how do I know the mechanical pump hasn't failed? and,

If the electric pump subsequently fails and I now have neither pump, are my forced landings up to speed?

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dragchute
email: [email protected]

[DB6]

Dragchute, you find out if the mechanical pump's failed when you switch off the electrical one after landing. I don't think I'd switch it off in the circuit just to find out if the other one's still working. B-b-bollocks to that. We switch them off at top of climb and back on at rejoin (also pre-stalling etc).
Cheers DB6

[This message has been edited by DB6 (edited 19 July 2000).]

[dragchute]

DB6,

Let me spell it out a little more clearly for you! Lawyerboy (above) suggests he operates the entire circuit detail with the standby pump ‘ON' . Supposing on the second circuit the mechanical pump fails. This important fact is masked by the continued operation of the engine, fed by the electric fuel pump. If he opted to turn the electric pump ‘OFF' at a safe height after take-off as most of us do, he would recognize the failure and be in a position to reinstate the pump and ‘full stop' off the next approach.

However, should the electric pump also fail some time later in the detail, he is left with just the ‘forced landing' option. I would prefer to know after each take-off if the fuel system is fully operational and not just being propped up by an emergency system. To leave the pump ‘ON' at all times in the circuit partially defeats the purpose of system redundancy.

Finally, many instructors build in such simplified techniques for students rather than spending the time in adequate explanation and the development of safe operating procedures. Such techniques developed at an early stage require considerable effort to modify when your student reaches my check and training department!

Regards

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dragchute
email: [email protected]

[Lawyerboy]

Dragchute

The suggestion then, I assume, is that the electric pump should be turned off at whatever we consider a safe height to be and not actually switched back on again until on finals? Or should that be on base leg, downwind, whenever we reduce power...?

[dragchute]

Lawyerboy,

I always include fuel pumps in the down-wind checklist. In the standard BUMFH checklist that calls up (F)uel, check pump/s 'ON' and select fullest tank/s. Leave the pump/s 'ON' until clear of the runway for a full stop or at a 'safe height' with a touch-and-go.

A 'safe height' is something that most manuals don't specify. In my experience pressurisation of the system after running a tank dry (or failure of the engine driven pump) may take ten to twenty seconds depending upon the backup system. The Tomahawk Information Manual may be more specific under section 4 or 7.


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dragchute
email: [email protected]

['I' in the sky]

Climbing - off at 1000' agl
Desceding - on once commited to going below 1000' agl.

Most typical circuit heights 800' or 1000' agl so stays on all round the circuit.

Easy !

[DB6]

Nah, I knew what you meant, Dragchute, but I am happy to accept the risk of both pumps failing on the same flight. It's enough for me to check after each flight when I'm safely on the ground.

[Lawyerboy]

Dragchute - finally got up in the air again yesterday so had a chance to think about it a little more clearly. With the PA38 the electric fuel pump gets switched on just before you crank the engine and then switched off again for taxi. Pre takeoff checks at the hold then include 'Fuel pump - on'.

Why, then, if you're staying in the circuit, test the mechanical pump again at, say, 500ft agl if you've already tested it during taxi? If it were going to fail it would have done so before takeoff.

[dragchute]

Lawyerboy,

There is some argument to suggest that component failures occur during periods of high mechanical workload. On take-off for example when an engine is operating at maximum RPM rather than in cruise or descent. My own experiences have been about fifty/fifty though.

A system that ‘checks-out' on the ground may fail during the take-off. If this is masked by a standby system for subsequent take-offs, because the standby system has been left on, the safety feature of dual systems is removed.

The purpose of dual pumps may also be the supply of pressure to the system to prevent vaporization. Failure of one pump may result in fuel starvation under certain critical conditions. I have experienced some problems in that area with fuel injected engines operating in outback Australia during summer.

I don't consider a standby fuel pump to be manufactured to the same standard as a constant duty pump. Over-use of the standby system may mean that it does not ultimately survive the full engine overhaul period.

Another point is the checklist. Why use one checklist for cross-country flying and a different checklist for circuits? (Climb...pump/off, check pressure... Downwind ...pump/on, fullest tank....)

My advice - turn it off at a safe height after take-off and back on during down-wind checks. Minimizes pump usage, extends pump life, confirms operation of the primary system and instils sound airmanship with just one set of standard operating procedures.

Hope this helps.

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dragchute
email: [email protected]

[A and C]

Dragchute i think your ideas and thinking on the subject are 100% correct but i would just like to add that in 20 years as a licenced engineer (A&P to the americans) i,v only seen one mechanical pump fail on carburetord engines.
I dont think you should talk about injected engines in this thread as this may cloud the issue as what is safe for one type of injected engine is the quickest way to have a failure no another.