Pa28 - preflight actions - change to fuller tank
If you ever run a tank dry in flight and fill it up afterwards, your problems are not over yet, as there may be air in the lines between the fuel selector and the tank outlet. This is the reason besides water in the fuel, to start and taxi on one tank and do the runup on the other tank (if you have two).
A friend of mine flew about one hour to a field because the local pump was U/S, ran one tank dry in the air at safe altitude, then filled up and never used this tank again until the third flight after the 'event' .He then switched to the 'fullest tank' ON THE RUNWAY just before takeoff just like it said in the checklist on the panel. There was still air in the fuel line between the tank and the fuel selector, the engine ran just long enough to stop at about 100 ft, but not long enough to put him in the houses at the end of the runway. Six months in hospital and several years before he could walk unaided again. Total loss on the aircraft.
I know from flying this aircraft earlier that it takes about 30 seconds easlly before the engine will restart after running a tank dry in the air.
A friend of mine flew about one hour to a field because the local pump was U/S, ran one tank dry in the air at safe altitude, then filled up and never used this tank again until the third flight after the 'event' .He then switched to the 'fullest tank' ON THE RUNWAY just before takeoff just like it said in the checklist on the panel. There was still air in the fuel line between the tank and the fuel selector, the engine ran just long enough to stop at about 100 ft, but not long enough to put him in the houses at the end of the runway. Six months in hospital and several years before he could walk unaided again. Total loss on the aircraft.
I know from flying this aircraft earlier that it takes about 30 seconds easlly before the engine will restart after running a tank dry in the air.
which is a fuel injected engine. Fuel injected engines simply can never be allowed to run dry as they may prove to be impossible to restart.
A simple carburated engine will not have the same problem and for aircraft which do not have a "both" position for the fuel selector running one tank dry should be considered if you are getting tight on fuel. It is better to have 3 gallons (ie half an hour) in one tank then 1.5 gallons in two tanks. Considering very low levels are not going to show on the fuel gauge running one tank to 1/4 and then running the other dry will leave you with a known and useful level with to land on. Obviously this should be very much the exception (I have only had to do this once so far) but it is something you should keep in your back pocket.
The procedure is when the engine dies, retard the throttle to idle, mixture full rich, switch tanks and boost pump on if fitted. The engine will pick up immediately and then you can smoothly increase to cruise power and re lean.
It's good airmanship to test both tanks feed ok before flight.
If you switch tanks on the ground before take off you must do a power check afterwards! If anyone doubts this try turning the fuel off at 1,200 rpm on the ground and time how long the engine will running before quitting then do the same but immediately after you've turned the fuel off do a power check. In the latter case the engine will quit within a fews seconds of turning the fuel off compared to at least a minute or so when the engine is at 1,200 rpm.
Some checklists that are around are full of holes because they are someone's opinion on how the aircraft should be operated - if in doubt consult the Flight Manual/POH.
The problem with fuel tank selection arises (usually) when the a/c is on level ground when you decide to select the "least tank" prior to start. You then taxi out and park the a/c on level ground for the runup and then many checklists say select "fullest tank" - you then look at the fuel guages and you are already (apparently) on the fullest tank! It would be better if the checklist just said "select opposite tank". Then it would be better in the pre take off check if the checklist said "Fuel - NOT off" etc
If you switch tanks on the ground before take off you must do a power check afterwards! If anyone doubts this try turning the fuel off at 1,200 rpm on the ground and time how long the engine will running before quitting then do the same but immediately after you've turned the fuel off do a power check. In the latter case the engine will quit within a fews seconds of turning the fuel off compared to at least a minute or so when the engine is at 1,200 rpm.
Some checklists that are around are full of holes because they are someone's opinion on how the aircraft should be operated - if in doubt consult the Flight Manual/POH.
The problem with fuel tank selection arises (usually) when the a/c is on level ground when you decide to select the "least tank" prior to start. You then taxi out and park the a/c on level ground for the runup and then many checklists say select "fullest tank" - you then look at the fuel guages and you are already (apparently) on the fullest tank! It would be better if the checklist just said "select opposite tank". Then it would be better in the pre take off check if the checklist said "Fuel - NOT off" etc
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
Fuel injected engines simply can never be allowed to run dry as they may prove to be impossible to restart.
Why would that be?
If an engine can be started on the ground then it can surely be started in the air.
If one slowed down enough to stop it windmilling then yes it could be a sod to restart... the starter motor would be needed, obviously.
Has anybody else noticed the "quote" button missing?
Sorry for the thread drift but (being in Greece on 3G) I have just opened up a VPN to my office and using that, the problem disappears! Looks like the Greek 3G network (COSMOTE) is eating some bits of pprune's HTML
Why would that be?
If an engine can be started on the ground then it can surely be started in the air.
If one slowed down enough to stop it windmilling then yes it could be a sod to restart... the starter motor would be needed, obviously.
Has anybody else noticed the "quote" button missing?
Sorry for the thread drift but (being in Greece on 3G) I have just opened up a VPN to my office and using that, the problem disappears! Looks like the Greek 3G network (COSMOTE) is eating some bits of pprune's HTML
Join Date: Aug 2011
Location: Netherlands
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
After checking both engines, during start-up, taxi and run-up, why doesn't a PA28 have an option of using both fuel tanks at once..? so they will run out equally? does anyone know? is it cheaper or easier to manufacture?
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
I did ask an engineer about that had he seemed to think it was something to do with the low wing tanks and the pressure head on the fuel line.
Cessna high wing types types the pressure head is enough that nothing funny starts happening when you have them combined into a single feed.
Cessna high wing types types the pressure head is enough that nothing funny starts happening when you have them combined into a single feed.
I can report from experience that the carb on an O-540, as used in the PA28-235, holds enough gas for a three minute ground run, a normal runup, and the beginning of a backtrack, having been cleared for take-off. Halfway through the backtrack the engine died. The fuel selector was off.
When we do C of A air tests it is a requirement to time how long it takes for the engine to stop using 1200 rpm with the fuel selected Off.
From memory if it is more than 2 minutes then it is a reportable defect.
Join Date: Aug 2009
Location: N/A
Posts: 167
Likes: 0
Received 0 Likes
on
0 Posts
Then there is something wrong with your aircraft.
When we do C of A air tests it is a requirement to time how long it takes for the engine to stop using 1200 rpm with the fuel selected Off.
From memory if it is more than 2 minutes then it is a reportable defect.
When we do C of A air tests it is a requirement to time how long it takes for the engine to stop using 1200 rpm with the fuel selected Off.
From memory if it is more than 2 minutes then it is a reportable defect.
The PA28 with an entirely pumped fuel system (no gravity feed unlike, say, a C172) can't be allowed to draw fuel from both tanks at once because if you get to the point that one is empty and the other part full, the pump will try and draw the least viscous fluid available - air. So, you'll get a fuel starvation engine failure whilst there's still fuel remaining.
So, only gravity fed systems are allowed to draw from multiple tanks at once.
UV - I'm fascinated by your statement that you are looking for maximum 2 minutes from a fuel system after shutting the fuel off. I can imagine a type specific minimum for something aerobatic that deliberately uses a large fuel line capacity to ensure a continuous fuel supply whilst in negative g - the Bulldog is like that for example. However, I'm not aware of any airworthiness standard that mandates such a thing, notwithstanding that what you describe seems quite sensible.
G
So, only gravity fed systems are allowed to draw from multiple tanks at once.
UV - I'm fascinated by your statement that you are looking for maximum 2 minutes from a fuel system after shutting the fuel off. I can imagine a type specific minimum for something aerobatic that deliberately uses a large fuel line capacity to ensure a continuous fuel supply whilst in negative g - the Bulldog is like that for example. However, I'm not aware of any airworthiness standard that mandates such a thing, notwithstanding that what you describe seems quite sensible.
G
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
This is theory!!!
Its type dependent Genhis and its written into some aircrafts maintence scheduals.
Basically its to test that the selector valve is working so it does actually shut the fuel off from going through the fire wall. I think its for only some valve types depending if the off position can fail and still allow fuel through.
I think some of them the selector operates a left and right flow or both and when you turn it off its a seperate off valve that closes or you have a three port left, right and blank shut off.
BUt it could be of course to do with your good point that a none gravity feed engine will stop sucking so it won't keep fuel going through the fire wall if you kill the engine.
Its only a theory its been years since I did one for a SEP and i can remeber checking the valve but can't remember if we timed it.
Its type dependent Genhis and its written into some aircrafts maintence scheduals.
Basically its to test that the selector valve is working so it does actually shut the fuel off from going through the fire wall. I think its for only some valve types depending if the off position can fail and still allow fuel through.
I think some of them the selector operates a left and right flow or both and when you turn it off its a seperate off valve that closes or you have a three port left, right and blank shut off.
BUt it could be of course to do with your good point that a none gravity feed engine will stop sucking so it won't keep fuel going through the fire wall if you kill the engine.
Its only a theory its been years since I did one for a SEP and i can remeber checking the valve but can't remember if we timed it.
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
There isn't two sets of feeds through the fire wall only one.
And the only time I have seen anything useful done with tank selections was in the US where its quite common to have one tank full of mogas for cruising around on and one full of avgas for departure and landing.
And the only time I have seen anything useful done with tank selections was in the US where its quite common to have one tank full of mogas for cruising around on and one full of avgas for departure and landing.
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
No; you use the fuel selector to draw fuel from one tank preferentially to balance the aircraft if flying with an odd number of people.
A plane will deliver better MPG, and will be easier to fly in terms of having neutral aileron forces, if everything is balanced, ailerons balanced, ball in the middle, and that usually requires the LH tank to have less fuel. Obviously you need accurate fuel gauges to do that
A plane will deliver better MPG, and will be easier to fly in terms of having neutral aileron forces, if everything is balanced, ailerons balanced, ball in the middle, and that usually requires the LH tank to have less fuel. Obviously you need accurate fuel gauges to do that
G
Join Date: Mar 2010
Location: Up North
Age: 57
Posts: 557
Likes: 0
Received 0 Likes
on
0 Posts
A Commander 114 I fly has a "both" option on it's fuel selector, as well as left, right and off. It's a low-wing. Don't have the POH to hand so can't look at the specific design of it's fuel system or any instructions regarding when to use which selector position.
Moderator
why doesn't a PA28 have an option of using both fuel tanks at once..? so they will run out equally?
Airspaces of tanks with interconnected outlets must be interconnected;
and;
There may be no undrainable points in any vent line where moisture can accumulate with the airplane in either the ground or level flight attitudes
In combination, these requirmeents mean that if you want to have a "Both" fuel selector option, the airspaces of the fuel tanks, (outboard ends of tanks on the PA28) must be interconnected, and the interconnecting vent line must not have an undrainable spot. This would mean that the vent line would have to come up out of the wing, and continue above the wing, right through the middle of the cabin, because of the dihedral of th wing making the outboard ends of the tanks higher than the inboard ends. .
This design requirement is the reason that you nearly never see aircraft with low wing fuel tanks with a "both" fuel selection available.
High wing aircraft usually have the fuel vent line cross up against the inside of the cabin roof, so as to meet this requirement, and allow a "both" selection. Though there are some high wing aircraft which do not have "both" (some Cessna 206 and 210).
re; the no both selection for low wing aircraft, avoiding giving giving the fuel pump the choice of fuel or air is most easily done by positively separating the tanks. As an aside my low wing Nanchang CJ6A has two wing tanks but only a fuel on off valve. It however, has a small centerline collector tank that is lower than both wing tanks and from which the engine draws fuel.
Moderator
Nanchang CJ6A has two wing tanks but only a fuel on off valve
The danger is that an air lock can occur which will prevent fuel from reaching the engine. A similar situation can be experienced trying to start a heat soaked engine on a hot day.
§ 3.429 General. The fuel system shall be constructed and arranged in a manner to assure the provision of fuel to each engine at a flow rate and pressure adequate for proper engine functioning under all normal conditions of operation, including all maneuvers and acrobatics for which the airplane is intended.
.....Would assure that the engine would restart, as being stopped from a dry tank would be a "normal condition" for the purposes of certification. If an engine will not restart from a dry tank, the plane will not be approved.
This is a reason why some injected types (IO-520 and 550) are purged with the fuel pump prior to starting. If vapour has formed in the injection lines while it sat hot, that vapour is purged. Same thing would happen if you'd run a tank dry, or turned the fuel off.