Rough Running Engine

[fireflybob]

Which is why PA38s have a button you have to push to turn the fuel off - otherwise it will only go on Right or Left. A feature which long ago should have found its way into the PA28, if you ask me.

All the PA28s I have ever flown have a catch to help prevent inadvertant turning of the fuel selector to the OFF position.

[BackPacker]

I was on my first ever flight in a Robin DR200-160, after having flown the -120 and the -135CDI, and the R2160. But all of those had a single fuselage fuel tank, while this -160 also had two ferry tanks in the inboard section of the wings. We had flown on left for a while, then on right, and the remainder of the flight was to be on the main tank. So I twist the fuel selector to, what I thought, was the "main tank" position (arrow pointing forward). As it turned out, this was the "off" position. Arrow pointing backwards was the main tank.

Isn't there some sort of certification requirement that specifies that knobs, selectors and such, to the extent possible, should have "up" or "forward" meaning "good", "fly", "go faster" and "down" or "back" meaning "bad", "stop", "land", "go slower"? Plus, if you want to do something that might be really stupid in-flight (such as shutting off the fuel completely), shouldn't there be some sort of guard so that you cannot do this by accident?

Fortunately the pilot who accompanied me spotted my error in time.

tmmorris, the PA28 does have a little guard built-in into the fuel selector so that you cannot accidently turn it off. In fact, the first time you deliberately want to turn it off (on the ground) you've got to look carefully at how to place your fingers so that you can push the guard out of the way and turn the selector at the same time. At least, this is on all the PA28s I have flown (so far the -161 model only).

[Mike Cross]

Dunnit as well!

Beagle Pup has the fuel cock on the floor in front of the seat squab. Tapered pointy thing on top. Point it in the direction of the tank you want or forward for both, rearward for off. Needless to say I'd switched form "Left" to "Both" but had ended up with it pointing backwards rather than forwards.

One of the reasons not to change tanks near the ground or immediately before take-off or landing.

[SNS3Guppy]

Isn't there some sort of certification requirement that specifies that knobs, selectors and such, to the extent possible, should have "up" or "forward" meaning "good", "fly", "go faster" and "down" or "back" meaning "bad", "stop", "land", "go slower"?

No. You'll find quite a disparity between makes and models, and even the same type aircraft from the same manufacturer where different customers have different requests. In some cases, the switch positions can be exactly opposite...even on the same model aircraft.

Plus, if you want to do something that might be really stupid in-flight (such as shutting off the fuel completely), shouldn't there be some sort of guard so that you cannot do this by accident?

Not necessarily. Otherwise we'd have a lock on the mixture (some have a quasi-lock with a vernier control, others a simple metal tab, others none). Locking out the fuel shutoff could hurt or kill you in an emergency.

The first thing that should come as an automatic response is to unload the wings.....push forward hard. The article makes a point of stating how much you actually have to push, and the amount of horizon which fills the screen - it varies for each aeroplane but rule of thumb is that you go from 2 thirds sky filling the screen (on climb out) to 2 thirds ground filling the screen (at best glide).

This is unnecessary in an engine out or in a stall condition. The aircraft will continue to descend at it's trimmed airspeed, in fact. In most light airplanes, your climb speed is very close to your glide speed. If you're trimmed for the climb, you're trimmed close to the glide. In general terms, your best glide speed will closely approximate your sea level best rate of climb speed (Vy), and your minimum sink glide speed will closely approximate your sea level best angle of climb speed (Vx). If you're trimmed for one of these speeds on the climb, a power loss will result in a trimmed descent at that speed if you don't get involved (i.e. pulling back and interfering with the airplanes ability to do it's job...remain stable).

Inexperienced flight instructors scare students by teaching agressive pushing in stall training; it's not necessary. The difference between stalled and not stalled is less than a degree in angle of attack...something you can't see. If you're holding back pressure to stall the airplane during practice, for example, very slight relaxation of the back pressure is all it takes, and you can recover easily enough with the nose on the horizon...no need to fill the windscreen with sky, or ground for that matter. Likewise during an engine failure; you're entering a glide, not divebombing the enemy. Don't get in a rush to be too agressive with anything.

So far as preventing a spin...that's preventable by continuing to fly the airplane. Don't let it spin. Airplanes don't spin on their own...they need to be shown the way. Don't do that.

[bjornhall]

My take on it...

Slight roughness, gradual onset, no power decay?
- Check magnetos L/R, if significantly worse on either, suspect fouled plugs. Lean to proper cruise setting, wait for plugs to unfoul themselves (should take a couple mins). Would head for an airport or at least fly to/remain over suitable terrain for a forced landing at this stage while waiting for the plugs to clear, "just in case".

Sudden onset of significant roughness, or as above but didn't clear after a few mins?
- Check magnetos L/R, if significantly worse (or engine stoppage) on either, suspect magneto failure. Procede to nearest suitable airport; use single magneto if needed.

No change with magnetos L/R?
- If manual alternate air available, pull it.
- If fuel pressure fluctuations (check "fuel flow" gauge), fuel pump on.

None of the above solved it?
- Something's the matter; procede to nearest suitable airport while remaining over suitable terrain. Vary mixture, trying to find a setting that minimizes roughness (if that results in an unusual mixture setting, something is still the matter).

ATC?
- If I need their help for any reason (my prefered route takes me through controled airspace, I'm out over the sea and need to be rescued in a hurry if the engine was to fail, or some such), make a Pan Pan call.

That's how I'd do it!

[Maoraigh1]

Carb float leak

I've read of a leaking carb float causing too rich rough running. Carb heat warmed the air in the float, causing expansion, which pushed fuel out, restoring float buoyancy, and engine ran O.K. This lead to carb ice being assumed to be the problem. Cold air lead to contraction of the vapour in the float, and more fuel entered the float, until the mixture was so rich the engine lost too much power for the aircraft to remain in flight. The pilot made an off-airfield landing, blaming carb ice.
Would leaning the mixture work with a sinking carb float?

[SNS3Guppy]

I've read of a leaking carb float causing too rich rough running. Carb heat warmed the air in the float, causing expansion, which pushed fuel out, restoring float buoyancy, and engine ran O.K. This lead to carb ice being assumed to be the problem. Cold air lead to contraction of the vapour in the float, and more fuel entered the float, until the mixture was so rich the engine lost too much power for the aircraft to remain in flight. The pilot made an off-airfield landing, blaming carb ice.
Would leaning the mixture work with a sinking carb float?

Sounds good on paper. However, the carburetor heat doesn't come near the float, and doesn't warm it; carb heat is used to adust the tempeature of the induction air...not the carburetor, not the float bowl, and not the float. The float is sealed, not full of fuel, and the temperature of the float doesn't make any difference in it's ability to function. Regardless of it's temperature or that of the fuel, it should always float. The function of the carburetor float is only to stop fuel flow into the float bowl, when it reaches a predetermined level, and it does this by action of a needle valve actuated by the float. The float bowl, in turn, only serves as a holding resorvoir, a small "header tank" if you will, which supplies the main and idle jets.

Worse case senario, you have a float which fails and leaks...preventing it from floating on the fuel and shutting off fuel flow to the carb float bowl. The carburetor floods out.

A certain amount of air above the fuel in the float bowl is required, as the main jets work based on differential pressure between the carb throat venturi, and ambient air pressure/fuel pressure...the ambient pressure supplied by venting the float bowl. Flood it and you can have an engine stoppage, or supply enough fuel uderpressure adn you can flood out the carb and engine...and have either a fire or an engine failure.

Can you prevent it by leaning the carburetor? Possibly, but don't count on it. You can go to cutoff on the mixture and still have a fire hazard or flood problem. Where it's usually noticed is when you approach the airplane to preflight...the float has sunk and you'll see fuel leakage down the nosewheel or through the bottom of the cowl, with stains or wet goo present depending on the nature of the leak, the ambient temperature, etc. In flight, you're not going to know the float has sunk; you may have a rough engine, you may not.

[SoundBarrier]

I had the engine in a C182 do horrible things once, it surged twice and then stopped making noise. I managed to get the engine going again, but as said before...

Step 1 :- Profanities.
Step 2 :- Procedures as per the POH

If the rough running does not go away, I would start with the mags and then move onto the fuel. Just remember, when playing with the fuel it can take a little while for some fuel to come through if you've run a tank dry or had an issue with a lack of fuel for some reason.

[kiwi chick]

SoundBarrier, you beat me to it!

From experience:

1) Say "fcuk"
2) Carb heat
3) Mag check
4) Fuel - check pressure & tanks
5) 7700
6) land

(I got priorty cleared to land at wellington, no less than three Air NZ planes lined up waiting to enter and roll while I trucked on in in my little PA-28... I still remember one of them responding to ATC's "hold at Alpha for light aircraft on priority" with "What??" )

[SoundBarrier]

Kiwi Chick :-

For more detail -

1) "Oh, Fcuk!" (Turns to pax and says, "No everythings fine, just a little glitch!)
2) Push and pull levers and switches and things while sweating like a sprinkler at 500PSI
3) No change
4) "Oh, Fcuk -Fcuk"
5) Eat part of your chair with your buttocks (I didn't know I was THAT hungry)
6) Engine roars back to life - "I Love you plane!" you scream, with your pax looking rather perturbed
7) Land safely at nearest airfield - taxi direct to pub to consume much alcohol.
8) It's almost midnight and you go back and help your pax out the plane 'cos you forgot they were there!

[kiwi chick]

"I Love you plane!" you scream

That is so funny!!!

I was asked by ATC if there was anything they could do to help. (WTF??? Are they gonna come up here and check the engine??)

I said "yes thanks, have a bourbon waiting for me when we land".

But they didn't find it half as funny as I did (in my fear-induced delirious hysterics)

[SoundBarrier]

Yeah ATC do loose a sense of humour at times, bless 'em. My best was when a newbie controller at a local field lost the plot with 11 planes in the circuit 5 of which were on final, hi pipes on the airwaves and says...

"All aircraft on final....SCATTER!"

Everyone assumed an uncontrolled airfield for the next 30 mins, it was so funny! Everyone was giggling on air!

[kiwi chick]

Hahahahahaha!! What airfield was that?

[SoundBarrier]

FVCP - But many years ago.

[llanfairpg]

Bob--as you are one of the most experienced pilots and instructors on here my action would be to say

"You have control"

[fireflybob]

Bob--as you are one of the most experienced pilots and instructors on here my action would be to say

"You have control"

I like your style!!

[First_Principal]

In case it helps anyone else I had just this scenario (rough running, losing power etc) in a small Cessna. It was a little irregular insofar as it would come and go a bit and the rough running itself wasn't constant .

Being a bit of a spanner I could tell that as it wasn't regularly missing it was less likely to be ignition. This was more of a 'feel' thing but FWIW the logic is that a fouled plug or failed valve/piston/cylinder would be more likely to have a regular miss than say carb ice. If you want an example try pulling a plug lead off a running 4 or 6-cyl car engine sometime.

Anyway I did the first thing one should do and pulled the carb heat, miraculously it made quite a difference ... for a short period of time after which the problem returned. Bearing in mind this was a hot, dry, day with temp/dewpoint miles apart (I checked!) it seemed rather unlikely to be real icing but I ran with that view for a bit.

After a while (probably not that long although it seemed ages) I decided it was more likely to be a mechanical problem with the carb and/or air intake. Careful manipulation of the carb heat control would restore the engine for a period of time, after which it would return to the original problem. At times I had to mess with it continually, other times it would operate ok for several minutes.

Given I was some distance from a 'drome, over rough(ish) terrain, or sea, I elected to continue on rather than attempt a precautionary landing. It would have been do-able, if necessary, in some places but at its worse the engine would run a max of 2200/2300 rpm (with EGT vy hot) which was enough (just) to maintain a couple of thousand feet.

Incidentally I also checked the fuel tap was in the correct position and tried running on individual mags once I'd established an ability to keep going, at least for a bit. What I didn't do was mess with the mixture, my logic being that I didn't want to play with anything more than was necessary - especially carb related - in case I exacerbated the situation and/or introduced another problem.

Eventually I landed and a subsequent check showed that the carb intake flap select lever cable clamp had become loose meaning that the engine was in fact alternating between full carb heat to normal air intake and something in between from time to time. By moving the carb heat control I was occasionally able to move the flap when the clamp momentarily grabbed.

The crunch to this long-winded tale is in the decision-making really, IMO. Not every situation is the same and, if possible, some logic should be brought to bear on the issue. If the fan stops completely then between soundbarrier & k1w1 chick you've got it mostly covered <grin> but if it's still running, albeit roughly, then there could be other options. Most important, methinks, is to DO ONE THING AT A TIME, and, if possible, give that action a few moments to see if it makes a difference. If it is icing carb heat won't necessarily work immediately, in fact it could even become worse momentarily, likewise changing tanks or whatever could take a few moments to make a difference. The main thing is not to panic (yeah ) and start pulling and pushing things haphazardly. If in the end nothing works and you've insufficient power to keep in the air then you better go through the drill and pick your landing spot smartly, however if you are able to keep it going, at least for a bit, it widens your options considerably - at least insofar as where you're going to land. This could make all the difference, particularly if you're over inhospitable terrain.

No doubt there's other things I could say from this experience, I'm not convinced myself that I made the right decision - perhaps I should have landed immediately, perhaps I should have tried the mixture too (theoretically at least it may have helped), but I've lived to tell the tale which has allowed me to ruminate about the situation somewhat. I don't think I'll ever quite reach a conclusion, mostly in fact I think I didn't do quite what I should have, but I'm not sure if thinking this would actually help another time because the chances are it would be a different situation with different parameters to deal with. So perhaps the moral of the story is to by all means follow the drill but don't do so blindly, do it deliberately. Particularly if you've height and/or partial engine in hand try and think things through both in terms of what you're about to do and if perhaps you (or pax!) have just recently done something that may have introduced the problem...

Finally, once down, don't be afraid to make an arse of oneself on proon and tell all - it could well help someone else one day as could (some of!) the subsequent comments. Bring 'em on !

[ShyTorque]

Beagle Pup has the fuel cock on the floor in front of the seat squab. Tapered pointy thing on top. Point it in the direction of the tank you want or forward for both, rearward for off. Needless to say I'd switched form "Left" to "Both" but had ended up with it pointing backwards rather than forwards.
One of the reasons not to change tanks near the ground or immediately before take-off or landing.

Yes, I visited EMUAS where I used to instruct and asked where "my" Bulldog was. The ground crew chief led me by the arm to a pile of metal at the back of the hangar.... a AEF pilot got the fuel selection badly wrong and the engine stopped during the climb.

[fireflybob]

Of course it's always possible to turn selectors in the wrong direction even when safety devices are fitted.

However when you turn the fuel selector "OFF" after engine shutdown you are practising how to do so (as well as ensuring that it is physically possible to select "OFF"). It seems to be the practice of some operators to leave the fuel selector ON after shutdown, unless perhaps it is the last flight of the day.

I have flown with some pilots on the PA28 who were not aware of how to turn the fuel selector to the OFF position because there were not used to turning the selector to the OFF position.

[llanfairpg]

Exactly our thinking on the C152/0. I have even see fuel cocks drilled and wire locked on!!!!!