Engine Roughness/Loss of Power

[Big Pistons Forever]

This thread is meant to compliment the one on the use of Carb Heat.

In flying training engine problems are usually presented as binary. Engine runs engine doesn't run. However the engine malfunctions that the average PPL is much more likely to actually encounter is a rough running engine and/or a loss of some engine power. What to do about this hardly ever seems to be covered in flight training.

I recently helped redo the emergency checklist for a local flight school and I addressed this issue in the non memory recall section. The intent is a "check" for the pilot use if he/she encounters an engine problem. It goes as follows

Engine Roughness/Reduction in Engine Power

-Carb heat.........................................Full On for at least 30 sec
-Engine gauges...................................Check
(Note if severe carb ice exists engine will initially run very rough until ice has cleared)

If problem persists

-Carb heat........................................Cold
-Mixture ...........................................Full rich then lean to max RPM

If problem persists

- Mags............................................Select right and left mag individually
(Note if engine roughness is more pronounced on one mag select the other mag or both, whichever gives smoothest operation)

----------------Land at nearest suitable airport------------------------

If problem persists

- Fuel selector.................................Left for 2 mins

If problem persists............................Right for 2 mins

---------------Land at nearest suitable airport-------------------------

In addition to to this I have emphasized the importance monitoring the engine instruments in flight. Instructors now periodically and without warning cover the oil temp/press gauges and make sure the students know where the needle is actually pointing. (In the green is not a good enough answer :ugh:).

Internal mechanical failures resulting in a total engine failure are the least likely cause of an engine failure but they do happen. The good news is there will almost always be some warning. Any internal misalignment or failure will almost always result in metal rubbing. This will cause a rapid rise in oil temperature with the oil temp gauge pegging at its maximum value. A dramatic drop in oil pressure will quickly follow. Any engine showing these signs should be presumed to be in danger of imminent total failure and appropriate actions to land ASAP should be taken. The only caveat is an open circuit in the oil temp wiring will cause the oil temp needle to peg at the highest temp. However in this case the oil pressure will be normal so it is likely just the gauge. However a landing at the nearest suitable airport would be prudent

[peterh337]

Of course the other reason for engine roughness might be the use of fine wire (iridium) spark plugs made by Champion which have contained defective resistors for many years - see the thread I started here a few weeks ago :)

On your last para, this is why I have two oil temp gauges and two oil pressure gauges. Getting a 2nd oil temp gauge installed is usually trivial; mine was done via an extra probe on the EDM700. Getting a 2nd oil pressure gauge installed is usually not trivial (on a G-reg) but is unquestionably a Minor Alteration on an N-reg if done right, and UMA (http://www.umainstruments.com/) make some nice compact (1.25") TSOd transducers and instruments for that.

I see proon has modified the rules under which it marks posts as edited. Previously one had ~ 1 minute to do edits; now it is zero.

[achimha]

That "in this case the oil pressure will be normal so it is likely just the gauge" case seems to be a standard thing that PPL students learn. I'm not convinced it's a smart thing to teach students. How likely is it and what is the chance of the pilot drawing the wrong conclusions because he remembers that the oil temperature gauge is very likely to fail?

Another case of rough running engine that most pilots are probably not aware of is mixture too rich. In hot and high conditions, you can often kill the engine by setting the mixture too rich. From my experience, students learn that in case of engine roughness, the mixture should be enriched.

[peterh337]

I don't think that - if your only engine instruments are oil temp and pressure - normal readings on those are a good guide to a good engine, because in a Lyco the oil pump is a constant volume (gear) pump which feeds a spring loaded pressure regulator valve which will maintain a constant-ish pressure over a fair oil temp range, and the oil temp itself will take a long time to rise, if at all, if there is a localised mechanical problem such a bearing about to seize.

[BackPacker]

Another addition to your checklist, BPF, might be the minimum RPM number at which flight is sustainable.

If RPM is higher than, approximately, 1700 RPM (assuming fixed pitch here), you can fly to the nearest airport (at approximately Vbg/Vy). If it's lower than that number, you cannot sustain flight and will have to prepare for an off-airport landing. But you might have a little engine power to control your descent.

Another thing is uncontrollable/runaway RPM, for instance due to a stuck or broken throttle linkage. Fly to the overhead of the nearest airfield, cut the engine with mixture and/or ignition and make a glide landing. To contain the RPM/speed in case of a runaway, initiate a climb or use steep turns. A runaway RPM can also be contained with very aggressive leaning. Yes, the engine will run rough, but you will be able to keep it below redline.

[AdamFrisch]

Magnetos can wreak havoc in the BOTH config, if one starts misbehaving. Can fire completely randomly. So, it can be better to run on one than use the false redundancy/safety blanket of both.

I've found that my oil temp meters either work or they don't. Abnormal readings are not the norm.

[172driver]

Abnormal readings are not the norm.

Well, if they were the norm, they wouldn't be 'abnormal' then ;)

Sorry Adam, couldn't resist.....

[piperarcher]

I have a related question. I was flying my Piper Archer 181 at 11,000ft and was levelled off, in clear air above clouds, with full RPM and sufficient leaninig. When I applied the carb heat, the engine began to run roughly. I left the carb heat on, thinking there might be a bit of icing. Once the carb heat was turned off, the engine was fine. Applying the carb heat again straightaway, the engine ran rough again. At the time the engine was near the end of its 2000 hour lifecycle and later was shown to have lost about 10% of its power over it's life. I was also pretty much near the service ceiling.

Was the roughness, due to the thinner air, possibly compounded by by the heat applied from the exhaust manifold? I wasnt overly concerned. We had to get a new engine later on anyhow, but havent since been up that high, so I dont know if my experience was 'normal' for the type of plane / height.

[peterh337]

The carb heat probably messed up your mixture setting.

At 11k you don't want to be running too rich.

[BackPacker]

My thoughts too. Did you adjust the mixture after applying carb heat? That might have solved the rough running.

Other than that - what was the OAT at FL110? If it's extremely cold, applying carb heat might actually bring the carb temps within the icing range. Although there will probably not enough moisture in the air at those OATs to actually cause icing.

[B2N2]

Engine running rough?
Fix it FAST!

F - fuel, change tanks or change mixture setting, or both.
A- air, carb heat or alternate air in case of engine with CS prop
S- spark, check magneto's L/R leave on L or R if condition simprove
T- technical, mechanical failure, throttle cable, mixture cable, oil on cowling or windscreen.. > divert or precautionary landing.

[Big Pistons Forever]

That "in this case the oil pressure will be normal so it is likely just the gauge" case seems to be a standard thing that PPL students learn. I'm not convinced it's a smart thing to teach students. How likely is it and what is the chance of the pilot drawing the wrong conclusions because he remembers that the oil temperature gauge is very likely to fail?

Another case of rough running engine that most pilots are probably not aware of is mixture too rich. In hot and high conditions, you can often kill the engine by setting the mixture too rich. From my experience, students learn that in case of engine roughness, the mixture should be enriched.

The oil temp gauge failing is more likely then the engine actually suffering a catastrophic internal failure. It would be a pity if a student on seeing a failed gauge, wrote off an airplane on an unnecessary precautionary landing, an event I know has happened. If the oil pressure is normal there is essentially no way you can have an above redline oil temp. Obviously you still land at the nearest suitable airport though.

This does beg the question of what is "normal" oil pressure and temperature. Another area that usually isn't addressed in flight training. Oil temp and oil pressure effect each other.

I you have just started your engine on a cold morning it would be normal to have the oil pressure every high, probably close to the upper redline limit with the oil temp at the bottom of the gauge. As the oil warms up the oil pressure will slowly reduce to a more normal mid gauge (ie 75 ish PSI) indication. However if you restart the engine after a short break on a 30 C day, you will should a very high oil temp and the oil pressure will probably be in the yellow arc at low RPMs. Therefore a low oil temp at start up on a cold day with low oil pressure or a very low oil temp after a short shut down on a hot day should be of concern.

I agree with your comment about the mixture which is why it is addressed in my checklist. Since the problem could be too lean a mixture as well as too rich a mixture it is best to start with full rich and then lean to maximum RPM.

[Big Pistons Forever]

Engine running rough?
Fix it FAST!

F - fuel, change tanks or change mixture setting, or both.
A- air, carb heat or alternate air in case of engine with CS prop
S- spark, check magneto's L/R leave on L or R if condition simprove
T- technical, mechanical failure, throttle cable, mixture cable, oil on cowling or windscreen.. > divert or precautionary landing.

I personally do not agree with this check.

The first thing that you need to do with a rough running engine is apply full carb heat.

[Big Pistons Forever]

I don't think that - if your only engine instruments are oil temp and pressure - normal readings on those are a good guide to a good engine, because in a Lyco the oil pump is a constant volume (gear) pump which feeds a spring loaded pressure regulator valve which will maintain a constant-ish pressure over a fair oil temp range, and the oil temp itself will take a long time to rise, if at all, if there is a localised mechanical problem such a bearing about to seize.

A friend of mine had a spun bearing in a Continental O 300 which has basically the same type of oil system as a Lycoming. He said the oil temp went from normal to pegged in less then 3 minutes with the oil pressure dropping to the yellow :uhoh:. He headed to the nearest airport and landed about 10 minutes later with the engine knocking badly. Halfway through the landing roll as the aircraft slowed the prop stopped :ooh:. The engine was removed for overhaul but was replaced as there were virtually no salvageable parts left.

[Big Pistons Forever]

Another addition to your checklist, BPF, might be the minimum RPM number at which flight is sustainable.

If RPM is higher than, approximately, 1700 RPM (assuming fixed pitch here), you can fly to the nearest airport (at approximately Vbg/Vy). If it's lower than that number, you cannot sustain flight and will have to prepare for an off-airport landing. But you might have a little engine power to control your descent.



A very good point although I would suggest for your average C 172/Pa 28 it will difficult to maintain level flight and do any manoevering below 1900 RPM so that is the value I teach my students to look for in the event of a partial engine failure, when they need to decide if they can continue or will be forced to land.

[Big Pistons Forever]

Magnetos can wreak havoc in the BOTH config, if one starts misbehaving. Can fire completely randomly. So, it can be better to run on one than use the false redundancy/safety blanket of both.

.

As a general rule engines should not be run at in flight power settings on only one mag for extended periods. If the problem is a fouled/failed plug in one cylinder then switching to the mag driving that plug will isolate the problem as that cylinder will have no plug firing and the engine will be extremely rough. So now your choice is to leave it on the other mag or go to both. My vote is go to both so that all the other cylinders get the benefit of having both plugs firing. In practice there will not be any significant difference in roughness with either the good mag selected or both. If the engine is much rougher on both then just the one then running on the one mag would be appropriate.

I once had a mag suffer an internal failure which massively advanced the spark. The engine instantly lost a lot of power and was extremely rough. As soon as I deselected the bad mag the engine ran normally so I diverted to the nearest airport and landed.

[B2N2]

I personally do not agree with this check.

The first thing that you need to do with a rough running engine is apply full carb heat.

Not arguing with your experience but this is 6 of one or half-a-dozen of the other.
If overly mixture was the culprit for the engine running rough selecting carb heat could cause it too stop.
But let's stop the discussion here, the point being that you need some sort of check/procedure memorized for these events.

FAST, AFeST, BUMP, BUMPFICH, GUMP, GUMPS, it's all trying to achieve the same thing.............memory items.

[piperarcher]

My thoughts too. Did you adjust the mixture after applying carb heat? That might have solved the rough running

I didnt. Next time if I do the same procedure, I will try that. Thanks.

Other than that - what was the OAT at FL110? If it's extremely cold, applying carb heat might actually bring the carb temps within the icing range. Although there will probably not enough moisture in the air at those OATs to actually cause icing.

From memory, it was probably about -5. I recall it was a fairly warm summers days with maybe +20 on the ground. Thanks to you and Peter for your replies.

[DeeCee]

'If the oil pressure is normal there is essentially no way you can have an above redline oil temp.'

I afraid that there is a way. I took off on a very hot summer day and climbed to 2000'. As I levelled off I noticed that the oil temperature was rapidly approaching red. I returned to the airfield and we found that the carb heat cable had frayed and stuck carb heat at about half. This was not noticable from the knob which was fully in.

[Big Pistons Forever]

'If the oil pressure is normal there is essentially no way you can have an above redline oil temp.'

I afraid that there is a way. I took off on a very hot summer day and climbed to 2000'. As I levelled off I noticed that the oil temperature was rapidly approaching red. I returned to the airfield and we found that the carb heat cable had frayed and stuck carb heat at about half. This was not noticable from the knob which was fully in.

What did the oil pressure gauge show ?

[DeeCee]

Can't recall that I noticed anything else amiss, although it may have been that I was fixated on the temperature. This was about fifteen years ago.

[Big Pistons Forever]

Can't recall that I noticed anything else amiss, although it may have been that I was fixated on the temperature. This was about fifteen years ago.

I would suggest that the oil pressure was probably lower then normal reflecting the loss of viscosity of the very hot oil and confirming that it was not an oil temp gauge problem, but reflected a real overheating situation.

I think this scenario is an example of the utility of a static RPM check on the takeoff roll. As soon as the throttle is fully in at the start of the takeoff roll if the engine RPM gauge is showing within the static RPM range then you have some assurance the engine is developing full power. If the carb heat is on most aircraft will not generate full static RPM.

(Note what I am taking about is not the redline on the RPM gauge it is the RPM the engine will show when at full power and the aircraft is stopped or moving slowly. It will always be less then the redline RPM and its value can be found in most POH's)