Near Engine Failure Tonight

steviedeviant

steviedeviant

Pre-takeoff checklist
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StevieD
This afternoon I was renting a Cherokee 140 just to do some touch n gos. I have my ppl and just wanted to get a little time in the plane this afternoon.

On the third and final leg, I was turning downwind in the pattern, pulled back on throttle to cruise and as I did it, the rpm dropped suddenly and settled around 1700 rpm. Normally in the plan opI would be around 2200 rpm. The engine was running a little rough. I attempted to push the throttle back up and even at full throttle, the rpm would not go above 2000. As I was about to abeam the numbers anyway, I pulled carb heat, fuel pump on, neither made no difference. I got the plane down with no problem other than admittingly a little nervous about the event. I did think maybe this is icing, but that didn't make a lot of sense..primer..mixture...nothing..all looked right.

So after landing, I was the only plane on the field, I did another run up, but the engine still would not get above 2000. Primer was locked...can think of anything else. At the time this happened I was on my final touch and go without any problems...so not sure what may have caused this....any guesses?

I called the flight school to let them know and they are obviously going to look into it and pull the plane off the line.

Anyway, it may have just been a pattern situation, but it reminded me to always stay cool and fly the plane.

I am so ready to buy my own plane as many of you know. I have got to get away from these old rentals.
 
Probably not the issue here, but wanted to say something about carb heat given the way you wrote about it.

Remember carb heat isn't an immediate fix, it has to melt some ice to work, which takes time, did you give it time? Carb heat because it enrichens the already rich mixture actually makes things worse at first....


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Could you have accidentally switched one of the mags off? Don't think it would make that much of a difference but just an idea.
 
Thanks for the reminder. In the Cherokee 140 there seems to be a little debate on the use of carb heat. I flew mostly in the 140 when I got my ppl, and my instructor always told me to use carb heat but I pointed out to him in the POH that Piper says only use if needed. He then pointed out to me that some FAA guideline stated to use carb heat even if the PoH stated otherwise. Anyway, I tuned the carb heat on because I was abeam the numbers by this point and still it didn't seem to make a difference other than to cause rpm to fall slightly more as it always goes anyway.
 
Grum.Man said:
Could you have accidentally switched one of the mags off? Don't think it would make that much of a difference but just an idea.
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No..I check that after landing though to be sure. but that is exactly what it felt like and it did cross my mind.
 
Losing an engine on downwind is probably the best time for it to happen. Glad everything ended up well.
 
steviedeviant said:
Thanks for the reminder. In the Cherokee 140 there seems to be a little debate on the use of carb heat. I flew mostly in the 140 when I got my ppl, and my instructor always told me to use carb heat but I pointed out to him in the POH that Piper says only use if needed. He then pointed out to me that some FAA guideline stated to use carb heat even if the PoH stated otherwise. Anyway, I tuned the carb heat on because I was abeam the numbers by this point and still it didn't seem to make a difference other than to cause rpm to fall slightly more as it always goes anyway.
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Safe to say it more than likely wasn't anything to do with carb heat. Keep in mind that engine failures are most likely to occur during power changes. All power changes should be a smooth and consistent application or reduction of power rather than an abrupt change. Not to say this had anything to do with this scenario, but it's something to keep in mind.
 
steviedeviant said:
Thanks for the reminder. In the Cherokee 140 there seems to be a little debate on the use of carb heat. I flew mostly in the 140 when I got my ppl, and my instructor always told me to use carb heat but I pointed out to him in the POH that Piper says only use if needed. He then pointed out to me that some FAA guideline stated to use carb heat even if the PoH stated otherwise. Anyway, I tuned the carb heat on because I was abeam the numbers by this point and still it didn't seem to make a difference other than to cause rpm to fall slightly more as it always goes anyway.
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What was the temp/dew point? Yeah once you out the carb heat on leave it on.... the pipers aren't all that susceptible but sounds like carb ice


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gsengle said:
What was the temp/dew point? Yeah once you out the carb heat on leave it on.... the pipers aren't all that susceptible but sounds like carb ice


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It's possible, but carb ice isn't just going to present itself upon a power adjustment.
 
You did all the correct things. Kept your head, fly the plane. Well done!

As for the RPM drop could be a number of things, but if it happened exactly when you pulled the throttle back I would suspect the cable attach at the carb has slipped. Could also be a coincidental problem with the carb float, or one mag has failed (did you do a mag check before shutting down?), or there is something obstructing the air intake (disintegrating foam air filter?). Might have been ice, but that usually clears pretty fast in a Cherokee on application of heat.
 
GRG55 said:
You did all the correct things. Kept your head, fly the plane. Well done!

As for the RPM drop could be a number of things, but if it happened exactly when you pulled the throttle back I would suspect the cable attach at the carb has slipped. Could also be a coincidental problem with the carb float, or one mag has failed (did you do a mag check before shutting down?), or there is something obstructing the air intake (disintegrating foam air filter?). Might have been ice, but that usually clears pretty fast in a Cherokee on application of heat.
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It did happen exactly when I pulled back the throttle. One of the instructors I know at the school thought maybe it could have been something to do with the cable so hopefully they will figure it out and let me know so I can learn more from it.

Hopefully the mechanic or flight school can give me a few ideas as well. Sounds like I did all I could. I will follow up with this thread as soon as I hear something back.



gsengle said:
What was the temp/dew point? Yeah once you out the carb heat on leave it on.... the pipers aren't all that susceptible but sounds like carb ice

Temp/dew point where almost the same. The storm had recently some through but it was about an hour before. So I know you are probably thinking like I was that it was carb ice. The only reason I think it wouldn't be the case is that the rpm only slipped exactly when I pulled back on the throttle. Also, since I landed with the carb heat on anyway, and then attempted to do another run up, the rpm never still got above 2000. That would have meant carb heat was on for at least a couple of minutes so by that point I would expect any ice to be gone.
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If you are running pretty rich to begin with and the carb heat comes on, you might get this exact situation. I had a carb heat cable break flight and the carb heat turned on causing about a 500 rpm drop since I was running richer than I should have been for the altitude. My clue however was when I pulled the carb heat on I got about a foot of cable with it. Leaning brought the rpm drop to only about 200 rpm as I flew to the nearest airport for repairs.

Brian
 
steviedeviant said:
Thanks for the reminder. In the Cherokee 140 there seems to be a little debate on the use of carb heat. I flew mostly in the 140 when I got my ppl, and my instructor always told me to use carb heat but I pointed out to him in the POH that Piper says only use if needed. He then pointed out to me that some FAA guideline stated to use carb heat even if the PoH stated otherwise. Anyway, I tuned the carb heat on because I was abeam the numbers by this point and still it didn't seem to make a difference other than to cause rpm to fall slightly more as it always goes anyway.
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My instructor said the same about carb heat until I pointed out the design of carb inlet and a lot of piper flyers will tell u carb heat close to the ground will do more harm than good. There is a video on YouTube recently made by friendlyskiesfilm that explains lot more. It's a non event now, since I have gotten a carb temp probe with JPI and never seen card temp below 46 degrees even when the situation is ripe for carb ice. It's a part of my downwind and base checklist to glance at the carb temp just in case.

Glad u made it down safely and kudos to you for handling the situation.


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Todd82 said:
26C dewpoint? Ugh. Definitely a juicy atmosphere. Just rained? Surprised you had the vis for VFR pattern work with 26/26.
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No issues at all from a weather standpoint. Everything was VFR, clouds at that point were pretty high - it has just rained about an our earlier, but everything passed - sure, there was moister in the air -.
I am in Alabama - Afternoon thunderstorms are the norm here and I waited for about a hour after it passed. Density altitude at the time was about 1500 and I remained in the traffic pattern the entire time.

Hopefully I will hear something back from the school that I rented on what they think, but the more I think about it, the less I believe this was any mixture or carb heat situation. From a carb heat standpoint, I was doing touch and gos and I had just turned off carb heat from the previous rollout after landing. So that means ice would have had to form in a very short amount of time - not saying it couldn't happen, but it just seems very quick. I don't believe it was a mixture problem at my DA. Lastly, the fact that is happened as I made the final adjustment for the downwind just seems fairly suspicious to me. and lastly, lastly....after landing, checking everything again, I tried to do a runup of the engine and it still wouldn't come back up on the ground...

Just leads me to believe it may be something mechanical.

I did receive a call from an instructor there who has told me that they just recently sent the oil out for analysis and while it came back clean, the oil has been darker than they would like. this is an older plan and the engine has gone through 2 rebuilds and is nearing its TBO again...so there could be something more this.

I appreciate everyone's feedback. I knew throwing it out to the board would give me some additional insight and I just wanted to see if there was something obvious that I could have missed.

Thanks,
SD
 
paflyer said:
Why would that have any affect on limited RPM? Restricted flow maybe?

Anyway, 600+ hours in PA28s, the only time I've ever applied carb heat is during the runup. :)
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The checklist for both rough running engine and an engine loss include switching / fuel proper tank.
 
Clip4 said:
The checklist for both rough running engine and an engine loss include switching / fuel proper tank.
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I didn't switch tanks, BUT, I am glad you pointed this out. Should I ever have a situation develop like this again, I will remember to keep that in mind. And to be honest, switching tanks didn't cross my mind, so that is a something I need to think about for just my own learning and self-evaluation.

I realize this wasn't a "big deal", but for me it was at least a learning experience from the standpoint of how I reacted. For that brief moment, I was a very nervous, and I think I covered most of the items to check, but switching tanks wasn't one of them. Thanks.
 
In a Cherokee you should turn on the fuel pump as well, but that is also on the before landing checklist so you probably had it running already. Not that engine driven fuel pump failure is a likely explanation for your situation, just a possibility that the "WTF is the engine doing now?" checklist will rule out.
 
Never needed or used Carb heat in a couple hundred hours of flying a Cherokee in the North East That said, think about water, does the plane have a power flo exhaust? A similar thing happened to me and a Gary Shelby from this board. One fine day we took off in his 140 climbed turned downwind climbed out and the engine RPM dropped and ran somewhat rough. We monkeyed with the throttle and found it did better when we pulled the throttle out a bit so we left it out ( actually did worse when we advanced throttle) We turned back to the field and landed.

We could not recreate the situation on the ground but grounded the plane till the mechanic took a look. We too thought carb ice because we could not create it. Turns out Gary has a power flo. Somehow when it rained ( his plane is tied down outside) the installation on his 140 allowed water to run down the power flo exhaust system and I believe pool at or in the air intake. When we climbed and had full throttle the angle and i guess airflow caused the water to be ingested into the air intake. He had a sharp mechanic figure it out who contacted the company and if I recall correctly it was not the first time this happened. They provided him with some sort of fix and it haas not happened again. I think the difference is your engine may not have run rough just a drop in rpm is that correct? Best of luck I hope they find the answer.
 
Is it possible the throttle movement dislodged some ice?


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Ryanb said:
Keep in mind that engine failures are most likely to occur during power changes.
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OWT? I hear pilots and CFIs repeat this, but have never seen data to support it.
 
Ryanb said:
Safe to say it more than likely wasn't anything to do with carb heat.
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Why not? This is EXACTLY the circumstances one expects to find carburetor ice. You need to turn on heat AND increase the power (not seeing whether the pilot said he did that) and WAIT.
Keep in mind that engine failures are most likely to occur during power changes.
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Bullpoop.
However, another possibility is too much heat. People always want to worry about shock cooling and carb ice when there are a lot of things from the valves and cylinders themselves to the coils in the mags that can be screwed up by excessive heat. Lots of max power, high angle, climbs in pattern work can indeed spur this.
The real insidious problem is one that goes away after landing. Easier to fix the ones that are persistent.
 
I surmise that the nut holding the throttle control arm on the carburetor finally came loose when you reduced power for the last landing.
Still holding the arm in place but loose enough that the full range of movement was compromised...
 
Ryanb said:
Keep in mind that engine failures are most likely to occur during power changes. All power changes should be a smooth and consistent application or reduction of power rather than an abrupt change. Not to say this had anything to do with this scenario, but it's something to keep in mind.
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I agree that power changes should be smooth and not abrupt, but engine failures being more likely to occur during a power change is nothing more than a wives tale.

Think about this, a very large power change on a normally aspirated engine occurs when the throttle is advanced from near ideal to 100% power on take off. Where are all the "My engine failed before I got off the ground" stories?
 
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flyingron said:
Why not? This is EXACTLY the circumstances one expects to find carburetor ice. You need to turn on heat AND increase the power (not seeing whether the pilot said he did that) and WAIT.
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You would expect to bring the power back on downwind and suddenly carb ice occurs? Carb ice doesn't happen that quickly, so no it's not EXACTLY the circumstance that one would expect carb ice.
flyingron said:
Bullpoop. However, another possibility is too much heat. People always want to worry about shock cooling and carb ice when there are a lot of things from the valves and cylinders themselves to the coils in the mags that can be screwed up by excessive heat. Lots of max power, high angle, climbs in pattern work can indeed spur this.
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Sorry you disagree. Abrupt power changes such as advancing the throttle or reducing it, cause all of those moving parts to change speeds faster than inertia and kindness would like them too. Does every engine failure occur during a power change? No. But the likelihood that a problem does arise increases exponentially during throttle changes.
 
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Clip4 said:
I agree that power changes should be smooth and not abrupt, but engine failures being more likely to occur during a power change is nothing more than a wives tale.

Think about this, a very large power change on a normally aspirated engine occurs when the throttle is advanced from near ideal to 100% power on take off. Where are all the "My engine failed before I got off the ground" stories?
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Perhaps, but my one engine failure did occur with a power reduction, so hmmm


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Clip4 said:
Think about this, a very large power change on a normally aspirated engine occurs when the throttle is advanced from near ideal to 100% power on take off. Where are all the "My engine failed before I got off the ground" stories?
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I thought about it and here's my reply. Rapid power changes 'can' cause a pre-existing engine component that has a weakness to reach the point of failure. During the takeoff phase the engine transitions from a negative to positive power output very quickly, especially if the throttle is increased abruptly. If there is a component weakness in the engine, it may take a few seconds or even minutes for it to pose a problem. It would be nice if this happened during the ground roll, but as we have witnessed with many failures during the initial climb, that's not always the case. Again, is this the reason for all engine failures? No. But it is a very real factor to consider. Smooth power changes are ideal.
 
As long as we're speculating, my WAG is that a piece of muffler baffle broke off and clogged the tail pipe. That would also explain not being able to make full RPM when he ran it up after landing.
 
Ryanb said:
Keep in mind that engine failures are most likely to occur during power changes. All power changes should be a smooth and consistent application or reduction of power rather than an abrupt change. Not to say this had anything to do with this scenario, but it's something to keep in mind.
Click to expand...

Ryanb said:
Sorry you disagree. Power changes such as advancing the throttle or reducing it in an abrupt manner, cause all of those moving parts to change speeds faster than inertia and kindness would like them too. Does every engine failure occur during power changes? No. But the likelihood that a problem does arise increases exponentially during throttle changes
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"Most engine failures" and "increase exponentially during throttle changes"???

If this were the case, wouldn't students in trainers be littering the airport grounds as these planes spend their days being ham-fisted up and down in an endless string of touch and goes / simulated power failures??

Abrupt changes are hard on balance weights and should be avoided. Having the prop drive an engine can cause ring flutter. Neither cause engine failures during a power change.

Other than snapping a throttle linkage or cable, I am still trying to comprehend what other failure modes will exponentially be more likely to occur.

Help us here and name some components that come from together and and cause exponentially more engine failures during a power change?


[edit]. Never mind. I see you have already responded while I was typing and I don't want to pile on. Just hate the proliferation of old wives tales that occurs and carries on to the next generation.
 
Ryanb said:
You would expect to bring the power back on downwind and suddenly carb ice occurs? Carb ice doesn't happen that quickly, so no it's not EXACTLY the circumstance that one would expect carb ice.
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You're deluded. Carb ice CAN happen that quickly. Yes, you can get carb ice showing in a gradual decrease in power but you can also see it as a sudden choking of the engine. I've seen it both even in my old GO-435 and with the old O-300 in the 170 I used to fly.

Abrupt power changes such as advancing the throttle or reducing it,
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I don't disagree that you want to slam the throttle/prop control with an abrupt change but that's NOT what you said.
You said "Keep in mind that engine failures are most likely to occur during power changes." That is nonsense.
 
flyingron said:
You're deluded. Carb ice CAN happen that quickly. Yes, you can get carb ice showing in a gradual decrease in power but you can also see it as a sudden choking of the engine. I've seen it both even in my old GO-435 and with the old O-300 in the 170 I used to fly.
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Based upon the OP's description of what happened, Carb ice doesn't sound likely. Carb ice is a gradual condition that strangles the engine. I can't imagine within no more than a second and a half of pulling the power on downwind that carb ice would present itself. It just doesn't sound likely. Not going to argue that it didn't occur quickly in your own airplane, but that isn't the norm.

flyingron said:
I don't disagree that you want to slam the throttle/prop control with an abrupt change but that's NOT what you said.
You said "Keep in mind that engine failures are most likely to occur during power changes." That is nonsense.
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So when do most engine problems occur? During takeoff and the decent to landing phase, both require power changes (explained more in #33). Again, I'm not here saying that every engine failure is due to this, but it is certainly a factor that can contribute.

BTW, it's not just a wives tale.
 
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Just repeating your opinion doesn't make it true. Carb ice onset is not necessarily gradual. AOPA and the FAA and every other document on the subject doesn't support your argument. In fact, reduced power operations is a contributing factor. See AC 20-113,

Post #33 lends nothing to this other than the fact that you're arguing coincidence which even then isn't all encomapssing. A lot of power failures occur during high performance operations (climbs on takeoff) when the throttle has remained firewalled. There's no statistical amount of failures due to power reduction on approach. So it would probably be more correct to blame things on high power, high temperature operations than the fact that someone moved the throttle recently.
 
flyingron said:
Just repeating your opinion doesn't make it true. Carb ice onset is not necessarily gradual. AOPA and the FAA and every other document on the subject doesn't support your argument. In fact, reduced power operations is a contributing factor. See AC 20-113,

Post #33 lends nothing to this other than the fact that you're arguing coincidence which even then isn't all encomapssing. A lot of power failures occur during high performance operations (climbs on takeoff) when the throttle has remained firewalled. There's no statistical amount of failures due to power reduction on approach. So it would probably be more correct to blame things on high power, high temperature operations than the fact that someone moved the throttle recently.
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Okay Ron. Thanks for your input, I certainly don't expect everyone to share the same viewpoint.
 
Ryanb said:
Okay Ron. Thanks for your input, I certainly don't expect everyone to share the same viewpoint.
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Viewpoints that don't have data to support sound an awful lot like old wives tales.

They sound logical enough to continue spreading as gospel, but no one can seem to find the facts behind them.

No offense meant.
 
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