Engine dies during runup

[Chris_Ford]

After reading the "Overly Conservative Pilots" thread, I've thought about how I often times am too conservative. So I pose a question to you, the loyal JCers out there.

You're doing your runup and when you bring it back to your idle check, the first few times RPMs drop down to ~300RPM, then after revving the engine back up and bringing it back to idle, the engine flat out quits.

This is a valid reason to put the plane down right?

My thinking is that perhaps it's just a function of airflow over the prop and that in the air, it wouldn't fail, but I wouldn't want to take that risks... Just curious to see if you guys out there disagree.

This, unfortunately, has killed any opportunity to fly today, the first 10SM CLR day (with no haze) we've had here for a bit.

Edit: Also, can I log the .3 since my intentions were on flying the airplane?

[MikeD]

Could be throttle linkage out of rig, or maybe a problem with the fuel control.

What's the nature of, or priority of, the mission you're launching on?

Answer that, and you have your answer.

[Chris_Ford]

Exactly what happened... First flight with a new student = low priority. Flying it over to get fixed = important.

Sometimes it's just nice to have someone agree with you that you made the right decision... Call me insecure if you must

[DE727UPS]

"Also, can I log the .3 since my intentions were on flying the airplane"

Yes.

Were you in a 152? What number is in your POH for minimum idle rpm?

[Pilot Hopeful]

Logging the 0.3?

My read of FAR 1.1 "Flight Time" would seem to indicate no...

...unless you were able to takeoff and make a subsequent landing.

Is there another regulation that would dictate otherwise?

[zerouniform]

Make sure you don't have the carb heat (if any) on while you idle checked. There's an article in a past AOPA Pilot magazine about that; I can't remember which month it was in, but within the past 6 months probably.

What did the mechanics say about it, if anything?

[Chris_Ford]

Minimum idle is 575, the plane was idling at 300, then after about a half second of it, it died.

Maintenance men (30 miles away = free 1.5 trip in a 40 mile arc around Indianapolis ) said it was more than likely a problem with the servo and he suggested that I break it before its 100 hour (which is going to occur tomorrow morning)... I'm not really sure how to break the servo... hell, I had to google "servo" to see what it looked like

[MikeD]

[ QUOTE ]
Exactly what happened... First flight with a new student = low priority. Flying it over to get fixed = important.

Sometimes it's just nice to have someone agree with you that you made the right decision... Call me insecure if you must

[/ QUOTE ]

Once you can answer the "is it mission essential?" question, then the decision becomes easy; especially for 95% of civilian operations. When reading the thread I posted about overly conservative pilots, keep in mind the pilots, as well as the type of operation, I'm ranting about.

[kellwolf]

Flight time is counting as time with the intention of flight. He intended to fly until he found a problem. So, I guess TECHNICALLY don't log the time taxiing back?

[E_Dawg]

You technically can log the whole thing but it's kind of lame.

I have had fuel injected engines tend to idle rough and at such low RPMs that the engine seems it will die. I've even had engines quit on me in the runup during the idle check in the past (mainly with the fuel injected lycomming 172 engines in hot weather).

Try turning on the fuel pump to see if you can reduce the roughness and tendency to quit at idle. Also try leaning the mixture for the idle check, otherwise the excessive richness of the engine especially near idle may cause it to run rough.

I have a question for you: why would you cancel the flight with the student but then go fly the airplane anyway? You must have cancelled the student because the plane was unsafe but then why did you fly it? Of course by flying it later you must have thought it was safe so why did you cancel the student? Just things to think about...

[DE727UPS]

You still didn't say what kind of plane it was. I'm just curious. To me, it sounds like a carb problem. You can adjust the idle at the carb. Also, there is nothing inside a carb called a servo. I wonder if the mechanics are joking with ya....that would be pretty funny. What if they had said it was the flux capacitor?

[Doug Taylor]

And also, how much flight line did you have left? Next time it fails, ask the mechanics to check it, and if it still doesn't work, try a little prop wash.

[BrettInLJ]

[ QUOTE ]
Make sure you don't have the carb heat (if any) on while you idle checked. There's an article in a past AOPA Pilot magazine about that; I can't remember which month it was in, but within the past 6 months probably.

What did the mechanics say about it, if anything?

[/ QUOTE ]

Why is this? I was trained to pull out the carb heat on an idle check because you will typically do this on approach to land. I would not fly the plane until the cause was found.

[Chris_Ford]

C172S, fuel-injected. Thus there is no carb, and thus there is a servo (in the fuel injection system).

C/o Purdue: www.tech.purdue.edu/at/Courses/at403/Fuel_Metering_Systems.ppt

[ QUOTE ]
The regulator consists of an air diaphragm and a fuel diaphragm on a shaft with a ball-type [b]servo[b] valve in the metered fuel passage to the flow divider.

[/ QUOTE ]

And Doug......

As for the "if it was enough to cancel with your student, why did you go out and fly it" question... Well the fact of the matter was that when I was flying the thing alone, I'd rather not put a student in a situation where an engine failure is possible (at least, more probable than it normally is), especially on their first flight. As for me flying it on my own to get it fixed afterward, I realized that it was probably best not to bring it back to idle for very long, and kept it a bit above idle on the flight, and I was ready to put it in a field if need be.

Basically, it comes down to "I don't want to endanger anyone else's life just to make an extra $20" with the corollary: "I don't want to lose a complete day of work because of a relatively minute problem".

[project7]

[ QUOTE ]
Why is this? I was trained to pull out the carb heat on an idle check because you will typically do this on approach to land. I would not fly the plane until the cause was found

[/ QUOTE ]

I had an examiner show me this on a checkride. Makes sense to me.

[Chris_Ford]

Whoa, I need to learn how to close my tags and/or preview my posts

[zerouniform]

I would talk to a mechanic before I talked with an examiner on pulling the carb heat out on idle check. I'm sure every mechanic has their viewpoint on the matter, and the one I talked to said not to do it. Also, as I said before, there was an article in AOPA Pilot that said the same thing.

No need to get your panties in a bundle.

[Tim06]

Did you lean out the mixture if it was hot outside?

[Chris_Ford]

No I didn't, but it was ISA+5 or so... not really "hot" compared to what we usually get in the summer.

[MikeD]

[ QUOTE ]
Basically, it comes down to "I don't want to endanger anyone else's life just to make an extra $20" with the corollary: "I don't want to lose a complete day of work because of a relatively minute problem".

[/ QUOTE ]

How did you know it was minute if you dind't know what was causing the problem?

You've only got one engine up there. Flying with a known problem like that, to where you don't know the background of what's causing it, could buy you a 14 CFR 91.13 violation from the feds, were you to have to end up forced landing the thing somewhere.

[CFIse]

[ QUOTE ]
C172S, fuel-injected. Thus there is no carb, and thus there is a servo (in the fuel injection system).


[/ QUOTE ]

Known problem - there's Cessna guidance out on this that says something like "you get to adjust the throttle linkage twice in 12 months - then you have to replace the servo." or something like that.

It's a pain.....