Aborted takeoff, engine not producing full power

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Johann

Pre-takeoff checklist
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Johann
I was taking two friends up the other day. The plane was a C172R, so fuel injected.
It was pretty cold, I would say low 20s.

Engine started with no problems, didn't even take too much cranking, started right after a couple of revs.
Run up seemed normal, 1800 RPM, magneto drop normal and within range.

As I start my takeoff roll I do the usual checks. RPMs are reading 2000. I decided to abort the takeoff. It's funny, thinking back I feel like it took a minute from noticing to making the decision, as in I thought about the options, looked again to make sure I'm not looking at it wrong, thought "no, it's not in the green arc even, I'm reading it right", and so on.
Obviously it was much faster than I remember it, otherwise I would have gone past the edge of the runway, and I just rolled out at taxi speed on the same exit I usually use at landing.
I told the tower I was aborting for engine problems, they asked if I needed assistance, I said no thank you, and they gave me taxi instructions back to the ramp.

When I was past the hold short line I couldn't resist and I held the breaks and gave it full power. Still 2000.
If you look up disappointment in the dictionary, you'll find a picture of my two passenger's faces right there.

The FBO grounded the plane and the maintenance guy said he was going to look at it.

I called later and asked, out of curiosity, what they found. They said an instructor took the plane later and found nothing wrong with it.

I did notice that the throttle was a little hard to operate, but as I don't usually fly that plane I'm not sure if this is normal.

Any idea what could have caused this? Maybe too cold and the oil was not hot enough?
From start to takeoff it was probably ten minutes. Also an identical plane to this one started engine a couple of minutes after me and I saw it taking off right after me, but I think that one was flown recently so maybe it wasn't that cold.
 
Sounds like maybe you didn't get the throttle all the way forward, and that could have been due to cold, or it could be that the throttle was stuck, maintenance guy fixed it by checking it.

Regardless, your decision to abort the flight when you didn't get the results you were expecting was a good one. Nice job.
 
They would have been more disappointed if you had gone off the end of the runway or failed to climb over an obstacle.

I rejected two rental planes in one day. One at the runup, the other during the preflight insp. Either one "probably" would have been OK, but I wasn't about to find out.
 
TMetzinger said:
Sounds like maybe you didn't get the throttle all the way forward, and that could have been due to cold, or it could be that the throttle was stuck, maintenance guy fixed it by checking it.

Regardless, your decision to abort the flight when you didn't get the results you were expecting was a good one. Nice job.
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Concur with Tim. Also, with this engine, cold oil is not going to result in low RPM.

In any event, you did wait for the oil temp to get up in the green arc before taking off, right? Yes, I know Lycoming says only that "[o]il temperature indications should register on the aircraft gage before takeoff is attempted so that problems associated with unusually high oil pressure will be minimized", but allowing it to get up to the green arc really is better for the engine in the long run. Also, as you advance the throttle to full power, if the oil pressure rises to the redline, the oil isn't yet warm enough and you should wait until it warms further.
 
This is an example of what I have been saying about Murphy's Law. It's not that anything that can go wrong will go wrong; it's that most of the time things go right even if they should go wrong and the operator is conditioned to believe they will go right.
Good for you for making yourself check again and see that your RPMs were down and aborting in time.
 
I always waited untill the oil temp. Was in the green before trying takeoff,in my 172,also throttle can get cranky at cold temps.
 
Good call on aborting, if you ever have doubt you already know the answer... As they say in snowboarding hesitation is devastation.

You're waiting till your oil gets to temp (160F or so) before take off right???

Having some, most likely, low time CFI say it's good to go... I wouldn't be happy flying that plane till someone explained to me WHY it did that and what they did to prevent it from occurring again.
 
If it was only spinning to 2000 rpm the lack of acceleration on takeoff should have been a convincing reason to abort.

Oil temp shouldn't have any effect on full power. At least not by the time you did a warm up and run-up. My rule is to see oil temps of 70* before I apply full power. My bigger rule is to see CHTs of 275* before I apply power to taxi. That pretty much assures the oil is warm enough.
 
Yeah, I don't think I'll fly that one for a while.
Thanks for the replies, to answer some of the questions:

The POH says that if the engine is smooth it's ready for takeoff. The temperature wasn't high, I guess I could have waited a little longer, but it shouldn't have been that cold either.
For those with experience on these, how long does it usually take in low 20s to get to a temperature you are comfortable taking off?
Pressure was fine as far as I remember.
Do you think it's possible to only get to 2000 RPM after ten minutes with the engine on because of low temps? (So far I have Ron's vote for no)

The friction lock was not the cause for the hard throttle, I definitely loosened it.

I'm pretty sure the throttle was as far in as it would go, all the way to the stop.

Thanks for the "compliments"on handling the situation. Definitely nothing dangerous or hard to handle, but I did think that if instead of really checking I was just glossing over during takeoff, kind of distracted, it might have been able to get off the ground and into the trees.

By the way, as I was pulling the throttle I felt the mains being a little bouncy, as in trying to leave the ground. I think there might have been half a second or so of flight, so I'm logging this one
 
If your tach is anything like mine, it reads all over the map for the first few minutes on a cold morning. Last week it read zero for a while, then pegged out for a while before stabilizing. I was taught to fly with a partial panel, so my calibrated ear is a good backup.
 
Johann said:
By the way, as I was pulling the throttle I felt the mains being a little bouncy, as in trying to leave the ground. I think there might have been half a second or so of flight, so I'm logging this one
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:lol: The best part of the Happy Hour Landing is currency.

I'm a bit more laid back than some others on here (but still safe) and would have aborted in your situation as well. Good call on that.
 
I have flown airplanes including a fuel injected 172 in very cold conditions. If it's only turning 2000 something is wrong. Unless there was some pilot error like not pushing the throttle in all the way or something I'd be nervous to fly in it again without some problem being noted and addressed.
 
Ron Levy said:
160F before takeoff? What sort of engine would require that? For the Lycoming IO-360 in that 172R, 75F is quite enough.
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I like to see at least 130f, that's on just about everything I've flown, also allows the cylinders time to get to 200F or so.

The "in the green" is a crap mindset IMO.

Watch your oil pressure on t/o.

Check your crankcase breather tube for ice on the preflight, and of course you probably should be running multi weight when it's freezing balls outside.

But hey, nothing flys like a rental ;)

When you own, or rely on the plane for a living it's a little different.
 
It would cook my top end waiting for my oil temp to reach 130* on the ground.

Crankcase breather will almost never be iced on the ground. That happens in flight when it's breathing and the temps are cold. Warm shutdown will clear any ice from the flight.

Just my thoughts.
 
I recall seeing a failing tachometer give inaccurate readings when cold. Could have been that. It's not unusual for analog gauges to malfunction at especially cold temperatures.
 
Stewartb said:
It would cook my top end waiting for my oil temp to reach 130* on the ground.
.
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Really?

I could run my tanks dry without my top end giving me grief on the ground, maybe add some louvers :dunno:
 
Though it seems cold for such a problem, the symptoms -- including Mx finding nothing wrong -- sure sound like intake ice. I suppose a little ice in the fuel manifold might also be problematic.

Obviously not carb ice since there isn't any carb, but it's still possible at least in principle to restrict the intake with ice, as there is still a temperature drop across a partially closed throttle.

When in doubt, abort. The time to decide it was insufficient was right where you did -- on the ground. 100 feet up over the DER might have been a bit of a problem.
 
Brad Z said:
I recall seeing a failing tachometer give inaccurate readings when cold. Could have been that. It's not unusual for analog gauges to malfunction at especially cold temperatures.
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This possible reason seems the most plausible to me, assuming everything else you said is correct (that you pushed the throttle in all the way and the plane was fine later).
 
A mechanical tach is direct drive. Not unusual for one to be 100 rpm off but not 700 off and not intermittently.
 
James331 said:
I like to see at least 130f, that's on just about everything I've flown, also allows the cylinders time to get to 200F or so.
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You'd be waiting a very long time to take off in the winter in most of the USA if you wait for 130F. Where did you come up with that number?

The "in the green" is a crap mindset IMO.
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Well, it meets or exceeds every published recommendation from the FAA, every manufacturer of standard aircraft engines (nontraditional engines like a Rotax notwithstanding), and every engine guru with whom I've ever spoken. Do you have some contrary guidance or recommendation from such a source which you can share with the rest of us?
 
James,

Seriously, I couldn't get my oil anywhere close to 130* on the ground. TCM 520 operating instructions say minimum oil temp for normal ops is 75* if memory serves. And I have louvers. :)
 
Back to the original poster... did it feel sluggish? With three adults in the plane at 2000rpm I'd be surprised if the airplane would leave the ground. Interesting thread!
 
I had a similar experience and it was indeed I didn't have the throttle pushed I'm all the way. I caught it fairly fast and it was a non issue. After that I started moving the seat up more.

I do watch my oil pressure like a mad man though. It's cold out, I have 15w50 in it seems to increase my oil pressure. It's in the green but it's almost to the top of the arc green.
 
cirrusmx said:
did you pay for the time on the botched airplane?
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Nope, I didn't even remember to write down the Hobbs after shutdown with all the unloading passengers and walking back and forth.
They didn't ask and I didn't offer to pay.
They're pretty honest about that, once I had to fly a pattern and go back because I noticed before turning right crosswind that the right wing was leaking fuel like crazy. That one was 0.3 on the Hobbs and they said they were not charging for it (but that one is another story hehe).

Brad Z said:
I recall seeing a failing tachometer give inaccurate readings when cold. Could have been that. It's not unusual for analog gauges to malfunction at especially cold temperatures.
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sixpacker said:
This possible reason seems the most plausible to me, assuming everything else you said is correct (that you pushed the throttle in all the way and the plane was fine later).
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It could be the tach. I was really hoping maintenance would find something. That's the main reason I posted this, to see opinions on what could have caused it since the FBO found nothing. It makes me wonder if I was looking at it wrong, or doing something wrong, but I did two full power run ups after exiting the runway, I can't be that stupid, the needle was not in the green arc, and the throttle was full in.

Stewartb said:
Back to the original poster... did it feel sluggish? With three adults in the plane at 2000rpm I'd be surprised if the airplane would leave the ground. Interesting thread!
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That's a good question, if it was the tach then the plane would have felt normal.
I want to say yes, but:
  • I've never flown with more than one person before (although the weight of these 2 together probably equals my CFI's weight).
  • I'm not used to this plane, I usually fly the 172N.
  • I don't look outside that much until all the inside checks are completed, just enough (and there's a lot of peripheral vision in this) to keep centerline. I mean, I'm glancing outside and inside, not fixating outside, so it's not easy to perceive speed I guess.
  • If I think about it, by the time I aborted I feel that the plane should have been hopping much more trying to get in the air if it was making full power on a day that cold (airport almost at sea level). But because of that time perception shift I mentioned before, maybe it wasn't really that long and that's why it wasn't trying to fly.
I usually enable tracks in Avare so I have a KML, and I was really looking forward to use this to post mortem the issue. Unfortunately I forgot to click on Track Off before shutting down the thing and it looks like all I have is a 0 size KML file :mad2:
 
MAKG1 said:
Though it seems cold for such a problem, the symptoms -- including Mx finding nothing wrong -- sure sound like intake ice. I suppose a little ice in the fuel manifold might also be problematic.

Obviously not carb ice since there isn't any carb, but it's still possible at least in principle to restrict the intake with ice, as there is still a temperature drop across a partially closed throttle.

When in doubt, abort. The time to decide it was insufficient was right where you did -- on the ground. 100 feet up over the DER might have been a bit of a problem.
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I thought about some kind of blockage in the intake, but if it worked fine later then it can only be ice that melted. The day was really clear and the temp/dew point spread was 23 F. Could it still be possible that a previous flight iced it up?
 
did you warm the cabin prior to starting?
 
A couple thoughts:

1) You won't get full RPM on a 172R when at low speeds even when everything is correct, thanks to the fixed-pitch prop. The static RPM range listed on the TCDS for the 172R is from 2065 to 2165. With a mechanical tach, it's hard to take a glance and get a perfect reading - Might it have said 2100, or even 2065? Was it even a sliver above 2000? If so, all may have been perfectly normal.

2) Depending on temp/humidity conditions at the time of flight and during the time leading up to the flight, you may have had ice in the air filter. Did you try alternate air to see if anything changed? If it did, idling ~1200 RPM long enough to heat it up and pull some of that moisture out can help. In really cold weather, I've had times where I couldn't start without carb heat (~= alternate air) because the air filter was iced up.

3) Mechanical tachs aren't always the most accurate instruments in the world. This plus #1 may have meant all was normal. I'm not sure what the allowable tolerance is on a mechanical tach, but I wouldn't be surprised at all if ±100 RPM was allowable, in which case you may have been just fine.
 
Not being familiar with the engine... static should climb rapidly on take off roll, shouldn't it?
 
A couple of years ago I was going out in a C-172M. It was 7°F on the ground. The plane was in the hanger so we didn't bother to pre-heat, and the plane started right up. Everything was normal until I shoved the throttle in to take off. I was just barely getting 1900 rpm. I aborted the takeoff, and taxied back. The mechanic was standing there when I pulled up. He jumps in, tries revving the engine and got almost 2000 rpm. I shutdown, and we pulled the cowl. There was a block of ice under the cowl preventing the throttle from operating properly. To this day we can't figure out how that much water could get in there and freeze in such a manner.
 
flyingcheesehead said:
A couple thoughts:

1) You won't get full RPM on a 172R when at low speeds even when everything is correct, thanks to the fixed-pitch prop. The static RPM range listed on the TCDS for the 172R is from 2065 to 2165. With a mechanical tach, it's hard to take a glance and get a perfect reading - Might it have said 2100, or even 2065? Was it even a sliver above 2000? If so, all may have been perfectly normal.

2) Depending on temp/humidity conditions at the time of flight and during the time leading up to the flight, you may have had ice in the air filter. Did you try alternate air to see if anything changed? If it did, idling ~1200 RPM long enough to heat it up and pull some of that moisture out can help. In really cold weather, I've had times where I couldn't start without carb heat (~= alternate air) because the air filter was iced up.

3) Mechanical tachs aren't always the most accurate instruments in the world. This plus #1 may have meant all was normal. I'm not sure what the allowable tolerance is on a mechanical tach, but I wouldn't be surprised at all if ±100 RPM was allowable, in which case you may have been just fine.
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I have the POH in front of me now, in the Power Check it says:
The engine should run smoothly and turn approximately 2300 - 2400 RPM with mixture leaned to provide maximum RPM
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As for the oil temperature:
During cold weather operations, no indication will be apparent on the oil temperature gage prior to takeoff if outside air temperatures are very cold. After a suitable warm up period (2 to 5 minutes at 1000 RPM), accelerate the engine several times to higher engine RPM. If the engine accelerates smoothly and the oil pressure remains normal and steady, the airplane is ready for takeoff.
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No alternate air switch, but:
The air box has a spring-loaded alternate air door. If the air induction filter should become blocked, suction created by the engine will open the door and draw unfiltered air from inside the lower cowl area. An open alternate air door will result in an approximate 10% power loss at full throttle.
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Johann said:
I was taking two friends up the other day. The plane was a C172R, so fuel injected.
It was pretty cold, I would say low 20s.

When I was past the hold short line I couldn't resist and I held the breaks and gave it full power. Still 2000.
If you look up disappointment in the dictionary, you'll find a picture of my two passenger's faces right there.

I called later and asked, out of curiosity, what they found. They said an instructor took the plane later and found nothing wrong with it.

I did notice that the throttle was a little hard to operate, but as I don't usually fly that plane I'm not sure if this is normal.

Any idea what could have caused this? Maybe too cold and the oil was not hot enough?
.
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You said you don't usually fly that airplane...maybe it has a cruise prop?

I also agree that if the throttle was stiff, that it is very possible that your muscle memory for your right hand and arm told you subconsciously that it was all-the-way-in when indeed it wasn't. It's hard to believe though that you made the same mistake when you did the run-up after you cleared the runway.

When I fly the 172N models, I don't get much more than 2200 RPM on the take-off roll (sea level airport) and it picks up 100 or so more on the climb out as the airplane gains a little more speed.

You did the right thing by aborting. If you get something you have never seen before...it's time to stay on the ground and get it sorted out.

Gene
 
Ether way, 2,000 is way low for a 172, even if its the tach it a fix it before flying again.
 
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