Engine Stutter on Approach

J

JC150

Pre-takeoff checklist
Joined
Apr 22, 2013
Messages
491
Display Name
Display name:
JC150
I was flying a Piper Arrow tonight, and around 2,000' AGL (3,000' MSL) the engine stuttered momentarily. My initial thought was I accidentally brought the mixture to cut off, but it was still running and the vibrations were very pronounced as well.

I was doing about 24" MP/ 2400RPM and 11.5gph with the fuel pump off. It kind of went away on its own after a few seconds, but just in case I moved the fuel flow up to 13gph and reduced the MP to 22" and never had any more issues and continued the approach.

I was just curious if this is an early sign of some kind of stuck valve problem that I should be concerned about? Or did I just have it leaned back too far? I usually keep it somewhat leaned until cleared for the approach, and I've never had any problems flying leaned out around 3,000' MSL.

For context I had just descended from 11,000 feet and the 4 hours of flying leading up to that point was un-eventful. Thanks.
 
Last edited:
Was it still a little lean from the descent?

Possibly a couple drops of water in the gas going through the carburetor.??
 
What engine? I'm thinking it was too lean. BTDT, no tee shirt.
 
Could be the mixture knob, could be a dozen things. Go fly after fueling, set up for the approach similar to how you were yesterday and see if it happens again. Not likely, though. I had a mag give a hiccup a few times (that I ignored over the course of several flights), until the right side finally decided to take a vacation at the most inopportune time.
 
Zeldman said:
Possibly a couple drops of water in the gas going through the carburetor.??
Click to expand...

Arrows all how IO-360's of some flavor. (The turbo arrow has a TSIO-360).

Could have still sucked water but frankly, at 24/24 I'm not sure that's a good explanation. Still, I'd check the strainers and the tanks for any sign of water.
 
Zeldman said:
Was it still a little lean from the descent?

Possibly a couple drops of water in the gas going through the carburetor.??
Click to expand...

I sumped for water at the beginning of the flight and there was no water. You'd think after 4 hours of flying any water would've been at the bottom and would've entered the engine at the beginning of the flight?

It honestly sounded like the engine was quitting for about 3 seconds then everything came back to normal. Afterwards is when I richened the mixture so I'm not sure the mixture was the problem. But I'm really hoping that's all it was and not a stuck valve...
 
JC150 said:
You'd think after 4 hours of flying any water would've been at the bottom and would've entered the engine at the beginning of the flight?
Click to expand...
Perhaps, but I've wondered what happens to the moisture in the air that gets pulled into the tank as you burn gas. 4 hrs in a Piper Arrow up at 11,000 feet would mean the fuel and wings had plenty of time to get nice and cold, maybe as you descended into warmer and more humid air some water condensed out in the tanks and made its way to the engine? Total shot in the dark here, but that's all I could really think of off the top of my head (assuming it is nothing worse)
 
The amount of moisture in the air in tank headspace won't condense to anything appreciable, despite the old wives tail. Twenty gallons of tank headspace at sea level even on a 100% RH 90 day won't contain more than a tenth of an ounce of liquid water.
 
@flyingron interesting, thanks! I figured it wasn't appreciable since I've never had it happen to me, but the thought always lingered in the back of my mind
 
Zeldman said:
Possibly a couple drops of water in the gas going through the carburetor.??
Click to expand...
I've had this happen before. It did shutter for 2 sec or so them cleared up.
flyingron said:
Could have still sucked water but frankly, at 24/24 I'm not sure that's a good explanation. Still, I'd check the strainers and the tanks for any sign of water.
Click to expand...
I would agree after a 4 hour flight it seems unlikely, checking strainers is a good idea.
 
This is where an engine monitor is worth its weight in gold. I had something similar happen on takeoff once. Engine ran rough for a long enough period that I decided to discontinue the flight. Downloaded the flight off the JPI and was able to see that a cylinder went cold. Not likely to be mags so they cleaned the injectors and the lines and nothing ever happened again.
 
The internet does not know :) ask your mechanic.

What the Internet DOES know:
(1) It will not happen again, it was a one time "blip", or
(2) it's going to continue as an intermittent issue, or
(3) it's a precursor to a larger future failure.

I think you know that. I would've gone on here and asked the exact same thing. Pull it out of service and get it looked at if you want real peace of mind. You've got the most to gain or lose out of all of us.
 
JC150 said:
I sumped for water at the beginning of the flight and there was no water. You'd think after 4 hours of flying any water would've been at the bottom and would've entered the engine at the beginning of the flight?

It honestly sounded like the engine was quitting for about 3 seconds then everything came back to normal. Afterwards is when I richened the mixture so I'm not sure the mixture was the problem. But I'm really hoping that's all it was and not a stuck valve...
Click to expand...

Sumping a tank does not guarantee that all the water is out. Water or condensation does not instantly go to the sump. Just a few drops could have held on somewhere in the tank then in the bumpy air it could have worked loose and went through the fuel injection. And in a single engine those few drops can make a couple seconds feel like a couple weeks, just long enough to suck up the upholstery, then clear up as if nothing happened.

And I am not saying this is what happened, it is just a possibility.

I was at FL200 in a C-421 when a little water sucked through in the left engine. At night. Over the Rockies. Man, that woke me up.
 
Your title says "Engine Stutter on Approach" ... any chance you unported a tank momentarily base to final?
 
Zeldman said:
Sumping a tank does not guarantee that all the water is out. Water or condensation does not instantly go to the sump. Just a few drops could have held on somewhere in the tank then in the bumpy air it could have worked loose and went through the fuel injection. And in a single engine those few drops can make a couple seconds feel like a couple weeks, just long enough to suck up the upholstery, then clear up as if nothing happened.

And I am not saying this is what happened, it is just a possibility.

I was at FL200 in a C-421 when a little water sucked through in the left engine. At night. Over the Rockies. Man, that woke me up.
Click to expand...

A few drops of water in a tank have to reach the outlet, which is above the sump by some distance. Then they have to get through the fuel strainer, which has a deep bowl so that water, being heavier, sinks to the bottom and stays there unless we invert the airplane. Then it has to get through the fine-mesh strainer screen, which is really reluctant to pass water when it's wet with fuel. The water's surface tension prevents its passage through such screens. Then it has to get through an even finer screen at the fuel control servo, and if it somehow gets past that, there's another screen at the fuel divider manifold.

Hiccups are far too often blamed on water. Ignition is a bigger problem by nearly an order of magnitude. You should see the insides of magnetos that have been neglected for too many hours or years. Scary.
 
Yep or a bad/fouled plug (mags are really weak-assed things). As someone else pointed out, this is where an engine analyzer is really handy. I had a plug fail and it would manifest itself as short blips in the engine.
 
JAWS said:
http://www.sumpthis.com/
Click to expand...

There's an AD that deals with wrinkles in bladder tanks that trap fuel: 84-10-01R1. That's 37 years ago, and anyone still having water trapped in bladder wrinkles needs to spend more on maintenance. Cessna sells a kit to relocate the drain to pull the wrinkles out, and newer bladders have the drain already relocated to minimize wrinkling.

Furthermore, the fuel strainer will hold better than four ounces of water. That's a lot of water. Judging by the serious corrosion I sometimes find in strainer bowls, some pilots are not draining that strainer before every flight. That's basic airmanship, and one should also be catching the liquid leaving the strainer to see what it is. Don't just let it pee on the ramp; identify it. It might be straight water, which indicates a serious problem somewhere, like a leaky cap letting rainwater in. You might be draining an ounce or two of water onto the ground while leaving just as much still in the strainer. Catch it. Smell it. Feel it. Check its color. This isn't rocket science. If the strainer fills up completely with water, it's more likely that the water will completely stop any further fuel flow through the strainer screen, which is at the top of the strainer bowl, and the engine will quit just as surely as if the water got to the engine. And if the engine just hiccups, it's probably not water at all. It's something else. If there's enough water to get past the screen, that strainer is full of it and that engine is going to get serious indigestion.

When airplanes crash, investigators will carefully check the fuel system for signs of water. They'll check that strainer first thing. If it has plenty of water in it, the cause of failure doesn't remain "unidentified." It's obvious. There are other low spots that can be checked as well, even if the airplane is inverted or shattered into bits. Corrosion could be commonly found in low places in the aluminum tubing, indicating the longtime presence of water, which in turn indicates poor airmanship and maintenance. One of the items on Cessna's inspection sheets is to pull the small plug on the bottom of the fuel selector valve to check for contaminants; it's about the lowest place in the whole system and junk settles there. If I haven't seen the airplane before, I usually find
that plug seized in there tight; never been out since manufacture, and once it's out I get lots of debris and scum and sometimes water. This is not a good sign.

An "unidentified" cause of engine failure usually means carb ice. It leaves no trace, unlike water in fuel.
 
You won't get problems with either bladders or carb ice in an Arrow. As I already pointed out all Arrows have injected (IO-360 variants) engines and they have metal tanks (not to say they might still not retain water). However, if there's no water in the gascolator after landing, that's probably not it either.

I am leaning to Dan's analysis. I'd check the plugs then the mags.
 
Ya definitely not lean as you were rich of peak and peak at that power setting is somewhere in the 9gph range. Air bubble?


Sent from my iPhone using Tapatalk
 
That's exactly what my plane did 5 hours before the left magneto died completely.
 
Maybe your engine has a future in doing uncomfortable interviews with celebrities that are immensely hilarious
 
But how did this amazing quantity of water get into the C-150 tank, unless it was pumped in? The recessed fueling well would protect the fuel from rainwater ingestion assuming any reasonable condition of the fuel cap gaskets. We had a 172M (presumed similar) for 35 years and noted that it was a big deal (like once or twice a year?) whenever any water drops were obtained from the sumps or the gascolator. Bet there was an attorney that did the test.
 
JAWS said:
I couldn't find this on my link above initially. I remember seeing this a few years ago and being astonished.

http://www.sumpthis.com/cessna150andcessna152tanktest/cessna150tanktestimages1024x768.htm
Click to expand...

Couple of things there: I don't remember any 150 I worked on having those depressed fuel outlets. The filler neck is the old recessed type, abandoned by 1970 or so, and I'm thinking that they changed the obviously defective tank bottom geometry at that time, and raised the outlets.

To have the water refuse to go to the sump means that the airplane has to be sitting nose low. The angle of incidence of the wing, plus a properly inflated nosewheel strut, will have the bottom of the tank inclined enough to get the water going where it should.

Newer airplanes are certified under FAR 23. Here's what it says about tanks:

23.971 Fuel tank sump.
(a) Each fuel tank must have a drainable sump with an effective capacity, in the normal ground and flight attitudes, of 0.25 percent of the tank capacity, or 1⁄16 gallon, whichever is greater.

(b) Each fuel tank must allow drainage of any hazardous quantity of water from any part of the tank to its sump with the airplane in the normal ground attitude.

(c) Each reciprocating engine fuel system must have a sediment bowl or chamber that is accessible for drainage; has a capacity of 1 ounce for every 20 gallons of fuel tank capacity; and each fuel tank outlet is located so that, in the normal flight attitude, water will drain from all parts of the tank except the sump to the sediment bowl or chamber.

(d) Each sump, sediment bowl, and sediment chamber drain required by paragraphs (a), (b), and (c) of this section must comply with the drain provisions of §23.999(b)(1) and (b)(2).

That test, done on an improperly nose-low CAR-3 certified airplane, is not indicative of the typical GA airplane out there.
 
nrpetersen said:
But how did this amazing quantity of water get into the C-150 tank, unless it was pumped in? The recessed fueling well would protect the fuel from rainwater ingestion assuming any reasonable condition of the fuel cap gaskets. We had a 172M (presumed similar) for 35 years and noted that it was a big deal (like once or twice a year?) whenever any water drops were obtained from the sumps or the gascolator. Bet there was an attorney that did the test.
Click to expand...

The 172M has raised fuel caps. No recess around the caps. Those recesses were just plain troublesome. The Cessna 180/182/185/188/206/210 had flush fuel caps with recessed latches that would accumulate water that would drain into the tank if the seal around the locking shaft was shot. An AD addessed that, and most were converted to the raised caps. Those that stick with recessed caps have to do an annual/100 hour open-tank inspection to check for water and bladder wrinkles, to check the cap seals, and must have a placard demanding that anytime the airplane gets rained on or is fuelled from a suspect source, the wings gets rocked rather violently with the tail low before each flight to make sure any water gets to the sumps. Such stuff is what drove owners to upgrade the caps, and most also upgraded the wrinkle-prone bladders.

http://www.airweb.faa.gov/Regulator...7CA32CBFD7107A87862569B9004D1566?OpenDocument

Yeah, some attorney might have been involved with that 150 test. If the 150 really was that bad they'd all have crashed by now.
 
I never had a single drop of water in my 150 tanks.
The cap design does change at some point, mine was a 76.
 
mtuomi said:
I never had a single drop of water in my 150 tanks.
The cap design does change at some point, mine was a 76.
Click to expand...
My 76 Skyhawk used to take water in one tank when it would rain. First annual, the mechanic told me they had to be changed... never once have I taken rain with the new caps.
 
I thought it was a pretty good illustration of what can happen inside a small aircraft fuel tank. I always shake the wing and tail during pre-flight before checking the fuel now, even with a Cherokee.
What is that old saying? An ounce of prevention is worth a pound of cure!
 
You must log in or register to reply here.
Back
Top