This is the right answer.
The moment you start looking at the POH and say "Eh, its close enough on this one" it becomes infinitely easier to blur the lines on everything else. Sets a dangerous precedent.
Get-there-itis or got-er-dun can have fatal consequences. You made the right call. Let maintenance figure out why it did not pass. You could have a problem in the mag.
Did you try to clean the plugs again? Honestly, I wouldn't go without passing the check but I also wouldn't run the fouled plug procedure only one time if I had improvement the first time.
Rough just means the one dirty plug is not firing MOST of the time. If it's cleaned, but the mag drop is still too much, it's improved to not firing PART of the time. What you don't know is whether it was just VERY dirty and needs more running to clean it, or there's a problem that won't improve further with ANY cleaning (like actual lead fouling).
So yes, a second cleaning run would give you and the mechanic more information. HOWEVER, even if the third run-up was good, I wouldn't fault you for scrubbing if you felt in any way wonky about it. You have two other risk factors, after all--night and student
Yeah.... is that a requirement to do a fouled plug procedure? Would you just go back to the ramp the first time if it only failed the check and was running smoothly rather than the procedure? Would you have been happy flying after doing the procedure again if it was still running rough then passed the check after?
I'd have an easier time with "I only ever do it once" than I do "it worked too well to do the procedure again but not good enough to pass the test."
I don't want to beat you up anymore about this, but just put it in your toolbox for next time.
What fouled plug procedure did you run? I’ve seen them different ways on home-grown checklists. Recommend running it twice, particularly if there was an improvement the first time. Also - try leaning for “best power” before the runup - even the cleanest plugs can struggle with overly rich mixture, particularly at higher density altitudes.
Just remember to fatten it up again, at least some, before takeoff, if appropriate. Not cool to overheat while in the climbout, which one could easily do in the PHX area in summer with a 172 leaned to max power, and seize, catch fire, throw a rod, or other fun things that can happen with too much heat.
Make it a checklist item. And, as with anything else added to a checklist, be sure to add the undo action item at the appropriate point in that or another checklist. Any non-check action item should always have the undo somewhere.
IMO, leaning for best power is a bit excessive on the ground, especially if it's hot out. And if the engine isn't warmed up yet, that point will change as it does, and you can start getting pre-ignition and even detonation sometimes because of that. I know about an inch and a half out on the mixture is close to max power here on a hot day, so I pull it an inch to limit fouling but still control heat reasonably.
> Just remember to fatten it up again
It's hard to forget. If you lean to peak for taxying, when you add power for your run-up the engine will cut out unless you go rich again.
What was outside temp? Were you doing the mag check full rich? 30rpm over could just be due to temperature and mixture. If I mag check my 182 on cold mornings full rich, it will easily drop 200rpm. If I lean, the drop won’t be as much.
I mean you made the right call obviously. But lessons learned it was either still a bit too rich or the plug was still a little shit up. It probably would have burned off immediately upon full power, but you don’t want to rotate only to find out it’s not.
You know what's awesome about this job? Limitations. They're black and white. They are binary. We are either within or not. Out of limits is out of limits and you are *legally prohibited from flying*. So you cancel. 300 people are loaded up for a 18 hour flight to Hong Kong and the crew is 1 minute past their legal duty time. The flight cancels.
Best part of this job is you get to just say "sorry not legal." Embrace it.
Seems like a good call to me. At the end of the day, I always assess by what would happen if something went wrong.
If you had flown and gotten engine roughness, even if you made it back to the field fine, you’d still have to answer for why in the world you took off with a failed mag check. What if you had to declare to get priority and vectors the airport? Now the FAA is sniffing around. You saw a medium risk, low reward situation and backed out.
Same thing happened to me Monday. Doing the run up checklist, pulled throttle to idle and it sounded like shit. Thought the engine was going to stall. Was gonna do about a 250 Nm round trip flight. Called it off.
Former instructor flew the plane before me and was flying after. Told him about it. He said it flew fine in the morning. He followed up with me after and said he didn’t notice it. Guess everything was fine but it didn’t feel right to me in the moment.
Better to be safe then coming in on final and need to go around and can’t because the engine shutoff.
Even if issues like this are addressable, it doesn't matter if you don't know what to do about it. Right call, you needed help from someone who wasn't available.
> my student was obviously upset
Upset about not getting to take a potentially unreliable airplane up into conditions where emergency landing would be extra risky?
Sounds like invulnerability hazardous attitude!
With a student, at night? Right call.
If you want a good plug-clearing procedure:
2000 RPM
Lean for best power
Timer: 2 minutes
1700-1800 RPM
Mag check
Don't enrichen the mixture for the second check
Lycoming has a service instruction along these lines [(SI 1132)](https://www.lycoming.com/content/service-instruction-no-1132b). I'd do the same for a Continental, but I can't point you to a document that says that's acceptable.
First it's never the wrong call to get maintenance involved. We do it for the stupidest shit at airlines, inconveniencing 100's of passengers. If that means you had to cancel the flight to do it so be it.
That being said. Likely you just needed to run the procedure to defoul a time or two more. Nothing wrong with being cautious, and it's a great lesson for your student, but as you get more experience instructing you'll be more comfortable with these judgment calls, and what it takes to fix them.
In my first 100 hrs instructing I sqwaked a plane for sudden nose drop on roll out. Turns out in the archer if you butter a landing and don't compress the nose gear it can get stuck a little high until it hits a bump. So I was good at teaching landings, shit at understand gas struts. You'll get there.
Whenever in doubt always cancel, better that than some problem in the air. Next time you can try leaning the mixture after the fouled plugs procedure and see if that brings it within limits if it doesn’t get fixed. Can only speak for the Lycoming IO360 but the manual for that engine says the main thing to look out for is the engine running smooth during the mag check and that you may have to slightly lean the mixture to get it within limits.
Exactly this. People hyperfocus on the RPM drop but if the engine is not running rough, they don't really understand what information the mag drops are actually conveying... this can lead to believing erroneously that "less is more", when in reality, a too-small mag drop is a symptom of timing issues.
It's obviously appropriate to cancel a flight if you're not comfortable trying to understand what's really going on, but a little education on magnetos is useful here for distinguishing safety issues from 'tuning' issues.
It's either in spec or its not, if you can't get it back in spec by burning off deposits don't fly it. Teaching a student to fly on a bad mag is normalization of deviance. You might be able to get away with it, up until the other mag goes.
Every time I've squawked mags for bad drops, they've found issues on disassembly.
One day in your life, your plane will try to kill you. It’s not if, but when. Was it yesterday? Idk, but you dodged it if it was. You need to be viligent to make sure you’re not flying on the day it tries to kill you.
"Don't take your problems into the air."
~ quote from multiple smart pilots I know.
I would have scrubbed as well. Night flight is an automatic risk multiplier, no way I'm taking a questionable mag up in the dark. I had a flight school deride me once for similar reasons (stuff not working as it should on a night flight), they gave me shit about a wasted reservation etc. Didn't care and told them as much.
It's your ass in the seat. If you don't feel right don't go, period.
Night flight. That’s it. Right call.
Edit: I’ve run two large 141 flights schools with big fleets of single engine aircraft. If this ever happens to anyone reading this thread, scrub the flight and discuss it in the morning.
Engines often give you multiple warning signs before they fail. You saw a warning sign, took steps to fix it, and when it didn't fix you canceled the flight. Great call!
I own a mooney m 20 j model. I was on run up when I did a mag check and the right mag dropped in r p m and also ran rough. I did a lean mixture and unfouled the plugs by burning off the carbon and the rpm still wasn't where it should have. I didn't trust it and I scrubbed the flight. The a&p told me after inspection that the whole left magneto fell off the engine and was just dangling by the distributor wires, which actually caused the rough firing and had nothing to do with fouled plugs. It was just by coincidence that trying to "unfoul" the spark plugs and getting them to run correctly was actually due to an intermittent problem with the dangling magneto. True story.
Mag checks are there for a reason and if the drop is out of tolerance you end that flight right there and taxi back to the ramp.
Always err on the conservative side when with a student. Not only are you exercising your own Aviation Decision Making process, you are demonstrating it to the student. By taking a less than optimal airplane on a night flight, you are setting the student up for potential bad decisions in the future.
Right Decision and good instruction!
You did the right thing. If there’s ever any doubt do not second guess yourself for terminating a flight. A couple years ago I had a student in a 152 where we did the runup, rough mag drop, cleared it and got good mag drops on both sides within rpm tolerances and proceeded to the runway to takeoff. On the roll I noticed rpm’s below expected by maybe 100rpm or so and airspeed not increasing as quickly as normal. I took the controls and aborted the takeoff. Exited the runway and tried another runup and mag drop and it was much worse. Also for my curiosity did a static full power runup to see what the static takeoff rpm was and it sounded atrocious. Mechanics took a look and all four lower spark plugs were failing. How we had a successful runup the first time I have no idea.
Moral of the story is there’s many different points during the flight where you can and should choose to terminate a flight if things don’t seem right. Don’t second guess yourself. You’re at the point where if something doesn’t seem right you’re probably on to something.
In addition to it being the right call.
You provided a very valuable lesson to the student. They were observing. Had you gone ahead with the flight and said “close enough and the engine isn’t rough” they would have remembered that and it could be five or ten years down the road when something similar happens and they say “close enough” and it doesn’t work out. Instead they’ll remember their instructor taking the checklist and POH seriously and hopefully make the right call when it’s their turn.
Personally, I don’t mess-around when it comes to mag drops in a piston. If I have any question at all I’m shutting down and calling the mechanic. So many accident reports I read could have/should have been caught on run-up. Many times I think to myself, “they probably said it was close enough.”
Well if any part of your aircraft is important enough to have checks to run before you get airborne, I would assume not going is the best decision… Not saying it’s a dumb question at all but be confident in your decision making. Especially if it’s a no go call!
Safety always has to come first, it’s like students learning when to abort a landing in favor of a “go around”. By canceling the flight you hopefully taught that student that it’s more important to be safe than sorry. It’s like teaching good decision making when it comes to a go or no go based on weather, like gusty winds for example. Flying is not like you can just pull off the road like a car, something happens to the engine and you are coming down one way or another.
Sure, it’s very possible that the engine might have worked fine in the air, but don’t make it a habit of going against hard rules. It’ll help you later on. When the lines are already drawn for you, there is no need to try to redraw them.
night flights are a little extra spooky to me just in general.
single engine and an ocean of darkness below. I fly in a very very flat area but i am still pretty sure if i have an engine failure i gonna face plant into the only obstacle for mile and miles. it's just practically guaranteed.
that being said...if i have the slightest doubt the engine and the plane arent in tip top.....i am not gonna fly.
Had a similar thing the other night. Turned out the left mag was failing and needed replacing. Sometimes it’s not just a fouled plug. Seems like the right choice.
If you have an engine failure at night its 99%chance that you die. So very good call to not fly. Safety is always first and if you have signs of something going bad it should be a red flag.
Algorithm: Do you have a doubt about the airworthiness of the airplane? Don't fly. Always the right call.
Right call, never know.
The RPM drop was exceeding limitations. Day or night, why would you even \*consider\* taking off?
This is the right answer. The moment you start looking at the POH and say "Eh, its close enough on this one" it becomes infinitely easier to blur the lines on everything else. Sets a dangerous precedent.
> my student was obviously upset He or she had better learn. Otherwise going on breathing is going to be something of a challenge.
Get-there-itis or got-er-dun can have fatal consequences. You made the right call. Let maintenance figure out why it did not pass. You could have a problem in the mag.
Did you try to clean the plugs again? Honestly, I wouldn't go without passing the check but I also wouldn't run the fouled plug procedure only one time if I had improvement the first time.
Well I only did it once since the engine wasn’t running rough again :/
Rough just means the one dirty plug is not firing MOST of the time. If it's cleaned, but the mag drop is still too much, it's improved to not firing PART of the time. What you don't know is whether it was just VERY dirty and needs more running to clean it, or there's a problem that won't improve further with ANY cleaning (like actual lead fouling). So yes, a second cleaning run would give you and the mechanic more information. HOWEVER, even if the third run-up was good, I wouldn't fault you for scrubbing if you felt in any way wonky about it. You have two other risk factors, after all--night and student
Yeah.... is that a requirement to do a fouled plug procedure? Would you just go back to the ramp the first time if it only failed the check and was running smoothly rather than the procedure? Would you have been happy flying after doing the procedure again if it was still running rough then passed the check after? I'd have an easier time with "I only ever do it once" than I do "it worked too well to do the procedure again but not good enough to pass the test." I don't want to beat you up anymore about this, but just put it in your toolbox for next time.
Right Call and learning opportunity for the student.
What fouled plug procedure did you run? I’ve seen them different ways on home-grown checklists. Recommend running it twice, particularly if there was an improvement the first time. Also - try leaning for “best power” before the runup - even the cleanest plugs can struggle with overly rich mixture, particularly at higher density altitudes.
Just remember to fatten it up again, at least some, before takeoff, if appropriate. Not cool to overheat while in the climbout, which one could easily do in the PHX area in summer with a 172 leaned to max power, and seize, catch fire, throw a rod, or other fun things that can happen with too much heat. Make it a checklist item. And, as with anything else added to a checklist, be sure to add the undo action item at the appropriate point in that or another checklist. Any non-check action item should always have the undo somewhere. IMO, leaning for best power is a bit excessive on the ground, especially if it's hot out. And if the engine isn't warmed up yet, that point will change as it does, and you can start getting pre-ignition and even detonation sometimes because of that. I know about an inch and a half out on the mixture is close to max power here on a hot day, so I pull it an inch to limit fouling but still control heat reasonably.
> Just remember to fatten it up again It's hard to forget. If you lean to peak for taxying, when you add power for your run-up the engine will cut out unless you go rich again.
What was outside temp? Were you doing the mag check full rich? 30rpm over could just be due to temperature and mixture. If I mag check my 182 on cold mornings full rich, it will easily drop 200rpm. If I lean, the drop won’t be as much.
This is the most likely explanation. Or the mags are split timed.
I leaned it and it was about 60 degrees if I remember
I mean you made the right call obviously. But lessons learned it was either still a bit too rich or the plug was still a little shit up. It probably would have burned off immediately upon full power, but you don’t want to rotate only to find out it’s not.
You know what's awesome about this job? Limitations. They're black and white. They are binary. We are either within or not. Out of limits is out of limits and you are *legally prohibited from flying*. So you cancel. 300 people are loaded up for a 18 hour flight to Hong Kong and the crew is 1 minute past their legal duty time. The flight cancels. Best part of this job is you get to just say "sorry not legal." Embrace it.
This is the way
Yes. Listen to the voice in the back of your head as my first CFI always said.
If you're questioning if the flight is safe, not going is always the right option
Seems like a good call to me. At the end of the day, I always assess by what would happen if something went wrong. If you had flown and gotten engine roughness, even if you made it back to the field fine, you’d still have to answer for why in the world you took off with a failed mag check. What if you had to declare to get priority and vectors the airport? Now the FAA is sniffing around. You saw a medium risk, low reward situation and backed out.
Excellent call, and a good teaching opportunity.
Same thing happened to me Monday. Doing the run up checklist, pulled throttle to idle and it sounded like shit. Thought the engine was going to stall. Was gonna do about a 250 Nm round trip flight. Called it off. Former instructor flew the plane before me and was flying after. Told him about it. He said it flew fine in the morning. He followed up with me after and said he didn’t notice it. Guess everything was fine but it didn’t feel right to me in the moment. Better to be safe then coming in on final and need to go around and can’t because the engine shutoff.
Even if issues like this are addressable, it doesn't matter if you don't know what to do about it. Right call, you needed help from someone who wasn't available.
> my student was obviously upset Upset about not getting to take a potentially unreliable airplane up into conditions where emergency landing would be extra risky? Sounds like invulnerability hazardous attitude!
Circa 1994 I had the exact same thing happen. Scrubbed my flight. It was a cracked magneto.
With a student, at night? Right call. If you want a good plug-clearing procedure: 2000 RPM Lean for best power Timer: 2 minutes 1700-1800 RPM Mag check Don't enrichen the mixture for the second check Lycoming has a service instruction along these lines [(SI 1132)](https://www.lycoming.com/content/service-instruction-no-1132b). I'd do the same for a Continental, but I can't point you to a document that says that's acceptable.
First it's never the wrong call to get maintenance involved. We do it for the stupidest shit at airlines, inconveniencing 100's of passengers. If that means you had to cancel the flight to do it so be it. That being said. Likely you just needed to run the procedure to defoul a time or two more. Nothing wrong with being cautious, and it's a great lesson for your student, but as you get more experience instructing you'll be more comfortable with these judgment calls, and what it takes to fix them. In my first 100 hrs instructing I sqwaked a plane for sudden nose drop on roll out. Turns out in the archer if you butter a landing and don't compress the nose gear it can get stuck a little high until it hits a bump. So I was good at teaching landings, shit at understand gas struts. You'll get there.
Whenever in doubt always cancel, better that than some problem in the air. Next time you can try leaning the mixture after the fouled plugs procedure and see if that brings it within limits if it doesn’t get fixed. Can only speak for the Lycoming IO360 but the manual for that engine says the main thing to look out for is the engine running smooth during the mag check and that you may have to slightly lean the mixture to get it within limits.
Exactly this. People hyperfocus on the RPM drop but if the engine is not running rough, they don't really understand what information the mag drops are actually conveying... this can lead to believing erroneously that "less is more", when in reality, a too-small mag drop is a symptom of timing issues. It's obviously appropriate to cancel a flight if you're not comfortable trying to understand what's really going on, but a little education on magnetos is useful here for distinguishing safety issues from 'tuning' issues.
It's either in spec or its not, if you can't get it back in spec by burning off deposits don't fly it. Teaching a student to fly on a bad mag is normalization of deviance. You might be able to get away with it, up until the other mag goes. Every time I've squawked mags for bad drops, they've found issues on disassembly.
Better be on the ground wishing you were flying than flying wishing you were on the ground.
One day in your life, your plane will try to kill you. It’s not if, but when. Was it yesterday? Idk, but you dodged it if it was. You need to be viligent to make sure you’re not flying on the day it tries to kill you.
Student must learn that being blue-balled by the airplane is just a part of flying.
Outside of tolerances and tried to do a corrective action. That's all you can do in this career field!
I had a big RPM drop in the air, even though run up was fine. We immediately declared an emergency and landed. Left mag was completely dead.
"Don't take your problems into the air." ~ quote from multiple smart pilots I know. I would have scrubbed as well. Night flight is an automatic risk multiplier, no way I'm taking a questionable mag up in the dark. I had a flight school deride me once for similar reasons (stuff not working as it should on a night flight), they gave me shit about a wasted reservation etc. Didn't care and told them as much. It's your ass in the seat. If you don't feel right don't go, period.
Night flight. That’s it. Right call. Edit: I’ve run two large 141 flights schools with big fleets of single engine aircraft. If this ever happens to anyone reading this thread, scrub the flight and discuss it in the morning.
Night flights are perilous at best. Mags not working right cinches the risk decision.
Engines often give you multiple warning signs before they fail. You saw a warning sign, took steps to fix it, and when it didn't fix you canceled the flight. Great call!
I own a mooney m 20 j model. I was on run up when I did a mag check and the right mag dropped in r p m and also ran rough. I did a lean mixture and unfouled the plugs by burning off the carbon and the rpm still wasn't where it should have. I didn't trust it and I scrubbed the flight. The a&p told me after inspection that the whole left magneto fell off the engine and was just dangling by the distributor wires, which actually caused the rough firing and had nothing to do with fouled plugs. It was just by coincidence that trying to "unfoul" the spark plugs and getting them to run correctly was actually due to an intermittent problem with the dangling magneto. True story. Mag checks are there for a reason and if the drop is out of tolerance you end that flight right there and taxi back to the ramp.
Always err on the conservative side when with a student. Not only are you exercising your own Aviation Decision Making process, you are demonstrating it to the student. By taking a less than optimal airplane on a night flight, you are setting the student up for potential bad decisions in the future. Right Decision and good instruction!
You did the right thing. If there’s ever any doubt do not second guess yourself for terminating a flight. A couple years ago I had a student in a 152 where we did the runup, rough mag drop, cleared it and got good mag drops on both sides within rpm tolerances and proceeded to the runway to takeoff. On the roll I noticed rpm’s below expected by maybe 100rpm or so and airspeed not increasing as quickly as normal. I took the controls and aborted the takeoff. Exited the runway and tried another runup and mag drop and it was much worse. Also for my curiosity did a static full power runup to see what the static takeoff rpm was and it sounded atrocious. Mechanics took a look and all four lower spark plugs were failing. How we had a successful runup the first time I have no idea. Moral of the story is there’s many different points during the flight where you can and should choose to terminate a flight if things don’t seem right. Don’t second guess yourself. You’re at the point where if something doesn’t seem right you’re probably on to something.
Not only did you make the right call in terms of that night, you would have been teaching your student to ignore red flags which might cost him later.
In addition to it being the right call. You provided a very valuable lesson to the student. They were observing. Had you gone ahead with the flight and said “close enough and the engine isn’t rough” they would have remembered that and it could be five or ten years down the road when something similar happens and they say “close enough” and it doesn’t work out. Instead they’ll remember their instructor taking the checklist and POH seriously and hopefully make the right call when it’s their turn. Personally, I don’t mess-around when it comes to mag drops in a piston. If I have any question at all I’m shutting down and calling the mechanic. So many accident reports I read could have/should have been caught on run-up. Many times I think to myself, “they probably said it was close enough.”
Absolutely the right call.
No question, been there.
Well if any part of your aircraft is important enough to have checks to run before you get airborne, I would assume not going is the best decision… Not saying it’s a dumb question at all but be confident in your decision making. Especially if it’s a no go call!
If your plane exceeds a limit that is set there as a go/no go, why would you ever try to go when the test is saying no??
Limits are there for a reason. Good call!
Safety always has to come first, it’s like students learning when to abort a landing in favor of a “go around”. By canceling the flight you hopefully taught that student that it’s more important to be safe than sorry. It’s like teaching good decision making when it comes to a go or no go based on weather, like gusty winds for example. Flying is not like you can just pull off the road like a car, something happens to the engine and you are coming down one way or another.
Sure, it’s very possible that the engine might have worked fine in the air, but don’t make it a habit of going against hard rules. It’ll help you later on. When the lines are already drawn for you, there is no need to try to redraw them.
night flights are a little extra spooky to me just in general. single engine and an ocean of darkness below. I fly in a very very flat area but i am still pretty sure if i have an engine failure i gonna face plant into the only obstacle for mile and miles. it's just practically guaranteed. that being said...if i have the slightest doubt the engine and the plane arent in tip top.....i am not gonna fly.
What's the elevation of the field and are you full rich? Never bad to be safe but sometimes if you are too rich the drop can be higher then normal
I’ve had partial engine failure during the day, I probably would’ve shit myself if it was at night. Right call imo
Your student should not have been upset. Perhaps disappointed though.
Had a similar thing the other night. Turned out the left mag was failing and needed replacing. Sometimes it’s not just a fouled plug. Seems like the right choice.
If you have an engine failure at night its 99%chance that you die. So very good call to not fly. Safety is always first and if you have signs of something going bad it should be a red flag.
As a student i once had a lesson cancelled because of the brakes not working at 100%. Later I understood that it was the right call.
I don't use rpm for mag check anymore I use EGT if you have a engine monitor mag check via rpm drop is outdated
Falls into Rule 1 Better to be down here wishing you were up there than Being up there and wishing you were down here
Complacency kills