Engine Failure - Restart Procedures

Keystoner

Keystoner

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Keystoner
I found a great reference by Embry-Riddle Aeronautical University and their Standard Operating Procedures for a Cessna 172.

In their 'Engine Failure During Flight Checklist,' they have two attempts to restart the engine. In the first attempt, the configuration includes Mixture--RICH. If the engine doesn't start, they add a second attempt in which they add Throttle--FULL FORWARD and Mixture--IDLE CUT-OFF. I recognize this is the same as in the procedures for engine fire during start-up but I don't understand it here. The engine can't start with mixture at idle cut-off, right? Pulling the mixture to idle cut-off is exactly how I shut down the engine, so I'm confused.

I have another general question about restart procedures. In the in-plane checklist for the school I attend, in this section, they have, "If prop is stopped, go to start and get it spinning." I want to understand this. Even if I'm in a situation where I'm unable to get the engine started, is it desirable to have the prop spinning anyway?
 
If you flooded engine, the successive cyl. charges will get leaner and leaner until once catches. At that point if it fails to restart, it's not inappropirate mixture.
 
Keystoner said:
I found a great reference by Embry-Riddle Aeronautical University and their Standard Operating Procedures for a Cessna 172.

In their 'Engine Failure During Flight Checklist,' they have two attempts to restart the engine. In the first attempt, the configuration includes Mixture--RICH. If the engine doesn't start, they add a second attempt in which they add Throttle--FULL FORWARD and Mixture--IDLE CUT-OFF. I recognize this is the same as in the procedures for engine fire during start-up but I don't understand it here. The engine can't start with mixture at idle cut-off, right? Pulling the mixture to idle cut-off is exactly how I shut down the engine, so I'm confused.

I have another general question about restart procedures. In the in-plane checklist for the school I attend, in this section, they have, "If prop is stopped, go to start and get it spinning." I want to understand this. Even if I'm in a situation where I'm unable to get the engine started, is it desirable to have the prop spinning anyway?
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The idea behind the second attempt is that you probably flooded the engine with the first attempt, meaning there is way too much fuel in the engine for it to start. Throttle open and mixture cut-off helps purge the excess fuel until it reaches a mixture that will fire. This is actually a common way to start fuel-injected engines, with the mixture at cut-off. Once the engine starts firing and turning, you have several seconds to slowly introduce the mixture again to keep it running.

To your second question. If the engine isn't running, a spinning propeller actually has slightly higher drag than a stopped propeller. However in the restart procedure the point is trying to restart the engine, which kind of requires it be spinning first.
 
midwestpa24 said:
Once the engine starts firing and turning, you have several seconds to slowly introduce the mixture again to keep it running.
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Got it, thanks. I guess it should be intuitive, but if I'm writing that checklist, I'd add the part about enrichening the mixture if the engine sounds like it's ready to turn over.

midwestpa24 said:
To your second question. If the engine isn't running, a spinning propeller actually has slightly higher drag than a stopped propeller. However in the restart procedure the point is trying to restart the engine, which kind of requires it be spinning first.
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So the answer to my question is 'no.' If I can't get it started, I'll take the decreased drag of the stopped prop to maximize my glide if necessary.
 
Flooding an engine in flight would require either a stuck carb float, or some really poor engine management. Full rich at altitude on a hot day could do it. Leaving the primer unlocked could do it, especially on approach or in a low-power descent where the low MP is sucking hard on it. Even with the stuck carb float, the mixture could be leaned to keep it running until it's on the ground.

This old technology requires some knowledge of how things work. Doing stuff by rote is a poor way to try to fix it. Carb ice, for instance is VERY poorly understood by many pilots, some of whom think it's a cold-weather-only thing. Training for carb ice is difficult, too, since it's impossible to simulate it. It takes reading and thinking and understanding a few basic laws of physics and, for some, that's too much work.

51nVYVeaDGL._SX382_BO1,204,203,200_.jpg


Buy it and study it.
 
Keystoner said:
Got it, thanks. I guess it should be intuitive, but if I'm writing that checklist, I'd add the part about enrichening the mixture if the engine sounds like it's ready to turn over.
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I'm such an idiot. They have it, plain as day, I just needed to keep reading. They provide an explanation of each item of the checklist following the checklist. They included this note:
If the engine starts, depress the Mixture Control knob and smoothly move the Mixture Control to the Full Forward (Full Rich) position, and adjust the throttle to set the desired power setting. ​
 
Dan Thomas said:
Flooding an engine in flight would require either a stuck carb float, or some really poor engine management. Full rich at altitude on a hot day could do it. Leaving the primer unlocked could do it, especially on approach or in a low-power descent where the low MP is sucking hard on it. Even with the stuck carb float, the mixture could be leaned to keep it running until it's on the ground.
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Please realize newer 172s don't have a carb, which is the type I'm assuming this flight school is using. And the fuel injected Lycomings they do use can flood rather easily if they aren't firing. My alma mater flight school had issues. That is why the second method of attempting to restart the engine was added. My flight school put a 6 month old 172 into a field after an engine failure and failed restart. The engine failed during power off stalls, due to an incorrect idle mixture setting. The restart failed because they attempted the traditional full rich, fuel pump on procedure which just dumped fuel into the engine.
 
Keep in mind that ER is in Florida. Not only is the ambient temperature high most of the year, but the planes are often flown back-to-back (at ER there are often two students per plane & they land & switch seats mid-lesson) so the engines are hot. Vapor lock is always a concern.

If you have the time & altitude to attempt an in-flight restart, you either have to spend attention cranking the starter or just bump the starter to get the prop windmilling and then focus on something else. Obviously, getting a stopped prop to start windmilling by cranking the starter means you have more time to fiddle with fuel, carb heat, mixture, & mags. Oh…and fly the plane.
 
midwestpa24 said:
Please realize newer 172s don't have a carb, which is the type I'm assuming this flight school is using.
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Oh, yes, of course. Embry won't have carbs or primers. But the rest of the engine management stuff will apply.
 
Keystoner said:
I recognize this is the same as in the procedures for engine fire during start-up but I don't understand it here. The engine can't start with mixture at idle cut-off, right? Pulling the mixture to idle cut-off is exactly how I shut down the engine, so I'm confused.
Click to expand...

The person at ER who wrote the procedure is an idiot. I recommend you read the procedure in the Cessna 172 AFM/POH.
 
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rhkennerly said:
Keep in mind that ER is in Florida. Not only is the ambient temperature high most of the year, but the planes are often flown back-to-back (at ER there are often two students per plane & they land & switch seats mid-lesson) so the engines are hot. Vapor lock is always a concern.

If you have the time & altitude to attempt an in-flight restart, you either have to spend attention cranking the starter or just bump the starter to get the prop windmilling and then focus on something else. Obviously, getting a stopped prop to start windmilling by cranking the starter means you have more time to fiddle with fuel, carb heat, mixture, & mags. Oh…and fly the plane.
Click to expand...

Vapor lock example:
https://www.reddit.com/r/flying/comments/scxjfv/other_video_got_deleted_but_heres_another_angle/
 
You can get an engine kick over at idle cut-off. It just won't run very long. Sometimes it will run longer than you think should be possible. Seen that on the ground which is why I'll always treat a prop like it could start at any time.
 
dmspilot said:
If the prop is stopped the engine is guaranteed not to start.
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Anyone else ever "air-started" a piston engine (prop stopped)? No starter, just altitude and patience. And surprisingly, it really doesn't take as much altitude as one might think.

I wouldn't recommend it as an emergency procedure. But, it is possible.
 
wilkersk said:
Anyone else ever "air-started" a piston engine (prop stopped)? No starter, just altitude and patience. And surprisingly, it really doesn't take as much altitude as one might think.

I wouldn't recommend it as an emergency procedure. But, it is possible.
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Tried it once in 150. Pulled the mix, slowed the airplane until the prop stopped just before the stall, and then glided a bit before diving to see when it would kick over. Got to Vne first. Had to bump the starter. A stopped prop is totally stalled, inverted, near 90° AoA, and has little torque applied to it in that condition. As long as it's turning it's negative AoA is much less and the wind will drive it.
 
Dan Thomas said:
Tried it once in 150. Pulled the mix, slowed the airplane until the prop stopped just before the stall, and then glided a bit before diving to see when it would kick over. Got to Vne first. Had to bump the starter. A stopped prop is totally stalled, inverted, near 90° AoA, and has little torque applied to it in that condition. As long as it's turning it's negative AoA is much less and the wind will drive it.
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Huh! I haven't tried it in a 150. But, my little airplane has a Sterba 52/42 wood prop on a 60hp VW conversion. Twice now, I've goofed up an aerobatic manuever and inadvertently achieved negative G (not conducive for fuel flow in carbureted engines). Both times with plenty of altitude and somewhere to go if it didn't all work out, I've continued to straight down and in a vertical dive, the engine restarted right at 130mph. After a 3.5 G pull out, this only took about 2,000' of altitude to accomplish.
 
Dan Thomas said:
This old technology requires some knowledge of how things work. Doing stuff by rote is a poor way to try to fix it. Carb ice, for instance is VERY poorly understood by many pilots, some of whom think it's a cold-weather-only thing. Training for carb ice is difficult, too, since it's impossible to simulate it. It takes reading and thinking and understanding a few basic laws of physics and, for some, that's too much work.
Click to expand...
yup! This is my biggest issue with a lot of today's pilot culture and instruction. It's remarkably rote. Checklists and procedures are important, but one must always understand the logic behind these things.. but that requires a lot of work from both the instructor and the student, and for many it's just easier to lean on a checklist and rote memory
 
Dan Thomas said:
Oh, yes, of course. Embry won't have carbs or primers. But the rest of the engine management stuff will apply.
Click to expand...

The nickname for Embry-Riddle is Riddle, not Embry. ERAU '91 Daytona
Everyone have a great day.
 
Other than flooded condition from the boast pump in the prime position, I trying to figure out what a lean start would accomplish.
 
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