DA20's engine stopped while taxiing

[polaris]

I got in a DA20 at my flight school yesterday and saw a note that I need to make sure to lean the mixture "a good distance back" during ground operations. I found it strange that it said "three full twists on the mixture," considering that the DA20's mixture lever does not involve turning anything. I suspected it must have been a blanket message to all aircraft in the fleet (most are Cessnas). But since I was not certain, I interpreted the message to mean something along the lines of: "This particular plane has been having problems with inadequate leaning by pilots. Please lean more than you usually would." I thought maybe the mixture lever was mis-calibrated so that I would need to lean farther than I am used to. Anyway, heeding the advice of the note, I made sure to lean pretty far back during my taxi. The engine ran fine, so I decided that it was properly leaned.

But about three minutes later, while I was taxiing to the runway, the engine suddenly stopped. (My girlfriend on board was not pleased.) I figured I must have leaned too far back (try explaining this to your girlfriend) and restarted the engine. It was still unsettling; why did it take so long for the engine to stop? If I had leaned too much, wouldn't I hear the engine sputter as a warning sign before completely seizing? Why would it keep running for three whole minutes and then stop?

After I restarted the engine, I resumed my taxi, but this time I leaned the mixture only about 3/4 inch. I knew leaning 3/4 inch wouldn't do much for ground ops because I know you need to lean pretty far back for it to do much of anything. But whatever. I kept taxiing, but this time, in about 30 seconds, the engine stopped again. At this point, I decided to turn back and call it a day.

When I returned to the flight school, the dispatcher (who is not a pilot) called maintenance. I was asked whether I had the fuel pump on. I am positive I had the fuel pump on during the initial taxi (I remember it; it's on the checklist). But I am not sure if I had it on during my second taxi attempt. I may have inadvertently turned it off in my rush and confusion to restart the engine (I was stalled in the middle of two intersecting taxiways at a busy controlled airport). I am not sure about this.

The fuel pump is REQUIRED during ground ops in the DA20. But I was not aware that if I did not have the fuel pump on, my engine would seize within 30 seconds. I have flown a lot of Pipers before, and they require fuel pump during ground ops. I've accidentally left the fuel pump off during ground ops and the engine did not seize 30 seconds into my taxi.

Do this all seem consistent with my failure to lean the mixture properly and my failure to turn on the fuel pump the second time around?

I am an instrument/commercial with about 300 hours in Cessnas, 200 hours in Pipers, and 50 miscellaneous -- and I have never run into any of these problems before. That is why I am confused and would like some clarification. Thanks in advance.

 

[polaris]

All right, hold up. I am reading the POH for the DA20 and it says MIXTURE FULL RICH during ALL idle power operations. I should not have been leaning AT ALL?

If this is true, the flight school should not have told DA20 pilots to lean at all! I was never told during my DA20 checkout that I should not be leaning at all during ground ops.

 

[MAKG1]

If you could turn the prop by any means afterward, it was not seized.

I have no time in that type, but even in a 172, it can take a while for the engine to respond to a mixture change, especially if it's injected and at low throttle. I had a very similar experience in a new-to-me 172RG that had a somewhat leaner than normal mixture setting.

 

[docmirror]

The fuel pump is REQUIRED during ground ops in the DA20. But I was not aware that if I did not have the fuel pump on, my engine would seize within 30 seconds. I have flown a lot of Pipers before, and they require fuel pump during ground ops. I've accidentally left the fuel pump off during ground ops and the engine did not seize 30 seconds into my taxi.

Your engine didn't seize.

It's a mixture problem. As the engine heats, things change in terms of combustion. Some set of circumstances were in effect that stopped the fuel from being burned. Most likely too lean a mixture, but it could be something else.

I would have done a full power run up and just kept going.

 

[Sac Arrow]

This may be a similar issue to that of DA40's, where due to a tight cowl installation and restricted cooling, the engine runs hot and vapor lock can be a problem on the ground in high temps, particularly at high density altitudes.

 

[docmirror]

All right, hold up. I am reading the POH for the DA20 and it says MIXTURE FULL RICH during ALL idle power operations. I should not have been leaning AT ALL?

If this is true, the flight school should not have told DA20 pilots to lean at all! I was never told during my DA20 checkout that I should not be leaning at all during ground ops.

The flight school is trying to save money by lower fuel use during taxi, and by lowering the engine rebuild times, and other issues by full rich taxi. Learn what these things do, and have someone show you the way to do it right.

 

[Capt. Geoffrey Thorpe]

I would assume you have been asked to lean to reduce lead fouling of the plugs.

The brake torque / speed curve on an engine is very non-linear for piston engines. As you slow down, the friction goes up (at some point quite quickly as bearings fall into different lubrication regimes) and you hit a point where it just quits. You could have been running on the edge and any increase in load due to electrical, wind gust, whatever, could have popped it over the edge.

What kind of engine does it have?

 

[polaris]

I would assume you have been asked to lean to reduce lead fouling of the plugs.

The brake torque / speed curve on an engine is very non-linear for piston engines. As you slow down, the friction goes up (at some point quite quickly as bearings fall into different lubrication regimes) and you hit a point where it just quits. You could have been running on the edge and any increase in load due to electrical, wind gust, whatever, could have popped it over the edge.

What kind of engine does it have?

It has a Continental IO-240-B.

Sorry, "seize" was the wrong word. I should have just said stopped running.

Either way, is it wrong to lean an engine when the POH says to run it full rich all the time? I remember that Cessnas and Pipers have on their POH to "full rich -- lean as necessary." I noticed the DA20 does not say "lean as necessary." Instead, it just says full rich.

 

[jesse]

It has a Continental IO-240-B.

Sorry, "seize" was the wrong word. I should have just said stopped running.

Either way, is it wrong to lean an engine when the POH says to run it full rich all the time? I remember that Cessnas and Pipers have on their POH to "full rich -- lean as necessary." I noticed the DA20 does not say "lean as necessary." Instead, it just says full rich.

You're not going to hurt anything by leaning it as much as possible during idle ground ops. The spark plugs and valves will thank you. Worst case you lean too far and the engine quits.

 

[Henning]

It has a Continental IO-240-B.

Sorry, "seize" was the wrong word. I should have just said stopped running.

Either way, is it wrong to lean an engine when the POH says to run it full rich all the time? I remember that Cessnas and Pipers have on their POH to "full rich -- lean as necessary." I noticed the DA20 does not say "lean as necessary." Instead, it just says full rich.

The reason for leaning is that it reduces plug fouling, you won't hurt anything running as lean as it can run at ground power settings. What you will run into is if at the extreme of lean at idle and you advance the throttle, the engine will stumble or die if you advance a bit too quickly.

 

[docmirror]

It has a Continental IO-240-B.

Sorry, "seize" was the wrong word. I should have just said stopped running.

Either way, is it wrong to lean an engine when the POH says to run it full rich all the time? I remember that Cessnas and Pipers have on their POH to "full rich -- lean as necessary." I noticed the DA20 does not say "lean as necessary." Instead, it just says full rich.

Let me ask you, as I know nothing about the DA planes. Is there anything in there about idle ops or start-up at high altitudes? Does it have a section for leaning when operating above 5000'?

Suppose you went to CO and landed at KCOS, 6187'. You go have lunch, then come back, hop in and start up. Are you going to taxi for 3 miles to the run up area, then take off all while full rich, as the POH says?

 

[polaris]

Let me ask you, as I know nothing about the DA planes. Is there anything in there about idle ops or start-up at high altitudes? Does it have a section for leaning when operating above 5000'?

Suppose you went to CO and landed at KCOS, 6187'. You go have lunch, then come back, hop in and start up. Are you going to taxi for 3 miles to the run up area, then take off all while full rich, as the POH says?

No, I suppose not. The POH has a tiny blurb about operating above 5000' but only when full throttle. "Expect engines to require leaning at full throttle above 5000' pressure altitude."

"At full throttle settings with power less than 75%, it is necessary to lean the engine with the mixture control."

ONLY under cruise: "lean to 25F rich of peak EGT. DO NOT lean by EGT above 75% power."

Nothing under idle ops.

 

[polaris]

Guys, I just got an update from the flight school. Since it was a non-pilot dispatcher informing of this, I could not ask further details. I'll have to call tomorrow and talk to a CFI.

According to the dispatcher, the maintenance person confirmed that the mixture should NEVER be leaned during low-power operations. Period. Something about how, on the DA20, the mixture lever is connected to the fuel primer. Does anyone know anything about this?

 

[docmirror]

Weird. Interesting to find out the fuel system on the DA20. Worries me a bit that you are out there flying it and don't know how it works. For me, a full understanding of the fuel system is a requirement to fly a plane.

 

[Henning]

Guys, I just got an update from the flight school. Since it was a non-pilot dispatcher informing of this, I could not ask further details. I'll have to call tomorrow and talk to a CFI.

According to the dispatcher, the maintenance person confirmed that the mixture should NEVER be leaned during low-power operations. Period. Something about how, on the DA20, the mixture lever is connected to the fuel primer. Does anyone know anything about this?

Why don't you know the systems on the aircraft you are flying? You may want to read this: http://www.tcmlink.com/pdf2/MaintenanceManuals/OI-6/OI-6.pdf

 

[polaris]

There is nothing in the POH that talks about how the mixture works. The section of the fuel system says nothing about the mixture. The extent to which the POH speaks about the mixture:

"When operating at reduced throttle settings, other than steady state cruise, the mixture should always be set to FULL RICH. The only exception to this is operating at very high altitudes." - DA20 POH.

Is it my responsibility to know more about the fuel system than is spelled out in the POH? I am similarly worried that I was not given proper instructions on how to operate this plane. It also worries me that the maintenance department of this flight school put this discrepancy squawk in the plane's logbook without realizing that you are not supposed to lean the engine at low rpm.

Is this my fault for taking at face value what the maintenance department put in the plane's binder, and implementing the recommended procedures? There have been more than one occasion where there were instructions according to this flight school's operation procedures that was DIRECTLY CONTRARY to what was spelled out in the POH. I have asked CFIs about this, and was told "it's a quirk of this plane -- follow the maintenance dpt's recommended procedures."

Is this my fault? Could I/should I have done more here? This really bothers me and if I am inadequately trained, I would like to fix this.

 

[Henning]

It's your responsibility to have all the pertinent information.

 

[polaris]

It's your responsibility to have all the pertinent information.

As in, I should have read, cover to cover, and memorized, the installation and operating manual of the engine of every single plane I fly?

I have asked this question before, and I was told: "No, you are not an A&P mechanic. Know the POH."

 

[docmirror]

There is nothing in the POH that talks about how the mixture works. The section of the fuel system says nothing about the mixture. The extent to which the POH speaks about the mixture:

"When operating at reduced throttle settings, other than steady state cruise, the mixture should always be set to FULL RICH. The only exception to this is operating at very high altitudes." - DA20 POH.

So, back to my questions, there is an exception to full rich for high alt. I kinda thought that would be covered.

As for the fuel system, I haven't flown one, or seen the POH, but there should be a diagram of the fuel system in there. Meh - maybe not.

 

[flhrci]

It's your responsibility to have all the pertinent information.

I would say give the poor guy a break. He did the right thing trying to do what the FBO wanted as well as taking the airplane back because there might have been a problem.

Not every POH has a working theory of the engine. Not every pilot is an A&P or has mechanical knowledge.

The OP did the best he could and made the safe no-go decision and is now just trying to understand what happened.

David

 

[docmirror]

Now looks like the fuel system on the IO-240B may have an altitude compensating fuel pump. That would make sense to leave the mixture alone. The fuel pump should already compensate for barometric changes from alt. I think the mech meant that the mixture was connected to the fuel pump, not fuel primer. If this is the case, then you don't need to lean at alt(for taxi). But, I would confirm this and ask for more clarity.

 

[Henning]

As in, I should have read, cover to cover, and memorized, the installation and operating manual of the engine of every single plane I fly?

I have asked this question before, and I was told: "No, you are not an A&P mechanic. Know the POH."

Whatever, the more you know, the more options you have. The POH doesn't cover everything that can pull your ass out of a bind though, I can tell you that for a fact. Your choice on what kind of a pilot you want to be.

BTW, the FI system on every Continental works the same, goes for the Bendix system on Lycomings as well. Once you know the type, you know the series. All carbs are the same as well outside of the Bendix "pressure carb" which is a throttle body FI system.

 

[polaris]

As for the fuel system, I haven't flown one, or seen the POH, but there should be a diagram of the fuel system in there. Meh - maybe not.

There is a diagram, but it's a piece of crap. It doesn't even show or talk about the mixture levers.

The dilemma I am having is that the maintenance squawks contradict the POH, and I am sometimes told to follow them, and sometimes they turn out to be a mistake by the maintenance dpt. How am I supposed to know? At the end of the day, the POH governs, no matter what an A&P mechanic tells me? That doesn't sound right...

 

[Henning]

There is a diagram, but it's a piece of crap. It doesn't even show or talk about the mixture levers.

The dilemma I am having is that the maintenance squawks contradict the POH, and I am sometimes told to follow them, and sometimes they turn out to be a mistake by the maintenance dpt. How am I supposed to know? At the end of the day, the POH governs, no matter what an A&P mechanic tells me? That doesn't sound right...

You are supposed to know by educating yourself.

 

[docmirror]

Well, as I'm learning, the IO-240B is a bit of a weirdo. The POH trumps all. If you follow that, It's a pretty good bet you can't go wrong. Evidence the don't lean for taxi rule prolly due to the alt compensating pump. It will lean your mixture automatically depending on baro alt.

 

[Henning]

Well, as I'm learning, the IO-240B is a bit of a weirdo. The POH trumps all. If you follow that, It's a pretty good bet you can't go wrong. Evidence the don't lean for taxi rule prolly due to the alt compensating pump. It will lean your mixture automatically depending on baro alt.

Not that much of an oddball, several Continental engines/applications use it, some of the 36 Bonanzas I know had it as well.

 

[polaris]

You are supposed to know by educating yourself.

You are right. I know that not everything is covered by the POH. The more you know, the better. I am going to study the systems more and ask questions when there is any discrepancy, instead of assuming things.

 

[docmirror]

Not that much of an oddball, several Continental engines/applications use it, some of the 36 Bonanzas I know had it as well.

OK, would you say it represents 30% of the engine GA fleet? 20%? 10, 5, 2, 1, .5? I Just see it as an anomaly from the known red knob function from the 19th century forward.

 

[Henning]

You are right. I know that not everything is covered by the POH. The more you know, the better. I am going to study the systems more and ask questions when there is any discrepancy, instead of assuming things.

Here's the best part of the joke when you're flying other people's planes, you fly them the way they want regardless of what you know. "You want me to tear up your gear like that? Ok."

 

[dmspilot]

The altitude compensating system was optional. I've flown a few DA20s and never saw one.

 

[docmirror]

The altitude compensating system was optional. I've flown a few DA20s and never saw one.

Do you recall what the POH said about leaning?

 

[Skylane81E]

Well, as I'm learning, the IO-240B is a bit of a weirdo. The POH trumps all. If you follow that, It's a pretty good bet you can't go wrong. Evidence the don't lean for taxi rule prolly due to the alt compensating pump. It will lean your mixture automatically depending on baro alt.

Even with out the altitude compensating pump they are very easy to over lean and stall on the ground