ECU 'gotcha' in my DA62

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photoSteveZ
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ECU 'gotcha' in my DA62

Post by photoSteveZ »

I was giving some friends their first DA62 experience today in the mountains of Colorado (they're both pilots and own a couple of 'flying' planes and a couple of 'project' planes). When demonstrating the approach and landing I always like to point out the 'speedbrake' effect when pulling the power levers to idle during the flare, due to the ECU programming that flattens the prop blades at low power settings.

We made an overhead crosswind at our first landing field and entered a left downwind to rwy 34. Gear down, flaps 1, 105KIAS. Full flaps and slow to 90-95 over the fence. Imagine my surprise, then, when I arrested the descent, pulled the levers back to the idle stops and...nothing happened. No obvious reduction in power, no increase in prop rpm, no 'speedbrakes'. :scratch:

We floated farther than usual and it took a substantial length of runway and a good deal of braking to slow enough to exit the runway; when I glanced up at the MFD, I was shocked to see that the engines were sitting at 13% power and 1500 rpm. Taxied in, braked to a stop, messed with the power levers a bit more to no avail, and shut down. The props stopped...and feathered. :scratch:

Conditions at KLXV at the time were winds 010@12, altimeter 30.19", OAT 0º C.

Anybody see where this is going?

KLXV is Lake County Airport in Leadville, Colorado, with a field elevation of 9934' MSL; it's the highest paved public airport in the Lower 48 and it's a beautiful place to fly into, particularly since they improved and repaved the runway and ramp in 2019.

A quick exchange of text msgs with my maintenance contacts established that, as altitude increases the ECUs raise the minimum power setting allowed, but no one seemed to know at precisely what altitude that starts.

Well, empirically, I have established that it starts somewhere between 7700' MSL and 9934' MSL, because I have landed at several other high-country airports with elevations in excess of 7500' without encountering this before. After an uneventful takeoff from KLXV we flew south twenty minutes and landed at KANK, elev. 7523' MSL; landing, taxi and shutdown were completely normal.

Live and learn, my old daddy used to say... :shrug: ;)
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Chris
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Re: ECU 'gotcha' in my DA62

Post by Chris »

I was wondering/worrying about this behavior earlier this past week while planning for some trips to Colorado later this year. I don't have any plans to fly into KLXV, but I'm curious how landing at KEIK will feel when DAs are at 9000+ feet in the summertime.
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Re: ECU 'gotcha' in my DA62

Post by Boatguy »

Screen Shot 2021-04-18 at 5.09.43 PM.png
This is from the AE300 Ops manual. At higher altitudes, the ECU's maintain a minimum power to ensure the diesels keep running. I encountered this the first time attempting to descend steeply from 13,000' and couldn't get the power below about 25%. This is for the E4, but your engine will be very close to this chart.
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Rich
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Re: ECU 'gotcha' in my DA62

Post by Rich »

Chris wrote: Mon Apr 19, 2021 12:01 am I was wondering/worrying about this behavior earlier this past week while planning for some trips to Colorado later this year. I don't have any plans to fly into KLXV, but I'm curious how landing at KEIK will feel when DAs are at 9000+ feet in the summertime.
I've got something beyond 10,000 TO/LDGs above 5,000 ft. DA in all sorts of planes. Here's the deal about DA: If not above critical altitude turbo normalized planes may be able to retain climb rate as DA increases but climb angles will be more shallow and takeoff rolls will be longer than at SL. Power is no help with landing distance - they'll also be longer as DA increases.

Your plane will handle it. If I could fly a humble PA28-150 in and out of KEIK in the summer...
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Re: ECU 'gotcha' in my DA62

Post by CFIDave »

I've been waiting for a pilot report from someone landing another Austro-powered Diamond at Leadville KLXV. :D

Years ago while attending Oshkosh I was talking to the chief flight instructor of Embry-Riddle U in Prescott, AZ -- who was describing their pioneering experience of operating some of the first DA42NGs with Austro engines (this was long before ERU bought a bigger fleet of DA42-VI aircraft for their Daytona Beach location.) Since their students asked if they could fly their DA42NGs to Leadville, the chief flight instructor decided it might be a good idea if he tried it first...

He described exactly the same experience Steve had, with the engines unable to throttle back to idle when landing due to the programming of the ECU's to prevent diesel "combustion extinction" at higher altitudes. I guess there aren't any airports in Austria or the Alps at such a high elevation, so the Austro engine programmers may not have considered what happens when you land at nearly 10,000 feet.

Diamond really ought to publish the diagram that Russ (and I) have posted here on DAN in the Diamond AFMs, rather than hiding it away in an Austro Engine manual. More pilots need to be educated about this "unexpected" diesel aircraft engine operation at higher altitudes.
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Re: ECU 'gotcha' in my DA62

Post by CFIDave »

Rich wrote: Mon Apr 19, 2021 12:59 am
Chris wrote: Mon Apr 19, 2021 12:01 am I was wondering/worrying about this behavior earlier this past week while planning for some trips to Colorado later this year. I don't have any plans to fly into KLXV, but I'm curious how landing at KEIK will feel when DAs are at 9000+ feet in the summertime.
I've got something beyond 10,000 TO/LDGs above 5,000 ft. DA in all sorts of planes. Here's the deal about DA: If not above critical altitude turbo normalized planes may be able to retain climb rate as DA increases but climb angles will be more shallow and takeoff rolls will be longer than at SL. Power is no help with landing distance - they'll also be longer as DA increases.

Your plane will handle it. If I could fly a humble PA28-150 in and out of KEIK in the summer...
Rich: this has nothing to do with density altitude. It's caused by the programming of Austro engines so they purposely won't throttle back to idle at higher altitudes to prevent diesel combustion extinction.
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Re: ECU 'gotcha' in my DA62

Post by Rich »

CFIDave wrote: Mon Apr 19, 2021 1:10 am
Rich wrote: Mon Apr 19, 2021 12:59 am
Chris wrote: Mon Apr 19, 2021 12:01 am I was wondering/worrying about this behavior earlier this past week while planning for some trips to Colorado later this year. I don't have any plans to fly into KLXV, but I'm curious how landing at KEIK will feel when DAs are at 9000+ feet in the summertime.
I've got something beyond 10,000 TO/LDGs above 5,000 ft. DA in all sorts of planes. Here's the deal about DA: If not above critical altitude turbo normalized planes may be able to retain climb rate as DA increases but climb angles will be more shallow and takeoff rolls will be longer than at SL. Power is no help with landing distance - they'll also be longer as DA increases.

Your plane will handle it. If I could fly a humble PA28-150 in and out of KEIK in the summer...
Rich: this has nothing to do with density altitude. It's caused by the programming of Austro engines so they purposely won't throttle back to idle at higher altitudes to prevent diesel combustion extinction.
It looks like PA rather than DA is causing this behavior. The Denver area is generally around 5,000 ft elev. but DA can, on really hot days, exceed 8,000, and 7,700 ft. is a standard summer afternoon. Southern WY (and most Colorado) airports are generally <= 7,500 ft elev. It's important to know the distinction. KCOS (elev. 6100) is an example where DA of 9,000 ft. can occur (I've experienced this in said PA28).

And if this effect happens to you you'd better be prepared like us mere mortals. :shock:
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Re: ECU 'gotcha' in my DA62

Post by Chris »

CFIDave wrote: Mon Apr 19, 2021 1:10 am
Rich wrote: Mon Apr 19, 2021 12:59 am
Chris wrote: Mon Apr 19, 2021 12:01 am I was wondering/worrying about this behavior earlier this past week while planning for some trips to Colorado later this year. I don't have any plans to fly into KLXV, but I'm curious how landing at KEIK will feel when DAs are at 9000+ feet in the summertime.
Your plane will handle it. If I could fly a humble PA28-150 in and out of KEIK in the summer...
Rich: this has nothing to do with density altitude. It's caused by the programming of Austro engines so they purposely won't throttle back to idle at higher altitudes to prevent diesel combustion extinction.
Right. I've got enough experience at high DA airports from flying the Lycoming DA40 in Idaho, Wyoming, and Colorado in the summertime, but the idea of not being able to cut power on the DA42 when landing was unsettling. I had incorrectly assumed that higher DA would make the effect worse.

If we take Steve's numbers I think it works out to around 705mb absolute pressure, which from the graph looks like a 20% min power setting. So I guess it's reassuring that he was able to get less than that. Not feeling any need to fly into Leadville, I guess I'll stop worrying about this one for now, although I'll probably go up and play with low power settings at altitude to get a better feel for how it behaves.
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Re: ECU 'gotcha' in my DA62

Post by Steve »

I'm ignorant of the diesel technology, but wouldn't it be possible to have the ECUs turn on the glow plugs at high DA/low power conditions to ensure combustion (this is done with igniters in turbine engines under certain conditions)?
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Re: ECU 'gotcha' in my DA62

Post by photoSteveZ »

Thanks to everyone for chiming in. Except for the surprise factor and the brake pad wear (taxiing at 13% power isn’t fun), there was no safety concern. Takeoff and climb out of LXV was more comfortable by far than it is in my normal-aspirated A36. But in future I won’t land at Leadville in the 62 often, if ever. Too bad, because it really is a stunningly beautiful setting.
IMG_4299 copy.jpg
Last edited by photoSteveZ on Mon Apr 19, 2021 3:21 pm, edited 2 times in total.
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