Rotax Turbo

[podpilot]

Tecnam Astore 2015, ~150 hours, Rotax 914 turbo. Flown 20 hours since annual in March Without any issues. Flying today, July 16, 2018; Engine stopped for about a second three miles from airport when I turned off fuel booster pump. Recoverd, but only partial (~60%) power. I could hear a hum of varying pitch and intensity under cowl. Turning booster pump back on helped some. Made it back to home base (ATW) OK.
Check under cowl revealed nothing unusual. No fuel, odor, nothing loose.

Any ideas, suggestions? 

[montanapilot]

I had a similar problem, although not quite so severe. My engine began to sputter about 500' off the ground on takeoff. I reduced power and it became smooth. I tried advancing power again and it again became rough. That quickly became probably my shortest airplane flight in 57 years. I find that by far the best (only, for me) source of diagnosis is the horse's mouth - Lockwood. They are very available, very willing to help, and extremely knowledgeable. In my case, it was very simple. The nuts on the carb bowls can become loose - just a very small amount. Dean at Lockwood suggested that my mechanic check the torque on the nuts. They were both only very slightly loose, but after he tightened them, the engine ran perfectly. I would only caution that just because this was the issue with my engine, that doesn't mean it's the same with yours. I highly recommend calling Lockwood and describing all that happened. Hopefully, it will be an easy fix like mine.

[Cluemeister]

I have previously documented my turbo carb bowl issue, now resolved. Your issue sounds different, but I would recommend calling Lockwood as well.

[podpilot]

Thanks.
Did you hear a hum also, like leaking air?

[Flocker]

Were you in "turbo" mode when it happened?

[Cluemeister]

My issue was sputtering when applying full turbo (115%). Turns out the carb bowls weren’t sealed tightly enough for that much pressure. The first attemptsed solution was to tighten them to spec, but when that didn’t work, it was later discovered they were warped and needed replacing.

[buzz]

Jul 16, 2018 23:52:00 GMT podpilot said:

Tecnam Astore 2015, ~150 hours, Rotax 914 turbo. Flown 20 hours since annual in March Without any issues. Flying today, July 16, 2018; Engine stopped for about a second three miles from airport when I turned off fuel booster pump. Recoverd, but only partial (~60%) power. I could hear a hum of varying pitch and intensity under cowl. Turning booster pump back on helped some. Made it back to home base (ATW) OK.
Check under cowl revealed nothing unusual. No fuel, odor, nothing loose.

Any ideas, suggestions? 

Yikes that's scary when that kind of thing happens. I'm not an A@P so my comments are untrained guesses. I was wondering if you have an issue with the primary fuel pump. Sounds like you turned on the Aux pump for take off then turned it off per normal operation, then you had the problem. The pumps do make some noise when they run. Have you checked to see if the primary is working correctly?

For that matter I'm curious about your fuel flow. Maybe check to ensure no obstructions such as a clogged strainer in the gascolator or other location. I had this happen when my plane was brand new and it almost put me in the weeds. Only seemed to have been temporarily remedied by turning on the Aux pump. As I said before the pumps do make some noise and I would bet they make more noise if a pump was cavitating from lack of fuel flow.

Just my 2 cents as I said I'm no expert so I could be way off. Hope things get figured out good luck.

[Flocker]

Clue, any chance this is a sticky waste gate issue?

[Cluemeister]

I would head over to rotax-owner.com and post the question on that forum. Lots of experienced rotax guys over there.

[podpilot]

I appreciate the advice

The turbo is always on in the 914. I did not use the "Boost Mode" taking off that day. When the problem occurred, the OAT was 88F. The engine ran fine on take off and climb out until I turned off the boost pump. It then died for a second, then recovered with partial power. Turning boost pump back on made little improvement. Switching tanks did nothing. The gauges were all in the green including the fuel pressure.

One person has told me that it may have been a vapor lock issue. I burn 91 octane ethanol free auto gas.

I ran it up on the ground for 15 minutes yesterday, (OAT 77F). There was one slight hesitation but not the drama of Monday. Fuel pressure, CHT, oil pressure and temp all fine. Turbo worked fine.

A fuel flow issue should not be affected by OAT correct? Nor should it occur only while flying?

[montanapilot]

Call Lockwood.

[ChiMike]

I have a P2008 turbo. The age of your fuel —Mogas with alcohol added up to 10% —could have been a factor: a variant of yiurvissue happened to me last summer. Refilled with 100LL and no similar issues until last winter when it was determined to be the carb bowls and floats /gaskets. So you may have a combination problem.

But try using Avgas and see if that gets any alcohol that’s breaking down into water vapor out of the system. If that does the trick then perhaps look for mogas that is recently delivered to the service station. Obviously your storage or letting the plane set a long time could impact the fuel as well.

Curious what others think of this?

[podpilot]

I burn mostly 91 octane alcohol free auto gas (Shell). Fuel tanks were full at the time. I flew the plane on a long cross country to New Mexico in May burning 100LL for most of trip and experienced no problems.

What I would like is a check list of things to inspect/correct before I fly again.

I have retrieved information from people at Sebring, Florida, Service center in Minnesota, my local mechanic and two online forums including this one. Advice so far:

Carburetor drain plugs with improper torque

Fuel flow problem

Bad, winter blend auto fuel

Water in fuel (Was never seen in sumps)

Vapor lock (Incident occurred on relatively hot day, 88F)

Possibly loose carb injectors

Any additional advice is appreciated

[CharlieT]

You indicated the problem started when you turned off the #2 boost pump, to me this would indicate a fuel problem. Why couldn't the #1 pump keep up? I would start by removing the filter/screen in the gasolator on the fwd lower right firewall. While the bowl is off you mite do a quick check of the fuel flow with each pump and a bucket to catch the full. Its a start!

[podpilot]

My appreciation to all who helped with my Rotax 914 turbo issue.

I got all the information I could from several sources: This thread, the dealer in Florida, the certified maintenance shop who did the annual, and at least eight people at the Rotax, Tecnam, Lockwood, and Leading Edge vendor tents at the EAA convention.

My local mechanic and I went through my checklist:

Gascolator

Fuel screens

Carburetor bowl mounting screws

Carb bowl gaskets

Carb floats

Fuel flow

Fuel pumps (2)

There was a slight "varnish" on the carburetor bowls suggestive of a fuel leak. The mounting bolts were a bit loose, below spec with torque. The bowl gaskets were of the fiber type. There were exchanged for rubber ones purchased at EAA. We also added a spring under the bowl. This spring, I believe,  is the only thing that holds the bowl on Rotax 912 engines which do not have the bolt.

Everything else checked out fine.

I have since flown the Tecnam Astore for three flights, one hour each,  without a problem. Two flights were on days as hot or hotter than the day I experienced the partial engine failure.