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Wondering if any other Astar operators are having problems with their engines because of this "fuel coking" problem. We've been through one engine already on our B3 and a B2 in our company is needing another engine after the first couple are having the same coking problem.

 

We're trying the experimental cranking the engine after shutdown to get the fuel out of the bearing but don't really know if this will work until a thousand more hours.

 

Any comments?

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Turbomeca's are known to coke the oil in the rear bearing, but this is the first I've heard of a "fuel" coking problem. Please elaborate a bit more. What happens and where does the coking occur? Does the coking culminate in a complete failure? Are there any signs of trouble prior to failure (such as deteriorating power checks, etc)? What does AEC (or, for that matter, TEC) say? Do you use any fuel additives? Jet-A or Jet-B or other?
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I've heard of that rear bearing coking up too (that's why you are not suppose to idle for very long). This I was told is different.

 

The Turbomeca Tech Rep said they tried different fuel additives to try and prevent the fuel coking problem but they found it was eating away the rubber o-rings. They redesigned a bearing and started to install them in some engines but found they didn't help at all. I'm not that savy about it but my understanding is that the fuel is "trapped" in a certain area which ends up remaining very hot even after shutdown. The fuel cokes up there and causes problems. It's been a known problem (I was told) for many years but they have not found a solution that works yet. Yes, your powercheck will get worse and worse slowly.

 

By the way, as350 I found a MMEL for your 206. It's posted in the other message.

 

-Rey

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Rey haven't had any problems on the Astars that I have been flying or the Lama engine, but last fall I was doing a seismic job in Wyoming with an L-3 and it coked the engine breather. I started to notice a dirty exhaust(which the C-30P is really dirty anyway) then started blowing oil out about as fast as we could put it in. The breather at the bottom of the C-30 that looks like an exhaust pipe off your lawn mower was coked soild. The mech cleaned it and worked fine afterward. Can your Mechs check for something similar with your engines? Jesse
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Yes. Our mechanic knows when the fuel coking thing is happening but there isn't anything to prevent it from happening yet. The engine runs fine it just slowly starts to lose efficiency.

 

On a side note: I had a C-20 coke up after a relief pilot shut it down without a 2 minute cool down several times. I went to preflight and the rotor wouldn't turn backwards. Started the engine for a few seconds then shut it down.  It was enough to loosen up the stuff and I did a normal start after.

 

The fuel coking in the Turbomeca s different than the normal oil coking (at least that is what I was told). I'm not an expert on this at all though.

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  • 3 weeks later...

Apparently, "fuel coking" is a made-up term offered by the Southwestern Tech Rep.  Here's what 'lil bit I know about the subject.

 

One night we had an uneventful B3 flight to the "Rez", then Tucson and back.  Three starts and three shutdowns.  No prolonged idling.  A couple of hours later we received and Inter-facility call.    When I attempted to start the engine all I got was a dimming of the instrument lights and a big draw down on the battery.  After several attempts, we aborted and called maintenance.  

 

After the aircraft was low-boy'd to the hanger it was quickly discovered the the starter generator was working just fine.  The eventual engine breakdown revealed what one mechanic described as the gas generator wheel "cemented to the case" by what looked like petrified dirt.

 

The Tech Rep was quick to suspect "bad fuel and poor sand filters".  He went so far as to sight similar incidents in Southern Arizona to substantiate his "bad fuel" theory.  The sand filter may be a "poor" design (I don't really know) but it was functioning properly.

 

Since that engine had only been installed for 40 something hours, (our 5th or 6th engine for that aircraft in two years) we suspected that the problem was well on it's way before we got it from Turbomecca.  We later found-out that it had previously been installed in an EMS bird in Sierra Vista.  Sound familiar?  Apparently, it hadn't been inspected prior to its delivery to us.  The acute shortage of Arriel 2B engines coupled with the high demand for replacements has caused Turbomecca some big problems.  Thank god for "Power by the Hour"!

 

Two years ago I pulled the following from the Turbomecca FAQ page:

 

"There is no maximum time limit required at ground idle speed prior to shut down. However, it has been noticed that operation at ground idle for more than 5 minutes may be detrimental to the cocking process of the gas generator rear bearing. This may prevent you from deleting the 1000 hour rear bearing cleaning as defined by the Service Letter # 1848. However, if your permeability checks results are good, you may skip this 1000 hour cleaning. This is why we recommend not exceeding 5 minutes at ground idle before shut down."

 

We've taken this recommendation one step further by taking the engine to "fly" if we're at a scene for more than 5-min's.  We leave it there for 3-min's before going back to "idle" and repeat as necessary.  Some pilots don't go to idle at all, not even prior to shutdown.  

 

As a result of our "fuel coking" event, our Area Manager has put out a Memo requiring pilots to turn the sand filter on for at least three minutes during each enroute leg of flight.  Needless to say, it's always on when we land in the desert.

 

Anyway, YES there is a thing called "fuel coking", and it's happened to at least one other aircraft.  Frankly, I doubt it's got anything to do with "bad fuel" as we don't get gas where the previous user did.  Maybe it's just a problem with that particular engine.  Who knows?  One thing I do know, it sure does make this pilot think twice about shutting-down on those near-border scenes at 2 AM.

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Sure sounds familiar JAM. We are on our 3rd 2B engine now. History of our engine is it was probably in your ship at one time also! I think they just rotate engines around the Southwest hoping someone won't complain. I think our engine is the one that blew up in Showlow. Now we are getting a yellow GOV light: Sometimes blinking, sometimes steady, always annoying. To solve the problem they are giving us another engine. Wonder what the problem will be with the next one...
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Sure sounds familiar JAM. We are on our 3rd 2B engine now. History of our engine is it was probably in your ship at one time also! I think they just rotate engines around the Southwest hoping someone won't complain. I think our engine is the one that blew up in Showlow. Now we are getting a yellow GOV light: Sometimes blinking, sometimes steady, always annoying. To solve the problem they are giving us another engine. Wonder what the problem will be with the next one...

I don't know the lineage of the Showlow engine, but the one with "fuel coking" went from one of our aircraft to Sierra Vista before eventually returning to us.  Apparently engine shortages don't allow Turbomecca much time for inspection prior to reissue.

 

I keep reading that Turbomecca has hot new plans to improve service and availability, but it's hard to see at the user level.  If the current un-reliability trend continues, their reputation will dip beyond recovery.  For many of us, it's there now!

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I heard a rumor that a helicopter company in Alaska stopped using B3's because they were too unreliable and were not field proven with the FADEC and 2B engine (They went back to all B2's). I would hate to have a B3 in the Interior wondering when "fuel coking" would happen or waiting for a Tech to show up in Kaltag when the engine started going Tango Uniform again.
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We also have a new 2B engine in our B3. I think I know which ship you are talking about in AZ.

 

So far, our 'new' engine hasn't had any new x-mas lights blinking on the caution panel... yet... knock on wood...

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  • 3 months later...

Apparently, Turbomecca is sticking with they're "bad fuel" cause for coking.  Now they're recommending the use of Prist for all refueling.  Assuming that icing isn't the problem in Arizona, the French must be fungi phoebic.  

 

Undoubtedly the next "fuel coking" incident will be blamed on Ozone depletion, El Nino or solar flares.     :devil:

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  • 2 months later...

Another long dead thread back to the top.

 

The program that I used to fly for in ABQ had a very similar problem with coking on their B2 several years ago (they later switched to a B3). They went throught the same round of excuses from the TM tech reps before the med. crew just refused to fly it until they got a whole new engine. It would just refuse to start if it had been recently shut down.

 

Funny how the same bag of lame excuses just keeps popping up from the TM guys when its a know issue. Some engines just seem prone to it for some reason, and once they start there seems to be nothing you can do to fix it except replace the whole thing.

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Rey - Temsco in Juneau had B3s when I visited but they were not happy with them as on more than one occasion, when the outside temp dropped below limits the FADEC system wouldnt start, so there they were out the back somewhere on a pilots choice tour and the engine wont start.

 

From those in the know this happened more than once and now the B2s are the primary aircraft for pilots choice tours and the B3s are kept for the sling work and the group tours to the Mendenhall glacier and others close by.

 

Heli Ops  :devil:

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  • 5 months later...
Concerning AS 350 B model squirrels. Have had problems with starting via the manual of 10-12% engage fuel flow BUT our B hangs till n1 hits up to 20+n1 THEN bang its like the back end being blowing off, usual shut down, inspect, report testing new igniters, fuel flow checks, etc etc still does it, BUT solution we have found is progressing the fuel flow lever to idle then starting and managing T4 etc in limits and get a 'NORMAL' squirrel start with gradual smooth progress off temps etc. If you forget or new pilot starts it by the book it will get another hang/ hot start were T4 will race over limits and if you are not expecting it you will cook it. Tech rep, Engineering manager - good old words - monitor/ let it develope. Does anybody have ideas about this, apperantly 3 machines in New Zealand and 2 in Oz having same problem. Advice appreciated   :confused:
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One solution to the hot starts on 350-B models is to perform the "cold weather start" during the first start of the day. All subsequent starts are normal (wait until 10% Ng before advancing Fuel Flow Control).

Very high OAT seems to agravate the starting problems and the T4 will be higher (sometimes up to 750 celsius) for continuous Ng increase.

BA and B2 helicopters don't exhibit this oddity.

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