Bell 206: JetRanger and LongRanger
Join Date: Feb 2002
Location: N20,W99
Age: 53
Posts: 1,119
Likes: 0
Received 0 Likes
on
0 Posts
There are also several indications of this described malfunction, the most obvious one would be that if you are burning extra oil in the combustion chamber your TOT (turbine outlet temp.) is very likely to rise considerably! You are also going to lose oil pressure quickly, and more so if it is burning at a rate that will consume 5.2 liters in a few minutes, like described!
I guess it could be argued by many if this was an engine fire or not, my opinion is an engine fire is when there is fire in the engine compartment.
Shawn said if you had a fire detection system you would know? but most engine fire detection systems are the "melting wire" type running inside the engine compartement that turn on the light in the cockpit, but how is that going to work with the engine burning oil internally? Even if you had the engine fire detection kit you could probably not get warning, so is it an engine fire or an engine burning oil?
I guess it could be argued by many if this was an engine fire or not, my opinion is an engine fire is when there is fire in the engine compartment.
Shawn said if you had a fire detection system you would know? but most engine fire detection systems are the "melting wire" type running inside the engine compartement that turn on the light in the cockpit, but how is that going to work with the engine burning oil internally? Even if you had the engine fire detection kit you could probably not get warning, so is it an engine fire or an engine burning oil?
Join Date: Jan 2003
Location: South East England
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
OK - Engine burning oil. Tell that to the Firemen who turned up and wanted to put the flames out, or tell that to the CAA bloke who was in receipt of the M.O.R !
Oh I see - Sorry.
Because the whole bloody thing did'nt go up in flames it's not a fire, Right.
Next time I'll jump out and throw a few gallons of fuel on it.
Oh I see - Sorry.
Because the whole bloody thing did'nt go up in flames it's not a fire, Right.
Next time I'll jump out and throw a few gallons of fuel on it.
This is unusual - I agree with something PPF#1 has said! One of us has changed!
Yes he is spot on. It ain't an engine fire - the engine is behaving relatively normally, albeit with a lot of oil going down its gullet. If there was a fire detection system on a 206, it would not detect anything in this case, and if there were an extinguishing system, activating it would achieve absolutely zero positive results.
You were lucky to have somebody tell you about the smoke, and it saved you the stress of the oil pressure failure and the eventual engine seizure - instead you had a Happy Landing. Buy the controller a lottery ticket, and get one for yourself.
Yes he is spot on. It ain't an engine fire - the engine is behaving relatively normally, albeit with a lot of oil going down its gullet. If there was a fire detection system on a 206, it would not detect anything in this case, and if there were an extinguishing system, activating it would achieve absolutely zero positive results.
You were lucky to have somebody tell you about the smoke, and it saved you the stress of the oil pressure failure and the eventual engine seizure - instead you had a Happy Landing. Buy the controller a lottery ticket, and get one for yourself.
Join Date: Jul 2000
Location: The Daylight Saving Free Zone
Posts: 733
Likes: 0
Received 0 Likes
on
0 Posts
quote:
--------------------------------------------------------------------------------
sprocket wrote:
I was unfortunate to have an in-flight engine fire on a B206 last Saturday.
There were no indications from the T's & P's, and on landing the fire worsened, presumably because power was being reduced. It got even worse when I shut down to flight idle.
It now transpired that a Turbine seal had given up, allowing oil from the header tank into the combustion chamber and therefore igniting.
I was informed that if the flight had continued for another 10 – 15 minutes, the Donkey would have stopped due to lack of oil.
For future reference, apart from low oil pressure, high oil temp, what other symptoms would/could there have been to have warned me?
--------------------------------------------------------------------------------
sprocket wrote:
I was unfortunate to have an in-flight engine fire on a B206 last Saturday.
There were no indications from the T's & P's, and on landing the fire worsened, presumably because power was being reduced. It got even worse when I shut down to flight idle.
It now transpired that a Turbine seal had given up, allowing oil from the header tank into the combustion chamber and therefore igniting.
I was informed that if the flight had continued for another 10 – 15 minutes, the Donkey would have stopped due to lack of oil.
For future reference, apart from low oil pressure, high oil temp, what other symptoms would/could there have been to have warned me?
sprocket actually did write:
Oops! Sorry, shprocket. You're right, it was Happy Landing ! As my kids say, my bad. My face is red.
To Happy Landing ! and Blender: I actually did have a similar bearing failure while hovering out for departure in a ship equipped with two C-20B's and did not notice anything unusual with the TOT gauges. The fire-warning lights were dark. Over the radio came a surprisingly calm message, "Hey boss, you're on fire," which everybody onboard heard of course because they all had headsets. I looked down at my shadow, saw the plume, knew what it was and put her down. As soon as I stopped the forward motion the smoke caught up with us and we were enveloped in a white/gray cloud. Man, you should've seen my pax un-ass the a/c. They jumped out like it was on fire! They ran away a safe distance then looked back, astounded that I hadn't leapt out too. But hey, the good engine still needed a two-minute cooldown. No sense screwing up both of them.
Happy, you got lucky. In the first place it wasn't a "fire" (i.e. no danger of airframe involvement) despite what the firemen thought. In the second place, you were notified early enough that you didn't get to perform an actual EOL. Count your blessings.
Did I really say that??
To Happy Landing ! and Blender: I actually did have a similar bearing failure while hovering out for departure in a ship equipped with two C-20B's and did not notice anything unusual with the TOT gauges. The fire-warning lights were dark. Over the radio came a surprisingly calm message, "Hey boss, you're on fire," which everybody onboard heard of course because they all had headsets. I looked down at my shadow, saw the plume, knew what it was and put her down. As soon as I stopped the forward motion the smoke caught up with us and we were enveloped in a white/gray cloud. Man, you should've seen my pax un-ass the a/c. They jumped out like it was on fire! They ran away a safe distance then looked back, astounded that I hadn't leapt out too. But hey, the good engine still needed a two-minute cooldown. No sense screwing up both of them.
Happy, you got lucky. In the first place it wasn't a "fire" (i.e. no danger of airframe involvement) despite what the firemen thought. In the second place, you were notified early enough that you didn't get to perform an actual EOL. Count your blessings.
Join Date: Jul 2002
Location: CH
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
To be clear:
Internal oil leak in the engine? Love to know which one for interest. The seal must have come apart big time. I seriously doubt that you will see any noticeable change in the TOT. I have run all of the allowed fuels in a 250 and never seen any difference.
As for the T & P's. It is a fallacy that low oil quantity will give you a high oil temp. Simple physics tells you that with LESS oil it goes via the cooler more in a given period of time, so lower temp. Applies the same on piston engines as well. By the time the pump runs dry there will be no oil in the return line to show you the temp.
Classic is the B 206. People don't read the manual and fill the MGB till there is a bubble at the top of the sight glass. WRONG! Full is halfway up the sight glass. Fly a 206 hard at high temps (firefighting)and watch the MGB Temp approach the limits - solution - remove oil until it is just visible in the bottom of the glass. No more problems.
Internal oil leak in the engine? Love to know which one for interest. The seal must have come apart big time. I seriously doubt that you will see any noticeable change in the TOT. I have run all of the allowed fuels in a 250 and never seen any difference.
As for the T & P's. It is a fallacy that low oil quantity will give you a high oil temp. Simple physics tells you that with LESS oil it goes via the cooler more in a given period of time, so lower temp. Applies the same on piston engines as well. By the time the pump runs dry there will be no oil in the return line to show you the temp.
Classic is the B 206. People don't read the manual and fill the MGB till there is a bubble at the top of the sight glass. WRONG! Full is halfway up the sight glass. Fly a 206 hard at high temps (firefighting)and watch the MGB Temp approach the limits - solution - remove oil until it is just visible in the bottom of the glass. No more problems.
Saw a case when the 206 MGB was overfilled and the oil frothed and the pressure dropped way below limits and brought on warnings. Same fixit, drain out the extra oil.
Join Date: Jul 2002
Location: Up a sago palm
Posts: 35
Likes: 0
Received 0 Likes
on
0 Posts
John,
As far as I am aware the oil does not get circulated through the cooler in a separate faster cycle, so why would the temp be lower if the oil is also going through the engine at a proportional rate to the cooler? If all the oil is not being burnt as it arrives at the engine then I believe you will see a negligible overall effect to the oil temperature until the oil level is too low to draw up.
The point you make regarding the transmission oil temperature is irrelevant to what was going on in the engine. Not sure why you put that one in. I presume it is because of your figjam approach to discussions.
I too have had the oil exit a 206 in flight. The only indication I had was fluctuating oil pressure when presumably the oil level reached the pickup in the tank. There was a corresponding increase in oil temperature from that point on.
Cheers
The point you make regarding the transmission oil temperature is irrelevant to what was going on in the engine. Not sure why you put that one in. I presume it is because of your figjam approach to discussions.
I too have had the oil exit a 206 in flight. The only indication I had was fluctuating oil pressure when presumably the oil level reached the pickup in the tank. There was a corresponding increase in oil temperature from that point on.
Cheers
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
The internal oil seal failure is actually a very very bad thing to happen, even if the oil never leaves the engine. Here's why:
The oil enters the airpath and gets misted into the fuel/air mixture. It burns, and adds its energy to the situation. This does not cause the tot to run hotter, because the fuel control cuts back the fuel to exactly the right proportion to maintain proper N2 rpm. This means that you save gas because you are burning oil instead. So far, no sweat until you run out of oil.
But if the seal gets worse (they always do) then the oil leaks faster, and then faster. If the oil leak gets to be as much as the fuel flow should have been, then the fuel control will cut all the way to idle. If you lower the lever or if the oil leak gets worse, than the engine will run away, and the overspeed protection will be no help at all (it will cut the fuel, but that's not what is burning!
This has happened, and it usually leads to an explosive runaway, where the engine comes apart.
The oil enters the airpath and gets misted into the fuel/air mixture. It burns, and adds its energy to the situation. This does not cause the tot to run hotter, because the fuel control cuts back the fuel to exactly the right proportion to maintain proper N2 rpm. This means that you save gas because you are burning oil instead. So far, no sweat until you run out of oil.
But if the seal gets worse (they always do) then the oil leaks faster, and then faster. If the oil leak gets to be as much as the fuel flow should have been, then the fuel control will cut all the way to idle. If you lower the lever or if the oil leak gets worse, than the engine will run away, and the overspeed protection will be no help at all (it will cut the fuel, but that's not what is burning!
This has happened, and it usually leads to an explosive runaway, where the engine comes apart.
Join Date: Aug 2002
Location: Australia
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
You haven't said which seal failed but if it was your #5 bearing seal that gave up (most likely) you would have had no increase in temperature indications as they are downstream of the TOT probes. When you wound it down to ground idle the balancing air would have been reduced and allowed even more oil to pump past the seal making the smoking worse. Other factors to look at was the seal showing any indications on flights prior to yours that it was U/S (when it usually is on it's way out produces a large smoke puff on shut down and smoking on start). You did say it was a turbine seal but if there was a small increase in TOT it could point to the #1 bearing leaking but it would be so small you would not be able to notice the rise anyhow.
Technically is was not a fire but a bearing failure but the fire fighters did the right thing as when they see smoke they think fire and you are lucky that they were there just in case something worse happened. If you did run out of oil things would have turned really nasty really fast, caution panel would have lit up like a christmas tree.. oil temp, oil pressure.. perhaps chips as bearings failed, oil pressure guage fluctuates with cavitation in the pump then falls, nasty noises as donk lets go and top it all of with an auto with eng horn blaring and eng fail light glowing a lovely shade of red... that's if your donk's wheel hasn't chopped your blade in two.
Technically is was not a fire but a bearing failure but the fire fighters did the right thing as when they see smoke they think fire and you are lucky that they were there just in case something worse happened. If you did run out of oil things would have turned really nasty really fast, caution panel would have lit up like a christmas tree.. oil temp, oil pressure.. perhaps chips as bearings failed, oil pressure guage fluctuates with cavitation in the pump then falls, nasty noises as donk lets go and top it all of with an auto with eng horn blaring and eng fail light glowing a lovely shade of red... that's if your donk's wheel hasn't chopped your blade in two.
Join Date: Jun 2001
Location: Australia
Posts: 251
Likes: 0
Received 0 Likes
on
0 Posts
John Bicker
wouldnt 'simple physics' say that the oil cooler only cools a % of the total cooling effect? the reservior is an oil cooler and so is the crankcase. surly more oil in these should make cooling an easier job.
i know nothing of this MGB (main rotor gearbox i prisume) but is it possible the temp sender doesnt get enough oil splashed onto it to read corectly? with more oil in the sump of anything, more heat can be transfered to the outer case and to atmosphear.
i know nothing of this MGB (main rotor gearbox i prisume) but is it possible the temp sender doesnt get enough oil splashed onto it to read corectly? with more oil in the sump of anything, more heat can be transfered to the outer case and to atmosphear.
Join Date: Jul 2000
Location: The Daylight Saving Free Zone
Posts: 733
Likes: 0
Received 0 Likes
on
0 Posts
vorticey: It is a known symptom with overfilling 206 T/Ms.
As the oil is not stored in a separate tank, the higher oil level in the T/M enables aeriation/foaming to occur (it gets stirred up by the gears).
The efficiency of the pump is reduced because it is pumping a lot of air and also a lot of oil can get vented overboard (and for some reason most of it does when the level starts off way too high).
Nick: it all depends (as bellsux said) on where the leak is …
If the #8 brg seal (labyrinth type) or its sump leaked oil, it would be closest to the combustion.
It would burn but not “efficiently” as it has not been “atomised” by the fuel nozzle or being mixed to some extent if coming from a compressor bearing .
I suspect that if it were a significant leak, it would give a higher TOT indication without performance increase.
As the oil is not stored in a separate tank, the higher oil level in the T/M enables aeriation/foaming to occur (it gets stirred up by the gears).
The efficiency of the pump is reduced because it is pumping a lot of air and also a lot of oil can get vented overboard (and for some reason most of it does when the level starts off way too high).
Nick: it all depends (as bellsux said) on where the leak is …
If the #8 brg seal (labyrinth type) or its sump leaked oil, it would be closest to the combustion.
It would burn but not “efficiently” as it has not been “atomised” by the fuel nozzle or being mixed to some extent if coming from a compressor bearing .
I suspect that if it were a significant leak, it would give a higher TOT indication without performance increase.
Join Date: Jan 2003
Location: South East England
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
Well Thank you One and All....
The ship had just had a star annual (3.5 hrs total flown to "Seal malfunction").
The Hot section has now been removed, and it was the 5th wheel bearing.
Absolutly no indications in the front, and no smoke on startup/shut down that I noticed.
It was planned that day to pick up another Pax rotors running, then head off to the Breacon Beacons for some fun !
Judging by what has been said here (Thank you), I should have got a lottery ticket that day.
Ah well, back to the R44 for a while
Happy
The ship had just had a star annual (3.5 hrs total flown to "Seal malfunction").
The Hot section has now been removed, and it was the 5th wheel bearing.
Absolutly no indications in the front, and no smoke on startup/shut down that I noticed.
It was planned that day to pick up another Pax rotors running, then head off to the Breacon Beacons for some fun !
Judging by what has been said here (Thank you), I should have got a lottery ticket that day.
Ah well, back to the R44 for a while
Happy
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
sprocket,
If the leak gets into the combustion section, it will burn, and when it does, it replaces fuel. This is a classic engine runaway scenario. Another way to make your engine go this way is to leak any conbustable into the inlet. This is what happened to the V-22 that shattered an engine over the Potomac. A leak built up in the inlet, and when the engines were tilted back, the fluid poured into the engine, causing a destructive overspeed that was unpreventable with the normal overspeed shutdown.
A typical Allison burns about .5 lb/hr/SHP, so if it were at 65% power, about 200 HP, it would burn 100 lb/Hr. That is 16 gallons per hour, or 1 quart of fuel a minute. If the engine starts leaking at 1/2 quart per minute, and the pilot lowers the collective to descend at 25% power, the engine will run away and probably destruct.
If the leak gets into the combustion section, it will burn, and when it does, it replaces fuel. This is a classic engine runaway scenario. Another way to make your engine go this way is to leak any conbustable into the inlet. This is what happened to the V-22 that shattered an engine over the Potomac. A leak built up in the inlet, and when the engines were tilted back, the fluid poured into the engine, causing a destructive overspeed that was unpreventable with the normal overspeed shutdown.
A typical Allison burns about .5 lb/hr/SHP, so if it were at 65% power, about 200 HP, it would burn 100 lb/Hr. That is 16 gallons per hour, or 1 quart of fuel a minute. If the engine starts leaking at 1/2 quart per minute, and the pilot lowers the collective to descend at 25% power, the engine will run away and probably destruct.
Nick - I wonder why this sort of info isn't readily available??
I have been flying turbines for 34 years now, and this thread is the first time i have ever seen this information. A bit scary that "shutting down" the engine will have no effect and it will burst its breeches with a cloud of dust and a hearty "hi-ho Silver".
It should be taught in any turbine ground school. I have done the Allison school a couple of times and they didn't talk about a major internal leak at all.
A marketing opportunity for Shawn Coyle and a new book!! I will take my usual 10% thanks...
I have been flying turbines for 34 years now, and this thread is the first time i have ever seen this information. A bit scary that "shutting down" the engine will have no effect and it will burst its breeches with a cloud of dust and a hearty "hi-ho Silver".
It should be taught in any turbine ground school. I have done the Allison school a couple of times and they didn't talk about a major internal leak at all.
A marketing opportunity for Shawn Coyle and a new book!! I will take my usual 10% thanks...
Exact thing happened to me in a 206L-1 in the early eighties. There was no indication of anything wrong in the cockpit, but billows of black smoke were pumping out of the can. With no place to land (Northen Quebec) I flew for a few minutes before finding a clearing, and actually started to see a lowering oil pressure prior to shutting her down. It makes for a very long few minutes when you know something bad is going to happen very shortly and you're over nothing but trees.
Join Date: Jul 2002
Location: CH
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
AC,
Get your hands black Rob with all that spare time, Stud won't mind. Ask him about the early days of the C30 engine in the A model and why thay had large lumps of steel inside the engine cowlings.
To go back to my original post - I still think that as HL said " the T & P's showed nothing abnormal" and with the proviso in this case until it actually ran out of oil there is no reason to.
As to the claims of higher TOT in this case as we now know it was downstream of the thermocouples so there would be no indications. As to the higher TOT claims with oil leaking in before the thermocouples - why? This is a heat engine, if you release x kJ of energy you get what you pay for and the temperature would remain the same. The flow would change in the FCU to remain at the same output because the engine cannot do something all of a sudden for free, the efficiency of the engine doesn't change. The heat value may vary slightly from one fuel to another but the amount of energy released must remain the same so it may take more or less fuel/oil. In the case that NL makes the fuel, in this case oil, is uncontrolled. Yes it will come apart.
The oil system in the Allison is sensitive to any abuse from the operator and the mantainer. The 6 & 7 bearing areas can suffer from lack of oil (blocked jet) and too much oil (blocked scavenge). Both are critical. The blocked jet scenario will lead to a bearing failure so fast you probably won't see anything abnormal. The bearings will come apart or melt to the point that the pieces are too big to fit down the scavenge to get to the chip detector. The blocked scavenge will flood the space and lead to the explosive failure as described by NL. The #8 bearing is capable of the same. In the case of a pure leak (i.e. mechanical) in this area you will actually lose air from the engine and end up with high TOT and loss of performance the oil will not leak out when the engine is running, it will with a blocked scavenge though or in the previous case on shutdown.
Regarding the "lower oil temp with less oil". This is still the case as the mass to be cooled is reduced. The "example" of the 206 gearbox is that it is a very simple system which has thermostatic control and can reach temperature limits even without the quoted "foaming". Why does more oil leave the gearbox once it is aerated? Because it takes time to de-aerate - simple.
The problem is the delta T to be achieved. For instance if the cooler was 100% efficient it cannot lower the temperature below the cooling medium which in this case is air. The thermovalve complicates the issue slightly as it is trying to increase the oil temperature, when it reaches its limit you are then stuck with the difference achievable in temperature as described up to the limits of the oil. For example if you increase the size of the cooler or reduce the amount of oil (mass) the result is the same. Look at it this way, you have 2 buckets of water, one hot, one cold, the cold one in this case is the cooler and it's size is fixed. The hot one is the transmission oil which has a heater in it and we are making it larger or smaller. What happens when we mix the two together and look at the resultant temperature? Heat energy in its pure form cannot be made or destroyed just moved - First Law of Thermodynamics. The rate through the cooler is constant and with more oil in the transmission it stays there longer to absorb more heat.
That's the way I see it - End modified rant.
Get your hands black Rob with all that spare time, Stud won't mind. Ask him about the early days of the C30 engine in the A model and why thay had large lumps of steel inside the engine cowlings.
To go back to my original post - I still think that as HL said " the T & P's showed nothing abnormal" and with the proviso in this case until it actually ran out of oil there is no reason to.
As to the claims of higher TOT in this case as we now know it was downstream of the thermocouples so there would be no indications. As to the higher TOT claims with oil leaking in before the thermocouples - why? This is a heat engine, if you release x kJ of energy you get what you pay for and the temperature would remain the same. The flow would change in the FCU to remain at the same output because the engine cannot do something all of a sudden for free, the efficiency of the engine doesn't change. The heat value may vary slightly from one fuel to another but the amount of energy released must remain the same so it may take more or less fuel/oil. In the case that NL makes the fuel, in this case oil, is uncontrolled. Yes it will come apart.
The oil system in the Allison is sensitive to any abuse from the operator and the mantainer. The 6 & 7 bearing areas can suffer from lack of oil (blocked jet) and too much oil (blocked scavenge). Both are critical. The blocked jet scenario will lead to a bearing failure so fast you probably won't see anything abnormal. The bearings will come apart or melt to the point that the pieces are too big to fit down the scavenge to get to the chip detector. The blocked scavenge will flood the space and lead to the explosive failure as described by NL. The #8 bearing is capable of the same. In the case of a pure leak (i.e. mechanical) in this area you will actually lose air from the engine and end up with high TOT and loss of performance the oil will not leak out when the engine is running, it will with a blocked scavenge though or in the previous case on shutdown.
Regarding the "lower oil temp with less oil". This is still the case as the mass to be cooled is reduced. The "example" of the 206 gearbox is that it is a very simple system which has thermostatic control and can reach temperature limits even without the quoted "foaming". Why does more oil leave the gearbox once it is aerated? Because it takes time to de-aerate - simple.
The problem is the delta T to be achieved. For instance if the cooler was 100% efficient it cannot lower the temperature below the cooling medium which in this case is air. The thermovalve complicates the issue slightly as it is trying to increase the oil temperature, when it reaches its limit you are then stuck with the difference achievable in temperature as described up to the limits of the oil. For example if you increase the size of the cooler or reduce the amount of oil (mass) the result is the same. Look at it this way, you have 2 buckets of water, one hot, one cold, the cold one in this case is the cooler and it's size is fixed. The hot one is the transmission oil which has a heater in it and we are making it larger or smaller. What happens when we mix the two together and look at the resultant temperature? Heat energy in its pure form cannot be made or destroyed just moved - First Law of Thermodynamics. The rate through the cooler is constant and with more oil in the transmission it stays there longer to absorb more heat.
That's the way I see it - End modified rant.
Last edited by John Bicker; 12th Jun 2003 at 23:24.
"Oh, look mommy, that helicopter is skywriting!"
Ascend Charlie asked:
That's because:
A) It's not a problem to worry about; and
B) It doesn't happen.
Well, I take that back - we've all seen some massive internal oil leaks caused by bearing or seal failures. Happy Landing ! can attest to that. But Nick's theory is that an engine could develop an oil leak so bad that the flow of oil could exceed that of the fuel...and that the engine would happily run exclusively on that oil while the FC took a break and ran itself back to idle.
Umm... Well, maybe...if we had a humongous oil supply.
The RR/Allison 250-C20B in my aircraft consumes about 25 gallons of fuel per hour in cruise. This means that a tad over 1.6 quarts of fuel are being slurped every minute. If the engine should "suddenly" switch over and start using oil instead of fuel, how long do we think it would run before exhausting the oil supply? I'd be completely out of oil in under four minutes. How much oil does *your* system hold?
Trouble is, we wouldn't even be starting from 100% full, even if the tank was filled to the very tippy-top prior to take-off. Oil leaks *generally* develop over time; they don't immediately go from "no leak" to "full leak" although anything is possible. But for argument's sake, we'd have to assume that before the engine began consuming all oil and no fuel, the oil supply would have to have been drawn down somewhat. And once all of the oil was consumed, the engine would revert to running on fuel, albeit for a very short time.
I'm not disagreeing with Nick; his scenario is certainly plausible given the design of turbine engine FCU's and governors, and it's neat to speculate about such things from a theoretical aspect. It's just not something that we, as pilots, really need to dwell upon in a practical sense. Because if you develop such a massive internal oil leak as he described, there is no alternative: the engine is going to go BANG! very shortly for one reason or another.
(Oh, by the by, we keep talking about "seeing reduced oil pressure" as the oil runs out. Remember that in flight, the first thing you'll probably notice is that the torque gauge goes bonkers, as it is powered by oil pressure in the 206. On the ground, at idle it would be normal to see reduced oil pressure.)
Nick - I wonder why this sort of info isn't readily available??
I have been flying turbines for 34 years now, and this thread is the first time i have ever seen this information. A bit scary that "shutting down" the engine will have no effect and it will burst its breeches with a cloud of dust and a hearty "hi-ho Silver".
It should be taught in any turbine ground school. I have done the Allison school a couple of times and they didn't talk about a major internal leak at all.
I have been flying turbines for 34 years now, and this thread is the first time i have ever seen this information. A bit scary that "shutting down" the engine will have no effect and it will burst its breeches with a cloud of dust and a hearty "hi-ho Silver".
It should be taught in any turbine ground school. I have done the Allison school a couple of times and they didn't talk about a major internal leak at all.
A) It's not a problem to worry about; and
B) It doesn't happen.
Well, I take that back - we've all seen some massive internal oil leaks caused by bearing or seal failures. Happy Landing ! can attest to that. But Nick's theory is that an engine could develop an oil leak so bad that the flow of oil could exceed that of the fuel...and that the engine would happily run exclusively on that oil while the FC took a break and ran itself back to idle.
Umm... Well, maybe...if we had a humongous oil supply.
The RR/Allison 250-C20B in my aircraft consumes about 25 gallons of fuel per hour in cruise. This means that a tad over 1.6 quarts of fuel are being slurped every minute. If the engine should "suddenly" switch over and start using oil instead of fuel, how long do we think it would run before exhausting the oil supply? I'd be completely out of oil in under four minutes. How much oil does *your* system hold?
Trouble is, we wouldn't even be starting from 100% full, even if the tank was filled to the very tippy-top prior to take-off. Oil leaks *generally* develop over time; they don't immediately go from "no leak" to "full leak" although anything is possible. But for argument's sake, we'd have to assume that before the engine began consuming all oil and no fuel, the oil supply would have to have been drawn down somewhat. And once all of the oil was consumed, the engine would revert to running on fuel, albeit for a very short time.
I'm not disagreeing with Nick; his scenario is certainly plausible given the design of turbine engine FCU's and governors, and it's neat to speculate about such things from a theoretical aspect. It's just not something that we, as pilots, really need to dwell upon in a practical sense. Because if you develop such a massive internal oil leak as he described, there is no alternative: the engine is going to go BANG! very shortly for one reason or another.
(Oh, by the by, we keep talking about "seeing reduced oil pressure" as the oil runs out. Remember that in flight, the first thing you'll probably notice is that the torque gauge goes bonkers, as it is powered by oil pressure in the 206. On the ground, at idle it would be normal to see reduced oil pressure.)
I'd agree with that. My oil pressure went first on the above incident, but on another incident on a 206 where an oil line was not retightened properly following maintenance, it was the torque gauge that went bonkers (extremely erratic) long before the oil pressure started to drop, which it eventually did (over a bunch of trees again). I had an engine let go in a 206 following an engine overhaul as well, and it was the torque gauge that went erratic first, followed by the ol pressure, followed by a chip light, but I was on the ground by that time.