Bell Jetranger puff of smoke from exhaust during flight

[hyperflyboy]

Does anyone have any idea what caused this?
While coming to land, once a hover was established, a large puff of white colored smoke came out of both exhaust stacks.There were no indications that this happened.
It was only spotted after watching a video that was recording the landing.
After reviewing a video of the takeoff of the same flight, a small puff of black smoke (looked like carbon) was observed during the hover transition to takeoff. The flight was about 15 minutes long and another 15 minute flight that occurred after the smoke flight showed no smoke events.
Has any body seen this happen on JetRangers or other helicopters with RR250-c20s in them?

[Ascend Charlie]

Hueys would do this with great regularity.

Usually a buildup of oil that sneaks through a labyrinth seal and into the hot exhaust. An attitude change can move the pool of oil. C250 does it on shutdown too, into the right exhaust stack if my rattles brain is correct.

[haihio]

I have seen i happen sometimes on short final as the pilot pulls power both in our jet rangers b3s and in our as355's that also have the same engine.
I think it's normal for this kind of old engine technology.

[hyperflyboy]

Thanks Charlie

The smoke was from both stacks and I worry that if this is occurring regularly, the oil passing through the turbine section will eventually cause damage or failure of the turbine wheels due to thermal shock stresses. I don't know how often it happens. I have seen only a very small reduction in the oil levels over time. Should I be concerned? From what I understand, if the smoke was only from the right stack it would be directly from the engine transmission venting.

[hyperflyboy]

Halhio
I was adding a bit of power at the time. Could it be something to do with an FCU and governor over response pumping a quick burst of too much fuel? I don't know if that even is possible.
Ive read that a dirty fuel nozzle will cause an occasional burst of smoke in turbines but I don't know if this applies to rr250s. I'm hoping its not a recurring burst of oil leakage issue.

[wrench1]

Hyper:
If lucky, the oil check valve on right side of turbine is slow to react to your power changes. If unlucky, a turbine labyrinth seal is moving during power (air pressure) changes as AC mentioned above. It really shows after landing when you roll the throttle to idle and you make enough smoke to screen the entire Royal Navy. On windy days a pilot wouldn't even know until the fire brigade shows because a witness thought you were on fire. Check valve is easy (cheap) troubleshoot, but mostly lacks results since a "new" style check valve came out 20+ years ago. YMMV but most would hold off on a turbine change until it became a mosquito chaser on the ground. There are a couple other reasons but these are the top two on my list.
W1

[wrench1]

Hyper:
Here's some additional reading. Not for a C20 rather a C30 but they're all 250 series engines. RR main concern is with continuous smoking.
2793

[hyperflyboy]

wrench
Thanks for the info.
A local AME told me it could be something with the FCU adjustment. Does that make sense? Its got about 450 hours before timex.
I've never noticed smoke on shutdown or startup.

Hyper

[500guy]

wrench
Thanks for the info.
A local AME told me it could be something with the FCU adjustment. Does that make sense? Its got about 450 hours before timex.
I've never noticed smoke on shutdown or startup.

Hyper
I'm just a pilot , but....
If it is a leak in the lab seal you need to be mindful of coking and N2 lockup. Carbon on the turbine blades accumulates in the outer edge near the scatter shield and can contribute to wheel cracking. Also If you start getting N2 lockup its time to pull the turbine. On a 500 the rotors should be turning around 12-13% N1, before fuel is introduced. If it isn't, starts put way more stress on the #3 and #4 wheels (because they are stationary for the first few seconds in the flame path) and can eventually lead to failure. I've seen black smoke on 530s with C30s but never any smoke on a 500 with a C20.

Are you running HTS oil?

[parabellum]

Years ago we were told that occasional puffs of black smoke from the exhaust of the 206, (Allison), 205 (Garret) and WS55/3 (Gnome) was the turbine shedding a build up of carbon on the blades and was both healthy and desirable. Blue smoke, which I believe to be oil, would bother me.

[hyperflyboy]

Here are a couple of shots of the black puff of smoke that occurred. The left image is the initial burst and the right is a fraction of a second later. It looks like it is loaded with carbon. These shots are about 4 minutes after the first start of the day just after lifting off into a hover.
Hyper

[hyperflyboy]

500guy
I'm using Areoshell 560.

[FH1100 Pilot]

If you watch helicopters with turbine engines for a while, you'll notice that they all seem to emit a puff of black smoke now and then. It doesn't always seem to be associated with power changes. I've seen it so many times that it must be considered normal.

Blue smoke? I'd watch that oil consumption closely.

[Cyclic Hotline]

Coking in the combustion liner. It builds up, breaks loose and comes out as a puff of black smoke in the exhaust. You may see some evidence of this when you pull the combustion cover, and occasionally see some quite large build ups around the surround to the nozzle. Nothing to worry about, unless something else starts happening. Ive nevwr seen any damage from this - its a piece of real hot carbon going real fast through a real hot engine, followed by a nozzle and fast wheels.The comments on turbine lock up, carbon inspections in the sump, etc, are all important to watch, but not what you are seeing here. I've seen it in all variants of the C20 in every airframe.

[helicopterray]

The gearbox vent orifice isn't set up correctly. It's pressurizing your gearbox, which is causing oil to blow out the exhaust.
Change the vent orifice one size bigger, or drill it one size larger. Not you personally, but your AME.
It's located on the left side of the engine, above the PC filter.

[RVDT]

I would go with helicopterray's suggestion, the other stories here are mainly old wives tales rehashed.

There is a bit to be concerned about that the gearbox vent orifice is not "set up" correctly or has issues.

The vent controls the labyrinth seal airflow at the rear of the compressor.

To set it correctly the plug is drilled one drill size step at a time until it leaks oil and then you go back one size. The idea being that there is enough leakage of air to allow flow of oil through the bearing. If you do have a vent that is one size too big and some oil leaks out of the vent it is not such a big deal.

Where the problem lies is if the vent is too small and does not allow oil to flow through the rear compressor bearing (2) correctly and can actually blow the oil out of the bearing.

It might pay to check this as it could easily lead to bearing failure.

The large amounts of white smoke is NOT normal and your AMT should be able to find a reason for it.

[gulliBell]

I reckon. Not normal. Sure, I used to see Huey's do it regularly, but not from a 206. Pilot write it up.

[500guy]

Aeroshell 560 ins't specifically listed in the C20 operation and maintenance manual. (Areoshell 500 and 555 are) does it meet the STD or HTS Milspec?

[bob2s]

Cause of white smoke on shut down.Look in exhaust on daily insp. and if oil is found in bottom of exhaust collector then the
Number 5 bearing bellow oil seal will need to be looked at

[Saint Jack]

There used to be a practice of walking the rotors of a 206 backwards for three revolutions immediately after shut-down although you don't seem to see it much these days. The intent was to turn the N2 turbine (turning backwards engages the freewheel and turns the engine) and rub any accumulated carbon build-up, particularly from the No. 6 and 7 bearing labyrinth seals. Try it and see if it makes any appreciable difference to your smoking problem. Don't bother with the gearbox vent orifice at this stage - it's too early. Nor is the problem likely to be the oil check valve, this has an entirely different purpose. FCU settings - umm, not likely. BUT, one thing you may consider is changing your oil, although I've no experience of AeroShell 560, I can assure you that Aeroshell 500 and 250 series engines make to very worst of bedfellows. I speak from experience, using Aeroshell 500 in a 250 Series engine just about guarantees excessive carbon build-up. My suggestion is go to Mobil Jet Oil II. Let us know how what happens.

[hyperflyboy]

Any chance the white puff of smoke may be from a partial compressor stall? Power was low then bumping it up a bit rather then raising it slowly. If you watch the video you can hear a slight pop as the smoke puffs out.
Not noticed in the cabin though.

I found this youtube video of a BK117 helicopters engine doing something similar.
[https://www.youtube.com/watch?v=H7DIAnz40dc]

H7DIAnz40dc

[Saint Jack]

A compressor stall, even a partial stall in a single engine helicopter like the 206 Series, will produce a slight-to-noticeable torsional oscillation (yawing of the entire airframe about the mast) as the engine power to the transmission fluctuates. Also, the instrumentation will similarly fluctuate to indicate the event, particularly the N1 Indicator and Torquemeter - did you feel and/or observe anything like this? If not, it was probably your imagination.
A few questions at this point, a) Are the rotors being turned backwards for three revolutions after each shut-down as I described earlier? b) Are you and all others flying this helicopter observing the two-minute dwell time between rolling back to flight idle and shut-down?
I'd like to revisited the "FCU settings" for a moment. with the twist grip full open, does the lever on the FCU make FIRM contact with the full open stop? This is very important and is the reason why you see that very powerful-looking spring around the lever spindle. Get a piece of very thin paper and place it on the full open stop, then gently roll the twist grip to full open to trap the paper. Without touching the twist grip or the FCU arm, gently try to pull the paper away, if it tears everything is OK, if it pulls away the N1 controls need re-rigging.
Finally, can you say that all engine maintenance requirements have been perform conscientiously, I'm thinking of the No. 6 and 7 oil jet inspection, the No. 6 and 7 scavenge strut cleaning and fuel nozzle cleaning plus a spray pattern check, etc.

[Jetscream 32]

@hyperflyboy
I think you are one puff away from a much larger issue - your smoke issues are not normal and certainly not with such regularity. The black puff on start up is the cold ejection and the white is the same problem when hot, what you don't know is how often its doing the same en-route, I would put money on this doing it every "x" minutes, which is systematic of a tiny problem, that will eventually turn into a much bigger problem. Hangar time me thinks and be on your toes for auto at the whiff of a problem till you get it under cover and the cowlings off!

[SuperF]

Interesting what Saint Jack said. I had never seen any helicopter oil in NZ for at least 30 years other than Jet II. now there is the new 256 or what ever it is, and other people go and buy some other different oil, probably cheaper...

But there must be a reason why, right through the 80s and 90s most people, that were running JRs and 500s, all had Jet II. it certainly wasn't the cheapest, but all i got told was the other stuff was ****!

[John Eacott]

I used Aeroshell 560 from the late 1990's on, in both my 206s and my BK: third generation low coking and met the specs for the JetRangers. Coking issues on the LTS101 led me to that choice with expert advice, it improved the oil galleries in the LTS 101s and was far cleaner at oil changes in the 206s than Jet II ever was.

The 'puff' of smoke in one of the photos is far more than a puff, IMO, and is white not black. Agree that is could be indicative of something more serious.

[206 jock]

Cause of white smoke on shut down.Look in exhaust on daily insp. and if oil is found in bottom of exhaust collector then the
Number 5 bearing bellow oil seal will need to be looked at

I had this issue on my 206A/B C20: on shutdown it would puff out a plume of smoke.

[ericferret]

In the early 80's Hughes 500D's were delivered with Mobil Jet II. In the UK AS 500 was much used and easy to obtain. We noticed that aircraft that were changed to AS500 had much higher levels of carbon forming in the oil. One of the aircraft had a turbine seize due to blocked oilways and all owners were advised to change back to Jet II.
The levels of carbon soon reduced to normal.

Around this time we also had AS555 which may have had better coking characteristics
but ate helicopter gearbox seals for breakfast.

Bond helicopters had massive coking problems with the Allison C30 in the S76. The problem was so bad that Sikorsky brought out a mod to armour plate the tail rotor drive shaft (20 kilos of steel) just in case the turbine bearings seized and the turbines departed. Bond were stripping and cleaning out a pair of turbines every weekend, in effect a six week cycle as they had six aircraft, in an attempt to alleviate the problem.
They ran a comparison test with each aircraft on a different engine oil, AS 500 was junked and Mobil 254 was found to give the best results. This was still the standard UK engine oil (used in the Arriel) for the company now CHC more than thirty years later.
Replaced with BP2380 for the PT6.

[hyperflyboy]

I'm the only one flying this machine at this time and it flies once every week or two for about an hour. The blades are rotated 2.5 turns counter-clockwise every start and shutdown with a 2 minute cool down every shutdown as well. Annual inspection was done about 20 hours ago with a compressor wash and the usual engine and airframe maintenance all done by a reputable maintenance shop with 30+ years experience with 206's.. The engine has a monitoring system that prevents hot starts and records all exceedances and maximum engine and air frame parameters all of which appear normal.

I just checked the FCU lever position to see if it contacts the stop at full open and it does not. There is about a 0.100" gap.

[chopjock]

hyper
The blades are rotated 2.5 turns counter-clockwise every start and shutdown

Surely they should be rotated CLOCKWISE,(Backwards) in order to rotate the power turbine and crack any congealed oil on the bearings etc?

[hyperflyboy]

My mistake, it is clockwise looking down from above. I turn the blades backwards so the free wheeling clutch is engaged.

[PabloLAFDmech]

hyper


Surely they should be rotated CLOCKWISE,(Backwards) in order to rotate the power turbine and crack any congealed oil on the bearings etc?

The carbon is built up on the labrynth seals in the turbine , extreme buildup can cause damage to the turbine and lockup.

[RVDT]

hyperflyboy,

Just looked at your photo - not good.

Reasons why -

1/ The full throttle stop determines your MAX N1 speed. Possibly not an issue at the altitudes you are flying at.
At higher density altitudes you will not achieve MAX N1 and the engine will TOP and the RRPM will decrease before you reach TO power.
If it was a multi-engine install - an even bigger issue as your remaining engine will not achieve OEI power.

2/ The lever will possibly be under the 30? degree point when at IDLE and too close to ICO (idle cut off). The downside of this is that should you do a practice power failure there is every chance it might flame out and make it a little more interesting than it needs to be!!

With the engine shut down - Fuel OFF - BP off - Check the throttle as follows -

CLOSED it should be preloaded against the stop on the FCU - if not you can have afterfires.

Open the throttle slowly until the stop just clicks out on the twist grip - pointer on FCU should NOT be under the IDLE marking.

Open the throttle fully and it should be preloaded against the MAX N1 stop.

Close the throttle slowly to the twist grip idle stop - again the pointer should be above the idle mark.
If the difference between opening and closing is significant your throttle linkages are worn out.

The IDLE position of the lever does not relate to the IDLE speed - that is set within the FCU although can be cheated with bad rigging.

To check the actual IDLE speed within the FCU - on shutdown - slowly decrease the throttle after pushing the IDLE stop and watch the N1 tach. Note the RPM where the fuel shuts off.
If lower than the recommended IDLE RPM get it adjusted.

Frankly I am surprised that your shop has let this slip as it is pretty important yet basic stuff. I would be a little apprehensive as to the rest of your problems when you have an obvious issue such as this!

[Saint Jack]

Amazing isn't it, I went to see the doctor with a cough and a runny nose and spent the next four and a half days in hospital! Anyway, back to the matter in hand, RVDT has essentially put in writing what I was thinking. the final paragraph of his post above (#32) is the conclusion I was coming too also. I'm sorry hyperflyboy, but your statement in Post #28 that "engine and airframe maintenance all done by a reputable maintenance shop with 30+ years experience with 206's" is not supported by what you're experiencing which, quite frankly, are relatively straightforward problems for an experienced 206/250 mechanic/engineer to diagnose and rectify. Do you have any alternatives for maintenance support?

[Sir Korsky]

Not the papal copter is it?