JT15D-5D

MNSUpilot

Well-Known Member
Hey all,

Had an interesting 'issue' in our Citation Ultra today. I'll do my best to put out all the details to provide a decent picture of what was going on. Talked to a few people in the last couple hours and have heard the possibility of a bearing going bad more than once. Thoughts?

---

The first indication of anything abnormal was on the leg from BJC - EGE. We were at FL200 in moderate icing, at 180kias (~75%N1), all anti-ice on with lights out. We got a low groaning sound, from what I thought was the right engine, that stayed constant at a given power setting or would grow louder or disappear with small power changes. A few minutes later we got the descent into EGE and never heard another sound on the way in. Our only assumption was a bit of ice on a fan blade that was pronounced at higher RPMs. We checked on the ground and found no sign of ice or ingestion of anything in front of or on the fan itself of either engine. Both fans spun freely on the ground at EGE with nothing abnormal. (temps well above freezing)

We left EGE enroute to home with nothing abnormal on the takeoff roll with an N1 setting of right around 96%. We climbed through a little visible moisture starting at FL210 with the initial temp of -12*C with anti-ice on and lights out. Captain and I both started to notice what felt like an engine vibration. It wasn't violent, but enough to be uncomfortable and noticeable. I believe our climb power stayed in the 96-97%N1 area until we began pulling it back to reduce the vibration. A passenger did come up and ask what it was coming from and described it as a flutter-type feeling from the back. We kept reducing power to eliminate the vibration and it ended up disappearing at 89%N1. Due to the reduced power, we leveled off at FL370 at kept the power at 89% for quite awhile. We came up with the following numbers at FL370 with a temperature of -37*C while in an effort to increase power to climb up to FL390, although we ultimately stayed at FL370. Power was increased to 97%N1 initially with no vibration noticed but a large difference in ITT, with oil pressure and temperature staying the same.

97%N1 ITTs
Left Engine- 660 / Right Engine- 580-590

Power was reduced to 95%N1 and we recorded the following numbers:

95%N1
ITT -- Left Engine- 630-640 / Right Engine- 580
Oil Press -- Right- 84 / Left- 84
Oil Temp -- Right- 73 / Left- 67
Fuel Flow -- Right- 640 / Left- 620


We cycled the engine anti-ice switches and got the expected ITT rise equally on both engines. The right engine ITT always seemed to increase or decrease a fraction of the amount compared to the left engine with power changes with the thrust levers.

Thanks for the help!
 
The only time I've experienced something like a groan, it was hit or miss for several flight hours before we had a had a generator failure.

This was on a TFE-731, but I presume the symptoms would be similar on any smallish turbofan.
Sent from my DROID RAZR
 
Way outside my area of expertise since my turbine experience is way limited and my jet experience is nil, but wouldn't a conversation with your DOM and a review of the trend monitoring data (you do do some sort of trend monitoring, right?), possibly followed by a SOAP/filter check help get things figured out?
 
First off, yes we do trend monitoring data. I'm pretty darn new to all this so I figured i'd but a brief but detailed description and see what ideas get thrown around. Obviously with an issue like this we've been in contact with the DOM and the airplane was in mx today fixing a few other minor squawks from the flight and doing some troubleshooting on the engine issue. With that being said, the trend data is all normal in regards to power settings and temps across the board.

I don't recall the N2 numbers off the top of my head but we wrote them down and handed it off to the DOM. He was intrigued at the mention of a bearing going out, said they were going to check nozzles and maybe into the hot section today if needed. They were digging into it when I left.

The only other thing I noticed I left out was with the initial groaning sound on the first leg we did notice a different smell that came through the cabin. The airplane just got new interior put in so anything other than fresh glue throws up a red flag. It was NOT a burning smell or oil, it's tough to even put an exact description to it. I'd say the closest comparison would just be something that has been 'hot' like a shutdown engine, but once again, not a burning smell. Will continue to update as I hear more. Thanks!
 
First off, yes we do trend monitoring data. I'm pretty darn new to all this so I figured i'd but a brief but detailed description and see what ideas get thrown around. Obviously with an issue like this we've been in contact with the DOM and the airplane was in mx today fixing a few other minor squawks from the flight and doing some troubleshooting on the engine issue. With that being said, the trend data is all normal in regards to power settings and temps across the board.
So those numbers you posted in the first post, including the EGT split between motors, were consistent with the existing trend data?
 
Is it possible it was the pressurization system? I have noticed a tendency for some systems to clog with ice under particular circumstances causing a mild buffet sound and vibration. When you pull the power back you reduce the bleed air output and therefore change the pressure and airflow slightly within the system causing the buffet and vibration to change or cease. Just a random thought from a guy who has never flown a Citation.

Also, I would not suspect that a "bearing" within the engine would last more than a few seconds if it started to go. I could be wrong, but things are just spinning too fast and at too high of temperatures to allow things like bearings to fail slowly.
 
As some one else mentioned before there TFE-731 will do that when a a gen is failing. We thought we had one of those again a while back. It turned out to be a front fan out of balance. We had to have a guy come out with the special machine to get it back in balance. Similar symptoms that you are having and it was intermittent. It was on a Lear 45 for reference.
 
Here is a trend from a trip I did last night in an Ultra:

Left / Right (OAT = -22, IAS = 250, FL 340)
N1% 96.4 / 96.4
ITT 600 / 600
N2% 90.8 / 90.6
FF 700 / 700
OT 80 / 80
OP 78 / 75

It's not apples to apples but worth the reference. All of this said, I'm with the generator going bad crowd. I've lost 3 in the past few years.

Very interested to see what your maintenance department finds out.
 
So those numbers you posted in the first post, including the EGT split between motors, were consistent with the existing trend data?

Sorry I didn't specify. All the trend data was consistent up to this flight. Everything on this flight was right on except ITTs.

Got as much of an answer as I think we'll get until it flies again. Kind of funny. The moderate to severe turbulence over the Rockies caused the right gear door to drop a few inches and built up ice which the DOM thought gave a good explanation for the vibration, and lack thereof on takeoff and climb out.

I think they messed with the stator vanes and found the BOV was getting sticky on the right engine so that may explain the ITT differences. Going to TEB next week and will report back after that.
 
Sorry I didn't specify. All the trend data was consistent up to this flight. Everything on this flight was right on except ITTs.

Got as much of an answer as I think we'll get until it flies again. Kind of funny. The moderate to severe turbulence over the Rockies caused the right gear door to drop a few inches and built up ice which the DOM thought gave a good explanation for the vibration, and lack thereof on takeoff and climb out.

I think they messed with the stator vanes and found the BOV was getting sticky on the right engine so that may explain the ITT differences. Going to TEB next week and will report back after that.
Good luck. Like I said way out of my depth so I'm hoping to maybe learn a thing or two from your odyssey here.
 
Back
Top