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Its Cold at 25,000 ft


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I am a new (August 2019) Bravo owner and Im in love with her!!!  Ive flown her almost 100 hrs since.  I have a few questions about a recent flight I had and what I experienced.  I was flying from Boise Idaho to Kansas city.  My flight plan was to go to 19K to take advantage of a tail wind and to get over some clouds which were solidly in the freezing level.  As luck would have it the clouds , of course, were higher than 19 so I kept climbing to 25000.   The oat ended up at -35 F and that's where a few curious things began to happen.  One my fuel pressure slowly increased to over 62 and my oil pressure decreased to below 50.  Can anybody explain why.  I have a couple of ideas but interested in hearing from the group.  I actually had to run through a few clouds and I felt. ok because the temps were so cold I didn't thing ice would form.  I was correct but I have a question.  My Mooney is equipped with TKS, so naturally I turned it on but the odd thing was that a very few Ice "clumps" formed and slid back on the wing ONLY where the tsk fluid was.  The TKS fluid is new and would not have any water in it it was right out of a new barrel.  The parts of the wings behind the landing lights were COMPLETELY free of any ice. I am wondering if anyone else has experienced this.  Finally I noticed at altitude and super cold the fuel tank selector switch became hard to turn.  (related to fuel pressure and the increased viscosity of cold fuel?)

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I don't have any direct answers to your questions, but here are a couple things I'll comment on. Back in 1996 I bought a Bravo and for the next 3-4 years routinely went to FL250 without any backup plan if my Oxygen system failed. I am much more cautious now. I always have a portable tank easy to get to. Useful consciousness is not much more than 30 seconds at FL250 so most of the time flying in the teens works out just fine for me. I also set my altitude pre-select at a breathable altitude with an aggressive descent rate so all I have to do is engage that if something went wrong. Also having a CO detector is a must, especially when using cabin heat.

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I’d guess the oil pressure lapse is related to outside air pressure.  If SL is 14psi and 25,000 is 5.5, the oil pump is raising the pressure from a lower static pressure in the sump.

same reasoning explains the lower IAS limit for FIKI TKS at altitude.  There’s only so much work the pump can do.

Guess on the tks ice? There was some water in the panels or tubes.  It can happen if the plane is outside in the rain.

-dan

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I haven't seen such pressure readings, but I don't go above 18K since I don't have a mask, only the cannula. 

The TKS sounds like you had trace icing and just couldn't really see it..   Ice can form in a wide temperature band.. The liquid in the clouds doesn't need to be at the same temperature as the air, it can be rising or falling or supercooled  -35C is still not out of possibility for icing. 
https://www.eoas.ubc.ca/courses/atsc113/flying/met_concepts/03-met_concepts/03g-Icing/index.html

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38 minutes ago, LANCECASPER said:

I don't have any direct answers to your questions, but here are a couple things I'll comment on. Back in 1996 I bought a Bravo and for the next 3-4 years routinely went to FL250 without any backup plan if my Oxygen system failed. I am much more cautious now. I always have a portable tank easy to get to. Useful consciousness is not much more than 30 seconds at FL250 so most of the time flying in the teens works out just fine for me. I also set my altitude pre-select at a breathable altitude with an aggressive descent so all I've have to do is engage that if something went wrong. Also having a CO detector is a must, especially when using cabin heat.

I agree with you about flying in the upper end of the service ceiling. 30 seconds is not much time and by the time know you have a problem chances are it’s too late. I have done it a couple times but don’t think it’s a great idea in aircraft like ours.

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welcome aboard Dave!


Which moisture absorber did you use for the fuel? Something like this? https://www.skygeek.com/prist-44637-hi-flash-hi-flow-anti-icing-additive-5-gal.html?utm_source=googlebase&utm_medium=shoppingengine&utm_content=prist-44637-hi-flash-hi-flow-anti-icing-additive-5-gal&utm_campaign=froogle&gclid=CjwKCAiAnfjyBRBxEiwA-EECLPbdPNw6-bNeQToXi_wRgtc6YDHaWYuYI-qMudGTWWEaxfGTfmtfVBoCMM4QAvD_BwE

The Mooney POH has a list of different chemicals that are OK to use... and procedures that go with that...

At -35°F you have entered an area that most people don’t fly GA airplanes...

So... discussions on equilibrium quantities of water dissolved in the fuel don’t come up very often...

As temperatures get that cold... the small amount of water can drop out of solution, or just freeze in odd places...


As a new member of MS...

Maintain a thick skin going forwards as some people will be trying to offer you some good advice... it just might not sound so nice... :)

Expect to see topics of...

  • Back-up O2 systems
  • O2 measuring devices...
  • CO sensors
  • TKS maintenance and pre-flight activities...
  • PPI... pre-purchase inspection...
  • TT... Transition Training...
  • Pressure gauges that are PSIG.... vs.  PSI. (One takes into account the outside pressure variation, and one doesn’t, which doesnt’ usually affect the rest of the fleet...)

Flying above 20k’ comes with lots of additional challenges...

Preparation is everything...

And of course we/MS have lost a Mooney because their Osystem failed at altitude... while on the way to an aviation safety presentation.

Hope we get to know you better... tell us about yourself and your experience... :)

Why did it take so long to join MS?

Welcome aboard and best regards,

-a-

 

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If fuel pressure sensor is a diaphragm type, then it would measure the difference in pressure in ambient pressure and fuel pressure, so that will result in higher pressure readings.

What was the oil temperature? Higher temperatures result in lower oil pressure, that is why you can high oil pressure on takeoff.

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Welcome aboard, Dave!

I hope you enjoy your Bravo as much as I enjoy mine.

Comments:

  • Time of useful consciousness at 25,000 feet is 3 to 5 minutes -- assuming you are in good health and no rapid decompression (hard to get in a Bravo) which reduces TUC.
  • If you experience an oxygen system failure, descend IMMEDIATELY. Do not ask permission, advise ATC as you begin the descent. We lost a TBM-930 a few years ago because the pilot stayed at FL250 waiting for permission to descend after a pressurization failure.
  • The airspeed envelope for TKS is to ensure proper fluid coverage.
  • A thorough review of the TKS flight manual supplement is a MUST to safely operate in icing conditions. It includes important limitations and procedures. TKS operation is far more involved than flipping the switch when you see ice. The supplement includes a pre-flight inspection procedure that fully tests the system. As part of the pre-flight, TKS must be primed on the ground when ice expected. From the STC supplement: "Check evidence of fluid along length of all panels."
  • I run the TKS pre-flight procedure monthly (and for flight into ice) and clean the panels. TKS fluid is one of the approved cleaning agents that is conveniently delivered to the panels by the pre-flight test.
  • Review AC 91-74B regarding flight in icing conditions: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-74B.pdf
  • Review AC 61-100B regarding high altitude operations. The AC is written for operations above FL250, but it contains information useful to our operations at and below FL250: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_61-107B.pdf
  • It is always freezing at altitude so any visible moisture means potential ice.
  • I have noticed the reduction of oil pressure at altitude, but never really considered it as the pressure stays within limits.
  • It is very easy to exceed Lycoming's cooling limitation (50 degrees Fahrenheit per minute) operating in very cold temperatures. Be careful with power reductions and step to the CLD value on the JPI when descending.

Tailwinds,

David

 

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Thank you all for your suggestions and comments  that's really helpful.  I do have backup O2, set the MEA into my G500 and monitor my pulse ox and CO continuously.  Learned a long time ago in the Army to follow the P.A.C.E  acronym when dealing with high risk situations that require a plan if all goes to hell. (Primary, Alternate, Contingent, Emergent).  I go over the Rockies a lot so I need to be at 20 and 21 for my personal safety margin but I come down to the teens as soon as I'm over the highest parts of the trip. 

I do preflight my TKS usually once a month or so and don't mind letting the fluid come out all over the ramp to make sure every inch is weeping fluid. 

I just found it really curious the only trace ice on the airframe was where the TKS fluid was.  The Spot on the wing behind the landing lights (no TKS strip there) was clean as a whistle.  I know that TKS fluid has some water in it according to the manufacture.  This made me believe that at -35F the small amount of water was clumping on the wing.  It slid off and was not building up.  I think Next time im that cold and in clear air I'm gonna see if it happens again.

 


Some one asked about oil temp  at 25000 oat -35F 75% power and 125 rich of peak oil temp was 185  hottest cht was 360, TIT 1550.  IT was just really interesting to see the response of the systems to really cold really high flight .  Needless to say It is not my plan to routinely travel that high or that cold.

 

 

 

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I also now believe that the difficulty turning the fuel tank selector and the climbing fuel pressure was likely due to ice crystals in the fuel.  Lesson learned fuel additive in the winter just in case but I likely wont be flying up that high or that cold again. 

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I've been at FL250 and even 260 more than a few times in my 252. But without TKS, I've not done this in the winter. 

Useful consciousness is relatively short at those altitudes, but varies for different people. It's valuable to know how you personally are affected by the thin air. As others have said, take all the precautions. PulseOx, backup O2, Autopilot armed with lower altitude, etc. 

I personally love flying my Mooney in the Flight Levels. It really feels at home up there, and I typically have the airspace 10,000 above and 10,000 below, all to myself.

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2 hours ago, DaveMC said:

I do preflight my TKS usually once a month or so and don't mind letting the fluid come out all over the ramp to make sure every inch is weeping fluid. 

[...]

I think Next time im that cold and in clear air I'm gonna see if it happens again.

I have read that some animals have a taste for TKS -- bad for them. Not sure if this is true, but I dilute the TKS on the ramp with water when I am finished with a test. This also speeds evaporation of the fluid.

From the AFM supplement: "The TKS liquid ice protection system should not normally be activated in dry, cold air. The ice protection fluid is designed to mix with water impinging on the aircraft surface in normal operation. If dispensed in dry, cold air, the fluid becomes a gel that takes considerable time to clear, particularly from the wind shield."

Here is the M20M TKS FIKI supplement for your reading pleasure: https://www.dropbox.com/s/gslaobg3fbm60y4/M20M TKS FIKI Supplement.pdf?dl=0

Cheers

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38 minutes ago, David Medders said:

Guess that was one of those high pressure days where FL260 is below the 25,000 foot MSL limitation. (wink, wink)

No, my 252 doesn't have the 25,000 ceiling that your Bravo does. The M20K 252 is certified to FL280 :D

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3 hours ago, DaveMC said:

Thank you all for your suggestions and comments  that's really helpful.  I do have backup O2, set the MEA into my G500 and monitor my pulse ox and CO continuously.  Learned a long time ago in the Army to follow the P.A.C.E  acronym when dealing with high risk situations that require a plan if all goes to hell. (Primary, Alternate, Contingent, Emergent).  I go over the Rockies a lot so I need to be at 20 and 21 for my personal safety margin but I come down to the teens as soon as I'm over the highest parts of the trip. 

I do preflight my TKS usually once a month or so and don't mind letting the fluid come out all over the ramp to make sure every inch is weeping fluid. 

I just found it really curious the only trace ice on the airframe was where the TKS fluid was.  The Spot on the wing behind the landing lights (no TKS strip there) was clean as a whistle.  I know that TKS fluid has some water in it according to the manufacture.  This made me believe that at -35F the small amount of water was clumping on the wing.  It slid off and was not building up.  I think Next time im that cold and in clear air I'm gonna see if it happens again.

 


Some one asked about oil temp  at 25000 oat -35F 75% power and 125 rich of peak oil temp was 185  hottest cht was 360, TIT 1550.  IT was just really interesting to see the response of the systems to really cold really high flight .  Needless to say It is not my plan to routinely travel that high or that cold.

 

 

 

Looks like some really good numbers, I can’t get my oil temp below 200 over the mid teens.  What GPH were you running around and what power settings?  I know you said % horsepower but what MP/RPM?

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I know this isn't super relevant to the Bravos as it's a completely different engine than the 252's. But here's an example of engine parameters at FL230. The 252 is just really well suited to operate in the FlightLevels.

F0E84072-8802-495E-8312-B0B5CBF0ADE9.thumb.jpeg.8a7dbf97930f19716565fd2003e66e26.jpeg

 

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4 hours ago, DaveMC said:

The Spot on the wing behind the landing lights (no TKS strip there) was clean as a whistle.

Do you have LED lamps or the original halogens? and were they turned on?   the original lights were enough to heat the plastic and keep ice off that way.   LEDs don't have that power.   If the icing was very light, it would remain at the leading edge of the wing, and not slide off without the TKS fluid pushing it off of the edge. 

TKS fluid is ethyl alcohol and ethylene glycol.  So the glycol is poisonous to dogs, people etc..   Killfrost developed an eco version with propylene glycol, but there wasn't enough interest to get it approved.   The listed freeze point is -60C

https://www.aircraftspruce.com/catalog/pdf/killfrost MSDS.pdf

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While I don’t recall a similar Mooney TKS limitation, the Cirrus SR composite wing  has a minimum TKS operating temperature of -30F/ -34C despite a TKS reported freezing point of -76F/-60C. A Cirrus instructor and student found out that TKS inappropriately used below the limitation can lead to a freezing gel like mess on the wings as was discussed in a Pilots of America 2017 thread (2 Photos from that thread below):

97EC289F-9F33-45B1-B07C-2CBD7E0F334C.png

C4C721D6-6BBD-4D3B-9402-52D5B453FE9B.png

Edited by HXG
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2 hours ago, Davidv said:

Looks like some really good numbers, I can’t get my oil temp below 200 over the mid teens.  What GPH were you running around and what power settings?  I know you said % horsepower but what MP/RPM?

I lied I was at 80% 130IAS 192 True OAT -35 F 25000 ft  27.5/2400  FF 21GPM

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1 hour ago, PaulM said:

Do you have LED lamps or the original halogens? and were they turned on?   the original lights were enough to heat the plastic and keep ice off that way.   LEDs don't have that power.   If the icing was very light, it would remain at the leading edge of the wing, and not slide off without the TKS fluid pushing it off of the edge. 

TKS fluid is ethyl alcohol and ethylene glycol.  So the glycol is poisonous to dogs, people etc..   Killfrost developed an eco version with propylene glycol, but there wasn't enough interest to get it approved.   The listed freeze point is -60C

https://www.aircraftspruce.com/catalog/pdf/killfrost MSDS.pdf

The landing light were not on.  IT was the middle of the day so my visibility was really good and that area on both wings was clean

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1 hour ago, HXG said:

While I don’t recall a similar Mooney TKS limitation, the Cirrus SR composite wing  has a minimum TKS operating temperature of -30F/ -34C despite a TKS reported freezing point of -76F/-60C. A Cirrus instructor and student found out that TKS inappropriately used below the limitation can lead to a freezing gel like mess on the wings as was discussed in a Pilots of America 2017 thread (2 Photos from that thread below):

97EC289F-9F33-45B1-B07C-2CBD7E0F334C.png

C4C721D6-6BBD-4D3B-9402-52D5B453FE9B.png

Well that what I suspect happened  OAT was -35 F.  Good Lesson

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2 minutes ago, DaveMC said:

I lied I was at 80% 130IAS 192 True OAT -35 F 25000 ft  27.5/2400  FF 21GPM

Woah 21 gallons per minute - hope you have the Monroy's!! I know what you meant, just poking fun :) 

This fuel flow and power setting explains the better temps you were seeing but the TAS does seem a little on the low side... Maybe some of that junk on the wings was slowing you down.

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