I suspect I have water in my static system

[PMcClure]

Where are the drains in an ovation? In New York today leaving this afternoon.

[Marauder]

Probably in the same spots as the rest of the fleet. Under the battery access door on the fuselage for the static port and the pitot drain is near the left wing root.

[carusoam]

On the O1, there are two static drains...

One under the tail, as usual...

The other, is under the leading edge, pilot side...

Good luck,

-a-

Or like Chris said above...

[jlunseth]

And they may be hard to see inside of small holes in the skin.  At least the one on the pilot side leading edge is.

[John Pleisse]

The static drain pump on a 201 is pilot underside aft of the cowling and infront of and just below the wing root. Stick your fingure on it and press several times, if applicable to the O.

[PMcClure]

Found the drains this morning and tried to drain the system Thank you!. But, there was no water. The problem started on descent  yesterday after a 3.5 hour flight. The VSI and Altimeter were jumpy (200-400 feet) and the A/P was oscillating pitch. I switched to Alternate Static source and the Altimeter read 200ft lower and the VSI about -200 fpm more (after a big jump). The A/P continued to pitch. I turned off the A/P and flew the approach no problem. Left VFR this morning and system worked well. But then again in descent after 3.5 hours, the same issue. Sure seems like water or some obstruction. Any thoughts?

[Marauder]

I'm not surprised by the alternate static air difference. It is the difference between static ports located on the sides of the plane and the alternate port location (usually in the plane).

 

It does sound like some kind of obstruction. What is the airspeed indicator doing during all of this?

[PMcClure]

Air speed was normal. Difference between alt and regular static air was initially very great then settled out to 200' to 400'. Only on descent makes it seem like it is moving with gravity.

[Marauder]

Air speed was normal. Difference between alt and regular static air was initially very great then settled out to 200' to 400'. Only on descent makes it seem like it is moving with gravity.

Sorry for taking so long to reply. The pitot and static systems are tied together. If you had a blockage in the static system, I would expect the airspeed indicator to be affected since airspeed is derived by the difference between pitot and static pressures. Since it is not, it complicates the problem. You didn't mention the make of the AP. My STEC uses a pressure transducer for altitude hold. This is connected to the static system. From the description of your problem, it sounds like it is plumbed the same way. If you have a static system leak that is intermittent, I could understand the variation in the VSI, altimeter and pitch hold. It would be the difference between static pressure at the source of the leak and the original static system (sort of like turning the alternate static port on and off intermittently). Another possibility is that one of the instruments could be leaking internally or a fitting could be loose on one of the instruments. This could also explain why the airspeed is not impacted or does not appear to be. It may be, but since the leak may only vary the airspeed a few knots and you are not noticing it. Also, someone can correct me on this, but I think your blind encoder (if you use one) is also connected to the static system. I would think your reported altitude would be bouncing around and may make ATC question your altitude. Another thing that could be happening is the O ring on the static drain is not sealing. Mine has been replaced routinely over the years either because my pitot static system test fails or my mechanic changes it out preventatively. Sounds like you may need to take it to a shop to have them look at it. Sorry I couldn't help more...

[carusoam]

Chris, well written dissertation on aviation plumbing...

P, the static system is made up of "clear" tubing. You may be able to see if there is water in the tail cone portion of the plumbing. There are two static ports back there as well... One on each side.

Best regards,

-a-

[PMcClure]

Thank you for all the info. I will check the plumbing this weekend then head back to the shop if needed.

 

Some more comments:  I just picked the plane up about 2 weeks ago from the Altimeter checks. Also an AI replaced. In the past three weeks, I have had several (maybe 3-4 in 25 hours XC) reminders of altitude from ATC, even though I was dead on. Finally, I checked the pressure altitude by setting the Altimeter to 29.92 and comparing to the transponder. They matched but not sure where the transponder gets it's altitude info. Also cross checked TAS with Garmin calculations and they are within 1-2 knots in level flight. A/P is a KFC 225.

 

The problem is only noticed on descent. Other than that, I cannot detect any problems. 

[Marauder]

Thank you for all the info. I will check the plumbing this weekend then head back to the shop if needed. Some more comments: I just picked the plane up about 2 weeks ago from the Altimeter checks. Also an AI replaced. In the past three weeks, I have had several (maybe 3-4 in 25 hours XC) reminders of altitude from ATC, even though I was dead on. Finally, I checked the pressure altitude by setting the Altimeter to 29.92 and comparing to the transponder. They matched but not sure where the transponder gets it's altitude info. Also cross checked TAS with Garmin calculations and they are within 1-2 knots in level flight. A/P is a KFC 225. The problem is only noticed on descent. Other than that, I cannot detect any problems.

You certainly have a mystery on your hands. With the work around the back of the panel, it is possible they moved or disrupted one of your static connections. What transponder do you have? You may have a blind encoder that sits in the avionics bay and is connected to your static system. If you are near your pitot static inspection time, you may want to just have them figure it out while doing the tests.

[PMcClure]

There is a question about water in the static system in AOPA magazine today (Quiz section). Sounds exactly like what I am experiencing, but they mention in a climb.  

 

PS - the Pitot/Static check was done at the same time as the Altimeter and AI. 

[201er]

I'm having the same issue but in the climb. Pressing the drains yields nothing. However, the other symptom I get is a displaced ASI on the ground. If I land, shut down, pressure changes, come back, ASI reads 20 knots sitting in no wind. Pulling ALT air seems to clear it out and allow it to resume normal function when returned to normal static.

[N601RX]

There may only be a small amount of water in the system that normally leaves it open, but in a nose up or down altitude it may be enough to block the tube.

[201er]

How do you get rid of it? Shouldn't it eventually evaporate out of the system eventually?

[PMcClure]

Well, I took off the inspection panels but didn't see any water. I am going to head back down to the shop next week just to have them check it out again. Thanks again for the help. I'll let you know if we find anything. 

[201er]

I was at the shop today. They ended up blowing water both out of the static and the pitot. Works good now. I'd say just preemptively have them blow it rather than diagnosing.

 

I was having problems on climb where it wouldn't let me retract the gear and I had to hit the overrirde! Definitely a pitot/static water issue.

[PMcClure]

OK - I have been thinking about this and it make sense that the fluctuations only happen on descent or climb. If water is in the system, the pressure diff would build up as the water blocked the static system. At a certain point the diff pressure would be enough to clear the system momentarily the close off again. So, the system would fluctuate as the pressure changes (air kinda bubbles or burps out). But then at level flight, the pressure would stabilize and would be "off" a certain amount. The A/P and altimeter would get the information from same source so the pilot would get different readings than ATC since the transponder reports pressure altitude (blind). Depending on where the water is would determine if the error was caused in climb or descent. 

 

Could really matter at minimums and possible you would never know you were off. Insidious error. Hope to get it fixed this week. Visual check showed no water in system and ground check shows correct altitude as it would since the blockage probably happened at ground level and error would only be temp if a minor amount of water. 

[201er]

I had a similar problem. You brought up IFR minimums which is the reason for the static check. But you know what's scary? My plane passed both pitot and static recently despite a similar clog. Water was not present in the drains either. Yet when I decided to have them blow out all the lines just in case both pitot and static had water.

[manu damaschin]

I had the same issue on a winter at FL140 at -35 celsius...and had no water on the static system. But the ALT worked well...

[M20S Driver]

N/A

[John Pleisse]

Pitot tube?

[M20S Driver]

Yes. 

 

Pitot tube?

Yes. It must be on Pitot tube side if any.

[jlunseth]

PS  The drain in the forward underside of the left wing is a pitot drain.  The drain on the underside of the fuselage aft of the wing is the static drain.