Pitot Static Failure - help?

[201Steve]

Hello friends,

I just had my first experience with a pitot static failure. For the first time since I’ve owned my ‘77 J, I was forced to leave it outside. :( Had a little bit of rain, etc and it hung out on the ramp for 3 days. Hopped in to take off, airspeed came alive and kind of stuck at 55knots next thing I knew I was airborne so after cleaning up the airplane and keeping a shallow climb rate to build speed, it only climbed to about 68 - 70 knots. After confirming gear was up, flaps were up, I went to GPS ground speed which read about 115 knots so felt comfortable that it was indeed not reading correctly on IAS. Climb rate was showing crazy and altitude also acting erratic.  Long story short, I went to alternate static and everything stabilized. Where do I start to trouble shoot? I did not see any obvious obstructions to pitot or static port, but it seems to me like there is blockage somewhere. Thanks for any feedback

[MIm20c]

Water in the line back in the tail area?  There should be a drain at the low spot. 

[201er]

Did you drain the pitot and the static on your preflight? Did you use a pitot cover?

[EricJ]

There are two pitot-static drains, one under the leading edge of the wing root on the pilot's side, and one back toward the static ports under the trailing edge of the pilot's side wing root.   Open each to see if there's any water in the system.   

 

[PT20J]

4 minutes ago, EricJ said:

There are two pitot-static drains, one under the leading edge of the wing root on the pilot's side, and one back toward the static ports under the trailing edge of the pilot's side wing root.   Open each to see if there's any water in the system.   

 

Well, actually, the wing drain is for the pitot, and the tail drain is for the static line. Since the pitot line only goes to the airspeed indicator, symptoms don’t point to a problem there. Nonetheless, it’s good to  check them both during preflight.

Skip

[carusoam]

So the alt static valve improved things...

That means something blocking the static system operation is the first place to check...

Does any water come out of the static drain?

Static lines are often clear plastic... they are easy to find in the tail... they initially go between the two static ports...

Start there...

Use caution if any ideas come to mind... compressed air carries too much force and can damage sensitive instruments...

Expect water to be the most likely cause... See if you can find it.

Other challenges found by MSers... are leaks and cabin pressure related....

PP thoughts only, not a mechanic...

Best regards,

-a-

[201Steve]

@carusoam you da man! Water built up about 2” in front of the drain valve

Edited August 5, 2019 by 201Steve

[kmyfm20s]

As mention above, Pitot cover and drain the lines on preflight. Some people put static port covers on. The only time I got ever got water in mine was when the detailer pressure washed my static port thoroughly. The rain must have had the perfect angle on your ports. Always drain on preflight.

[EricJ]

It may be a one-time thing, you never know.   At least now you know where the drains are and where to look in the tail for a spot check.

The main issue with static port covers is that people forget to take them off, and they're usually not needed.

I'd just keep an eye on it and check it carefully the next time it's out in the rain.  If it does recur it may be worth checking if there's an unusual leak or something that is collecting water where it shouldn't.  The more common problem to have after sitting in the rain is water in the fuel tank, so you just got a different one. 

 

 

[carusoam]

It takes quite a special rain storm to load water into the static system...

@201er actually captured some video of the effects, and the draining of the system...

When the conditions of the rain is right... there can be quite a bit that gets into the tubes...

Did you see heavy rain and high winds at all?

Best regards,

-a-