Garmin airspeed reading 20kts while stopped on the ramp.

[warrenehc]

Hello all, 

I just got my plane back from the avionics shop with G3X and G5 upgraded. When stopped on ramp the IAS shows 20kt while stopped on the ramp. I have seen treads on the internet about this but for some reason I cannot locate them. 
 

Any help would be greatly appreciated.

Thank you.

[varlajo]

Likely static system blockage. Could be water, could be a bug.. 

[warrenehc]

Ok thank you in flight thing seemed ok but on ramp at idel it showed 20k.

[Jake@BevanAviation]

We had this happen before.  Turned out to be the GSU25 had a issue.  

[warrenehc]

With engine off it shows 0 TAS, with the slightest wind around the pitot tube (blowing air near it) causes it to jump. So it seems like it’s prop wash getting over and manipulating the TAS on the ground stopped. Different from last Mooney with Dual G5’s. I didn’t have that happen.

[201Steve]

They probably left it outside after they got finished and water got inside your static port. Sometimes the drain valve underneath the tail will clear it, sometimes it’s not enough to drain out and you have to pull the battery panel and visually locate and disconnect the line to let water trickle out. 

[PT20J]

If it's pitot/static related, it should affect both the G3X and G5. If it's moisture you could try pushing both pitot and static drains.

[DC_Brasil]

My M20J with a G3X and G5 has a similar albeit not identical behavior: with engine running but at idle it will show zero IAS. However, at runnup power it will register a prop wash at around 20-ish kts.

After accelerating past 35kts I am confident de IAS is very well calibrated (I have crosschecked it ina zero wind day with GPS ground speed).