What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Airspeed fluctuations

mckay57

Member
We have the legacy G3X system, with a backup (round dial old school) airspeed indicator. The plane passed IFR pitot/static test a few months ago. Our airspeed indicators (both the electronic one through the G3X and the old school back round dial one), both have started fluctuating up to 15 to 20 knots. It comes up to speed, then both dropped really quickly (a second or 2), then slowly climb back up. It pulses like this through the entirety of the flight. The faster and higher you go, the bigger the variation. Pitot blockage??
Don
 
We have the legacy G3X system, with a backup (round dial old school) airspeed indicator. The plane passed IFR pitot/static test a few months ago. Our airspeed indicators (both the electronic one through the G3X and the old school back round dial one), both have started fluctuating up to 15 to 20 knots. It comes up to speed, then both dropped really quickly (a second or 2), then slowly climb back up. It pulses like this through the entirety of the flight. The faster and higher you go, the bigger the variation. Pitot blockage??
Don

I'd look for leaks in the static plumbing.
 
We have the legacy G3X system, with a backup (round dial old school) airspeed indicator. The plane passed IFR pitot/static test a few months ago. Our airspeed indicators (both the electronic one through the G3X and the old school back round dial one), both have started fluctuating up to 15 to 20 knots. It comes up to speed, then both dropped really quickly (a second or 2), then slowly climb back up. It pulses like this through the entirety of the flight. The faster and higher you go, the bigger the variation. Pitot blockage??
Don

That would be a decent guess. Something deep inside the pitot that is moving around. This would explain why it doesn't start doing it untill the pressure gets high enough inside. Could also be a unique kind of leakage, where the pressure builds to certain critical point, then it opens and releases some of that pressure down to the lower critical point, re-seals and it starts all over again. Not all leaks are constant. Some will hold up to a certain pressure and then fail.
 
Last edited:
As others have mentioned, if your altimeter and VS is sable, then I would look into your pitot tube and pitot line. For the IFR test, they don't use your pitot, only your static lines.
 
Classic Water in pitot lines sympotoms

Almost sounds like water somewhere in the pitot lines…..

Only time and proof will tell but the thread starters described symptoms match classic water in the pitot lines .

Any chance you have flown in rain or washed your AC with a hose or pressure washer?
 
Solved

We found a small amount of a oily substance in the pitot tube. Not much, but it was apparently enough to move around and cause the fluctuations. Test flew it today, and everything is fine now. We have no idea what the oily substance was or how it got in the pitot. Really strange. Thanks guys for all your input
 
Back
Top