Flight instrument fluctuations

Kyle · Post by **Kyle** » Sat Jun 03, 2006 1:38 pm

Hi Folks,

Was flying the other day and observed an irregularity with the airspeed indicator and altimeter. Normal cruise is about 118-120 indicated.

In level flight, with no change in power setting, the airspeed indicator and altimeter started to climb (simultaneously). The airspeed climbed up in about 8-10 seconds to about 128 - then abruptly dropped to about 118, then climbed up to about 125-126, then abruptly dropped to a lower reading of about 114-116.

This same pattern continued for the remainder of the last 15 minutes of the flight. Each time it would not climb as high and dropped slightly lower. It was down to about 100 upon reaching the pattern.

The altimeter was doing the same thing.... the needle climbed and dropped in concert with the airspeed indicator.

I'm thinking something (water or a bug) got into the static line. Flight was day VFR and I have not observed this before

Any thoughts???

Thanks in advance,

Post by **Bruce Fenstermacher** » Sat Jun 03, 2006 2:03 pm

Kyle, I think you figured it out. Look for a blocked static port.

jrenwick · Post by **jrenwick** » Sat Jun 03, 2006 2:39 pm

If the static port were simply blocked, it doesn't seem like that would completely explain the behavior.

But if there were water in the static line, and the water was being drawn up the line a little way and then ran back down....

But that would mean air is continuously moving through the static line, so according to my theory there would also have to be a leak in the static system somewhere.

The avionics shop that checks your transponder every 24 months would have the equipment and experience to find a leak and fix this problem, if my theory is right!

Best Regards,

John

N2255D · Post by **N2255D** » Sat Jun 03, 2006 9:10 pm

I had a similar problem when I first got my plane. Found just a couple drops of water in the elbow off the static port. No problems since then.