Fluctuating altimeter on takeoff

[AA5Bman]

Hi all - I have been thinking about buying a turbo 206 and went to test fly one recently. One thing I noticed is that when the owner’s pilot applied full throttle at takeoff, the altimeter bounced around wildly (+/-200 feet for 1-2 seconds) but then settled down and remained steady the remainder of flight. What could possibly cause this? The thing absolutely ripped, and it occurs to me that maybe there’s so much air moving past the static ports and pressure change when the throttle is applied that it causes erroneous readings and is normal, but I don’t think I’ve ever heard of or seen this before. Anyone ever seen anything like this, or have an opinion on whether or not this is an indication the pitot/static system is due for major repairs?

 

[sansoneservices]

Hi all - I have been thinking about buying a turbo 206 and went to test fly one recently. One thing I noticed is that when the owner’s pilot applied full throttle at takeoff, the altimeter bounced around wildly (+/-200 feet for 1-2 seconds) but then settled down and remained steady the remainder of flight. What could possibly cause this? The thing absolutely ripped, and it occurs to me that maybe there’s so much air moving past the static ports and pressure change when the throttle is applied that it causes erroneous readings and is normal, but I don’t think I’ve ever heard of or seen this before. Anyone ever seen anything like this, or have an opinion on whether or not this is an indication the pitot/static system is due for major repairs?

If your theory is correct (and may be) the moving air past the static port could cause a brief incorrect reading for the sudden rush of air but doesn't justify "bounced around wildly".. you could temporarily swap out the altimeter if you have access to one

 

[Jim Carpenter]

Start simple. I don't recall if the 206 has static line drains, open those and check for moisture. Also, try a takeoff with alternate static open just to see if that eliminates the effect.

 

[Bell206]

Anyone ever seen anything like this, or have an opinion on whether or not this is an indication the pitot/static system is due for major repairs?

Some airplanes and helicopter will experience this phenomenon. As long as the reading stabilizes and does not continue there shouldn’t be an issue with the system.

 

[3393RP]

Some airplanes and helicopter will experience this phenomenon. As long as the reading stabilizes and does not continue there shouldn’t be an issue with the system.

It's obviously reasonable the air disturbances around the pitot system components immediately following application of takeoff power in a high powered airplane could cause momentary fluctuations in airspeed indication. A 200' change in altitude display is a tiny change in pressure, .2" Hg.

Your recommendation is much better than just "doing something."

Besides, it's not the OP's aircraft. He was flying it for consideration of purchase.

 

[Dana]

Could be water in the pitot or static lines.

 

[Let'sgoflying!]

(+/-200 feet for 1-2 seconds)

None of the airplanes I fly or have flown did this.
I'd look into it.
I like the 'starting with water in the static system' idea written above.

 

[Ed Haywood]

Where are the static ports located? If one is on the left side of the fuselage aft of midship, it's going to get a slap of propwash when power is applied while stationary.

 

[NordicDave]

It's harder and more difficult to get mechanical gauges repaired correctly. Seems like the many of the people with these skills are aging out and retiring with some of the shops we all counted on in the past are no longer delivering the same quality. The era of digital is here and stuff like GI-275's are so much better than chasing mechanical gauge issues. Just one pilot's experience & view.

Checking the basics like the lines are clear is logical, but a long shot. I'd bet on the rubber bits and diaphragms aging out. When was the altimeter last replaced? That might be my guide if in your shoes for a pre-buy.