Airspeed Indicator

[mocfly]

Went to the hanger today with the intention of checking the balance of the carbs and found something interesting.

When I looked at the ASI it read 20 knots. Took the panel off, disconnected the pitot line and the airspeed went to 0. Checked the pitot line all clear. Re-connected the pitot line still reading 0.

 

I am really curious about the cause?

 

[Madhatter]

Check the static line. Verify that you disconnected the pitot line and not the static line. An obstruction in either pitot or static line can cause this problem. Make sure static line is tight when you reconnect it.

[mocfly]

The lines are marked for identification. They have neat little tags that say PITOT and the other STATIC. As are the corresponding ports on back of the ASI.The first line I took off was the static line no change. Reinstall the static line and then remove the pitot line. When the pitot line was removed the speed went to 0.

 

[Mike]

Probably water in the pitot line this would allow you to blow through it disconnected but still block it for your Asi

 

Mike

[FredG]

Chris, that is hard to explain. Since there was an apparent obstruction when it read 20 kts (evidenced by the drop to zero when you disconnected the pitot tube), it is hard to understand how it was then observed to be clear. Mike offered a reasonable explanation.

 

Have you flown again since this happened? It would be very interesting to know if it was a one time problem or if it recurs. How did you check the pitot line (ie, from the panel end or from the pitot tube end)?

[Jim Meade]

When a static system is breached and reassembled, is it supposed to get a leak test from a facility authorized to work on them? We don't want to fly around with someone's altimeter out of whack by a couple of hundred feet.

[Roger Lee]

Hi Jim,

 

The LSA don't fall under the same rules that GA or IFR rated static system test are held under. No on going test is required. It would be wise to get it checked, but not required.

[FastEddieB]

My guess is tiny water bubble in one of the lines.

 

Oh, and Jim is technically right.

 

Rather than harp upon it maybe someone (me?) should start a thread about what an S-LSA owner can and can't do, maintenance-wise, at which point owners can do what they want with that information.

[Roger Lee]

The static system can't be worked on by the owner unless he is a mechanic or has an ELSA. The static system is not required to have a test every 24 months like the transponder. If you open the static line up (i.e. on the back of the D100) there is no reg that says it must be tested by an authorized facility for an LSA.

[mocfly]

I can assure you that there was no water in the line.

 

[Jim Meade]

My Operating Limitations say the instruments and equipment installed and used under 91.205 must be inspected and maintained in accordance with the requirements of part 91 and must be recorded in the maintenance records. I would think that would at a minimum apply to night flight.

 

 

[Roger Lee]

Part 91 has sub paragraphs in areas which change some items for LSA. That is part of the problem. Many of the regs we know because of GA experience and have learned them that way, but if you really read some they have sub paragraphs that either add something or remove something or re-direct you to some where else related to LSA. Sometimes it boils down to the fine print which can make it confusing if you don't read every little section. I have certainly been there.