201 Gear Safety vs ASI

[201er]

I've had some strange indications on the ASI lately (speed erroneously dropping off after takeoff, pull alternate air, stabilizes and ok) so I brought it to avionics shop to get Pitot/Static tests done early and diagnose. First he thought ASI was broken cause it was consistently reading 8-12 knots wrong on tests. But as he was about to remove it, he discovered a "mysterious box" connected off the pitot system that I suspect to be the gear retraction prevention device on the '78+ 201s.

 

Now my question is this... how could that affect the ASI readings and is it possible that somehow the process of gear retraction creates feedback on this device? In retrospect the funky readings were always 5-20 seconds after gear retraction. Any ideas?

[M016576]

None on that, but good thing you've got an AoA indicator... 10-12 knots off on the ASI could spell tragedy if you didn't...

[N201MKTurbo]

it could have a leak.

[jetdriven]

Check for water in the rear static drain. I flew with a guy in a 201 after it rained hard the night before. At rotation, the airspeed rolled back to zero, the altimeter and VSI froze, and the Aspen went black and red-x'ed.  It only took a couple drops of water to do that.

[fantom]

Now my question is this... how could that affect the ASI readings ....Any ideas?

 

Obviously a case of undetected windscreen parrot droppings encasing the ASI.

[Marauder]

Mike -- as you know, there is also a front pitot drain. I had to replace that O ring a couple of times in the 22 years of ownership. Are you sure the mysterious black box is the airspeed switch? I thought the airspeed switch was physically mounted to the back of the ASI in your vintage Mooney. Don't some autopilots have airspeed select features? Also, when was the last time you had your airspeed indicator looked at? If it is original, you might want to consider a rebuild. It will cost around $300 and you will get a new painted face on it. What other gizmos you have in your plane that could take advantage of a pitot source? At this point, just throwing out ideas at you... I know how desperately you want your airspeed back!

[carusoam]

I wrote this last night, but it wouldn't post. Internet access issue....

A few thoughts...

(1) Anything attached to the ASI system could potentially cause a leak.

(2) A leak in the pressurized pitot system would appear as a drop in airspeed. (is that what you're seeing?)

(3) a pressure sensor in the line would not know if the gear was moving or not.

(4) if the sensor installation was leaking, it would leak all the time.

(5) if the sensor itself is leaking, it may leak when the gear is "allowed" to retract.

Sounds to me, that the mechanical pressure switch that supplies a signal to the gear actuation system, may have a leak when the switch is thrown by the pressure increasing in the pitot system.

Check the switch for leaks...

Sorry I don't have experience with the system. How does my logic sound?

Best regards,

-a-