That was dumb!

SMO · #1 07-10-2011, 06:10 PM

Departing for a local pleasure flight today, I looked down at my ASI on initial climb out expecting to see the needle on 100 or so and was shocked to see it wavering between 75 and 80. I lowered the nose from my normal 1500 - 2000 ft/min climb to 1000, the ASI initially did not respond, then slowly began climbing. But I knew it wasn't right, the airplane was running good, full rpm, full fine prop. As I flew downwind the first thought was to land, after all my ASI wasn't working properly. However I pretty soon rejected that idea. I really don't need the ASI for a local flight and I wanted to get up high and do a couple stalls to see what the ASI did on the bottom end. So away I went, and the airspeed slowly seemed to sort itself out. Slowing down and speeding up the ASI appeared to operate normally between 100 and 160, and I could confirm this with the GPS. However below 100 it seemed to read high, validated by the stall occurring at a reading of 65 - 70 when it should be about 50. So now I know to forget about looking at the ASI when I land. I then did 2 - 3 approaches to the stall just to refresh myself regarding the feel of this flight regime - I know the controls get loose at about 10 mph above the stall and I wanted to make sure I recognized that. I don't trust the GPS during the approach, between wind and sink it just isn't reliable enough for my liking.

When I took my transition training with Mike Seagar in his RV-7, we had one flight where we lost the ASI due to the static line being plugged (got water in it). It made me nervous, so much so I asked Mike to take the landing. However I guess I have flown my -4 enough as I was not nervous at all as I set up for a normal approach (maybe just too dumb to be nervous). The approach worked out well, adjusting attitude for airspeed whenever the stick got a little loose, and throttle for elevation as required. Ended up making one of my better landings.

I'll pull the boot cowl tomorrow and blow out the pitot line and the static line. The last while the airplane has been left under cover but not indoors, and I haven't had the pitot covered. For sure THAT was dumb!

terrye · #2 07-10-2011, 06:22 PM

Be careful "blowing out" the static line, it's easy to damage the instruments attached to them. Probably best to disconnect them completely.

CPSONE · #3 07-11-2011, 10:59 AM

Were your altimeter and VSI working fine?
Probably just a pitot blockage if so.
Had it happen in a C180 on floats once...While giving a float endorsement.
Good lesson! Stopped in the middle of the lake, cleaned the bee parts out of the pitot tube and good as new.
Good to check complete pitot / static system as you mentioned.
God job identifying the problem and dealing with it!

SMO · #4 07-11-2011, 10:57 PM

Blew out the static and the pitot, didn't see any crud exit but went for a test flight and ASI is working again. I was careful not to pressurize any of the instruments - just disconnected at the tee before the first instrument and blew out the line from there.