My flight school has several older Jabs online but I have only trained on one particular plane from day one.
Due to family commitments, flying now occurs on or near payday every month and sometimes every two months. It just so happened that one weekend that I intended to fly was particularly busy. There was only one plane left, same make/model that I trained on, but one i've never actually flown.
I have heard stories where the same make/model/engine will possibly fly differently to another. With a bit of disappointment, I reluctantly agreed to take her anyway as I was not prepared to wait another month to fly. Besides, I was intending to fly circuits only so no big deal or so I thought.
After an uneventful takeoff, I soon realise that the Airspeed Indicator was acting very wierd. I was on my downwind leg and it would indicate a normal 80kts one second, then jump to 120kts then back down again.
I didn't panic as I thought it could probably be the wind gusting ?!?! (at the time I thought it made sense). Anyway rather continue my circuits I decided to head out to the training area and check it out a little more. I decreased my speed to just above stall to see if it indicated a lower reading. It did. I thought to myself it's fine. But as soon as I sped up it would be erratic again.
At this point I was a little more concerned so I flew back to base and contacted my flight instructor on the radio to ask him if this particular plane had a speed calibration issues. He replied with a nonchalant "oh, yeah... just add 10kts to whatever the reading and you'll be fine "
Fine and dandy I thought, so off I went and continued with my circuits. On my base and final legs, I kept adding 10kts to what the ASI read. I looked out the window regularly and thought to myself: "plane is going too fast". Sure enough over the fence, and the plane floated and floated despite the fact that the ASI read 60kts (translates to 70kts after adding 10). Naturally I aborted the landing and went around.
At this point, I finally confirmed that my ASI is stuffed and that the 10kts crap was not going to fix the issue. In short I was in a pickle. So there I was again in the downwind leg with my ASI reading 95kts, my hands dripping with sweat, heart racing.
As a low-time pilot with only 15hrs solo experience, I then decide that I was not going to look at the ASI and instead listen to the RPM which is a good indicator anyway I thought.
I kicked myself for not taking my GPS along - at least that shows the ground speed (good enough on this windless day).
I recall during training that on the downwind my RPM should be around 2800, and just before turning base I should drop to 2100. By the time I turn final my descent should be around 500 feet/min adjusting the RPM as required to maintain this descent rate. I ignored the fact that on late final my ASI was showing only 50kts, however my hand never left the throttle to ensure full power at the first signs of a stall.
The landing was pretty smooth considering what was going on. It took about an hour to calm my nerves and realise what happened and what potentially might have happened.
A few weeks later, my instructor recalled my radio call to him and confirmed what I already knew, that the ASI was showing incorrect readings on that plane. The cause... a bug found its way in the pitot tube.
Last week I flew the same plane and surprise surprise, the pitot tube now has a cover !