Originally Posted by
QuagmireAirlines
If it was a total pressure (pitot) tube that was blocked, then I don't see how the crew would see an airspeed mismatch problem until about 30 or 40 knots on takeoff, since that's ram air pressure he blocked. Maybe I'm missing something here from the flawed and spotty reporting. ??
I guess somebody crazy is bound to do this once in a while. This guy accessed the aircraft on the tarmac, unusual at the time since the plane had no outstanding problem reports to fix.
Also, why did it take so long to arrest this dude? Sabotage happend in July, and he was arrested in Sept. I think they found and fixed the problem and knew the foam didn't just magically appear there.
If a pitot tube is completely blocked on the ground, and the barometric pressure falls substantially from what it was at the time the blockage occurred, the trapped pressure (compared to the still open static port), can cause the airspeed to show a positive reading. This happened once to me with a Gulfstream G200. The pitot tube cover was made of molded plastic and had no vent hole. Apparently it made a completely airtight seal when installed on the pilot side pitot tube. We installed the covers when bringing the aircraft into the hangar after a flight on a day when the barometric pressure was 30.45 in/hg. A few days later, I powered up the aircraft on the GPU to do a preflight maintenance check, when the barometric pressure was about 29.75 in/hg. I thought there was an ADC failure because the pilot airspeed was showing about 65 knots. It took a few minutes to figure out what was going on. After pulling the pitot cover off, the false airspeed reading disappeared. At least it proved that the pitot line from the tube to the ADC was completely leak free on that particular aircraft...