Pitot/Static Line or Fitting Cracks

Line or fitting cracks for either the pitot (ram air pressure) or static (outside air pressure)  that feed the Air Data Computers or standby Altimeter/Airspeed indicators, will cause splits in indications that the crews observe.

In flight..... a cabin air pressure leak into the static system will ALWAYS cause the altimeter indication to drop. A cabin air pressure leak into the pitot system will cause airspeed indications to rise. An airspeed split will be less noticeable at lower altitudes and more acute the higher the aircraft flies.

When we have leaks, they are most often found in "T"  and elbow fittings.
  
     
  
This was actually a "T" fitting feeding pitot pressure to one of the Air Data Computers. The crews were complaining of a 3 knot split at altitude.
  
     
  
To find these leaks we disconnect the line from the Air Data (which seals the system), and we pressurize the line with the Air Data Test Set. Then comes the fun job of spraying leak detector on all the lines until we find bubbles.

This latest leak was easy to find as it was the first fitting from the computer. Most of the time they're not that easy.

I attribute a lot of these to killing power to the aircraft in winter. The aircraft freeze and these fittings seem to crack at a faster rate. To me..... leaving the aircraft fully powered keeps all the electronic boxes running. The heat from those units will keep the E&E compartment and cockpit above freezing temperatures. Turning up instrument and panel background lights keeps things comfy also.