As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING UNSCHEDULED TEST OF PILOT'S PITOT/STATIC SYSTEM, DETERMINED A SUBSTANTIAL LEAK EXISTED. THE LEAK WAS TRACED TO THE HORIZONTAL STABILIZER DE-ICE SYSTEM DIFFERENTIAL PRESSURE SWITCH (REF: DESIGNATION S39B). THE UNIT IS LEAKING FROM PITOT TO STATIC SIDE INTERNALLY. RECOMMEND CHECKING PITOT/STATIC SYSTEM FOR LEAKS WHENEVER THERE IS A SIGNIFICANT MISMATCH BETWEEN NR 1 AIRSPEED AND NR ALTIMETER.