As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A HIGH POWER GROUND MAINTENANCE RUN-UP, THE MECHANIC IN THE COCKPIT OBSERVED THAT THE BLEED AIR PRESSURE SUDDENLY DROPPED TO NEAR ZERO, FROM 40 AND PSI. INVESTIGATION REVEALED THE LEFT HP AIR PRECOOLER HAD FAILED (BLOWN), EFFECTIVELY OPENING THE BLEED AIR MANIFOLD, NO OTHER DAMAGE WAS DONE. EXTREME AGE OF THE PART IS THE MOST LIKELY CAUSE.