Narrative:

This pilot requested lower altitude (he was at FL350). I advised him I could not get him lower because of traffic at 12 O'clock, 5 mi, at FL330. Because I only own FL350 and above, I called the sector below me to coordinate lower altitude. While on the handoff line with him I noticed that this aircraft had already started its descent which caused me to have less than standard separation. I asked the pilot why he was not able to maintain his altitude, and his answer was his airspeed was too slow to stay at altitude. In my mind that meant he stalled his aircraft. Supplemental information from acn 104329: on air carrier medium large transport from phl to mia on J79 southwest of sby VOR, we were cleared to FL350. Current conditions were visibility unlimited, VMC conditions. The aircraft weighed approximately 130000 pounds. In reference to the performance charts and this pilot's experience, the aircraft was fully capable of flying at FL350. After leveling at FL350, airspeed began to slowly decrease approaching low speed buffet. We immediately requested a descent to a lower altitude and the controller responded, 'unable.' shortly thereafter a light buffet was felt and I began a gradual descent of 300 FPM. The copilot told center that we had to descend now, asked for an off course heading and reported traffic in sight at 2-3 O'clock. The controller did not answer. We immediately called again and he gave us a heading change to the left. During this evolution, approximately 1 min passed and we had descended 300-400'. When the light buffet started, for safety considerations, an immediate descent was unavoidable. As soon as the descent was initiated the buffet ceased and airspeed increased. We were eventually cleared to FL310 where the flight continued uneventfully.

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Original NASA ASRS Text

Title: ACR MLG UNABLE TO MAINTAIN ALT DUE TO ACFT LIMITATIONS DESCENDED WITHOUT ATC AUTHORIZATION.

Narrative: THIS PLT REQUESTED LOWER ALT (HE WAS AT FL350). I ADVISED HIM I COULD NOT GET HIM LOWER BECAUSE OF TFC AT 12 O'CLOCK, 5 MI, AT FL330. BECAUSE I ONLY OWN FL350 AND ABOVE, I CALLED THE SECTOR BELOW ME TO COORDINATE LOWER ALT. WHILE ON THE HDOF LINE WITH HIM I NOTICED THAT THIS ACFT HAD ALREADY STARTED ITS DSCNT WHICH CAUSED ME TO HAVE LTSS. I ASKED THE PLT WHY HE WAS NOT ABLE TO MAINTAIN HIS ALT, AND HIS ANSWER WAS HIS AIRSPD WAS TOO SLOW TO STAY AT ALT. IN MY MIND THAT MEANT HE STALLED HIS ACFT. SUPPLEMENTAL INFO FROM ACN 104329: ON ACR MLG FROM PHL TO MIA ON J79 SW OF SBY VOR, WE WERE CLRED TO FL350. CURRENT CONDITIONS WERE VISIBILITY UNLIMITED, VMC CONDITIONS. THE ACFT WEIGHED APPROX 130000 LBS. IN REF TO THE PERFORMANCE CHARTS AND THIS PLT'S EXPERIENCE, THE ACFT WAS FULLY CAPABLE OF FLYING AT FL350. AFTER LEVELING AT FL350, AIRSPD BEGAN TO SLOWLY DECREASE APCHING LOW SPD BUFFET. WE IMMEDIATELY REQUESTED A DSCNT TO A LOWER ALT AND THE CTLR RESPONDED, 'UNABLE.' SHORTLY THEREAFTER A LIGHT BUFFET WAS FELT AND I BEGAN A GRADUAL DSCNT OF 300 FPM. THE COPLT TOLD CENTER THAT WE HAD TO DSND NOW, ASKED FOR AN OFF COURSE HDG AND RPTED TFC IN SIGHT AT 2-3 O'CLOCK. THE CTLR DID NOT ANSWER. WE IMMEDIATELY CALLED AGAIN AND HE GAVE US A HDG CHANGE TO THE LEFT. DURING THIS EVOLUTION, APPROX 1 MIN PASSED AND WE HAD DSNDED 300-400'. WHEN THE LIGHT BUFFET STARTED, FOR SAFETY CONSIDERATIONS, AN IMMEDIATE DSCNT WAS UNAVOIDABLE. AS SOON AS THE DSCNT WAS INITIATED THE BUFFET CEASED AND AIRSPD INCREASED. WE WERE EVENTUALLY CLRED TO FL310 WHERE THE FLT CONTINUED UNEVENTFULLY.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.