Narrative:

Fl 350; profile; autopilot 1 engaged; .78 mach; ground speed approximately 480. Optimum alt 350; max 370. Autopilot 2 deferred. Filpz one arrival to clt; line check airmen (lca) captain giving IOE to first officer. Captain was pilot monitoring (pm); first officer (first officer) was pilot flying. Clearance to cross skywa intersection at 330. First officer put 330 in fcp; I added a constraint to FMS to cross skywa at fl 330. I had unspoken concerns that the FMS computed descent point was too close to assigned constraint. ATC gave frequency change; prior to checking in I directed first officer to select immediate descent at approximately 11 miles from skywa. I checked in with center leaving 350 with clearance to cross skywa at 330. They acknowledged. Descent was proceeding normally at 1;000 fpm; shortly after going thru fl 340; FMS picked up its computed profile and increased its descent rate to honor constraint. I recognized at 33;200 feet that the autopilot was not going to capture fl 330. Descent rate was approximately 2;000 fpm and not decreasing. I directed first officer to disengage the autopilot and manually level the aircraft. While the autopilot disconnect warning was going off I decided to take control of the airplane. In normal conversational tone I announced I had the aircraft; and I punched off the autopilot warning and began level off. As I put in back pressure to level off I was surprised that the aircraft entered a buffet. I released back pressure; the buffet stopped; aircraft altitude was now about 32;850. I added a small amount of back pressure back in to climb back to our assigned altitude and the buffet reoccurred. I released back pressure; allowed the aircraft to stabilize 150 below our assigned altitude for about 10 seconds and then manually climbed back up to FL330. During that time I confirmed the speed brake was retracted. I directed the first officer to reengage autopilot 1 and to select alt hold. He completed the descent from altitude with autopilot 1 engaged using level change without further issue. I wrote the incident up in the logbook in detail and also gave clt maintenance a thorough verbal debriefing. Neither the first officer or I felt we induced enough G on the aircraft to induce the buffet; control inputs seemed smooth to both of us with little noticeable G force. During post flight conversation I discovered the first officer did not hear me take control of the airplane due to the blaring autopilot disconnect warning and he also did not realize I was putting inputs to the controls. I too did not notice his inputs or ever felt they were contrary to mine. He stated he was also putting inputs in; and from what both of us could tell; his inputs mirrored mine and vice versa. Neither one of us felt at any time that the aircraft response was anything other than what we expected considering the inputs we were applying. The initial manual level off that resulted in the first airframe buffet did not seem aggressive or abrupt to either of us nor did the first attempt to climb back to our assigned altitude which resulted in the second airframe buffet. Stick shaker did not occur at any time. We both completed a visual walk around inspection of the aircraft after landing and noticed nothing unusual. I informed the first officer I was submitting [a safety] report and advised him to do the same so causes and errors could be identified and others could gain awareness and knowledge. Maintenance action post flight revealed no system anomalies; ACARS showed lateral g of .15; inspection showed no aircraft damage.

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Original NASA ASRS Text

Title: While enroute to CLT and beginning descent; the autopilot failed to capture an intermediate altitude. Both crewmembers disconnected the autopilot and corrected back to altitude at the same time which may have resulted in a slight overcorrection and associated airframe buffet.

Narrative: FL 350; profile; autopilot 1 engaged; .78 Mach; ground speed approximately 480. Optimum alt 350; max 370. Autopilot 2 deferred. FILPZ one arrival to CLT; Line Check Airmen (LCA) Captain giving IOE to FO. Captain was Pilot Monitoring (PM); First Officer (FO) was Pilot Flying. Clearance to cross SKYWA intersection at 330. FO put 330 in FCP; I added a constraint to FMS to cross SKYWA at FL 330. I had unspoken concerns that the FMS computed descent point was too close to assigned constraint. ATC gave frequency change; prior to checking in I directed FO to select immediate descent at approximately 11 miles from SKYWA. I Checked in with center leaving 350 with clearance to cross SKYWA at 330. They acknowledged. Descent was proceeding normally at 1;000 fpm; shortly after going thru FL 340; FMS picked up its computed profile and increased its descent rate to honor constraint. I recognized at 33;200 feet that the autopilot was not going to capture FL 330. Descent rate was approximately 2;000 fpm and not decreasing. I directed FO to disengage the autopilot and manually level the aircraft. While the autopilot disconnect warning was going off I decided to take control of the airplane. In normal conversational tone I announced I had the aircraft; and I punched off the autopilot warning and began level off. As I put in back pressure to level off I was surprised that the aircraft entered a buffet. I released back pressure; the buffet stopped; aircraft altitude was now about 32;850. I added a small amount of back pressure back in to climb back to our assigned altitude and the buffet reoccurred. I released back pressure; allowed the aircraft to stabilize 150 below our assigned altitude for about 10 seconds and then manually climbed back up to FL330. During that time I confirmed the speed brake was retracted. I directed the FO to reengage autopilot 1 and to select alt hold. He completed the descent from altitude with autopilot 1 engaged using level change without further issue. I wrote the incident up in the logbook in detail and also gave CLT maintenance a thorough verbal debriefing. Neither the FO or I felt we induced enough G on the aircraft to induce the buffet; control inputs seemed smooth to both of us with little noticeable G force. During post flight conversation I discovered the FO did not hear me take control of the airplane due to the blaring autopilot disconnect warning and he also did not realize I was putting inputs to the controls. I too did not notice his inputs or ever felt they were contrary to mine. He stated he was also putting inputs in; and from what both of us could tell; his inputs mirrored mine and vice versa. Neither one of us felt at any time that the aircraft response was anything other than what we expected considering the inputs we were applying. The initial manual level off that resulted in the first airframe buffet did not seem aggressive or abrupt to either of us nor did the first attempt to climb back to our assigned altitude which resulted in the second airframe buffet. Stick shaker did not occur at any time. We both completed a visual walk around inspection of the aircraft after landing and noticed nothing unusual. I informed the FO I was submitting [a safety] report and advised him to do the same so causes and errors could be identified and others could gain awareness and knowledge. Maintenance action post flight revealed no system anomalies; ACARS showed lateral g of .15; inspection showed no aircraft damage.

Data retrieved from NASA's ASRS site 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.