Narrative:

Early morning trip from ord. Jet had come from [maintenance] the day before and had last been flown by [test] pilots. All was normal except during taxi-out I forgot to call for flaps and after start checklist (likely due to having had the last 12 days off). We did catch it when [first officer] did after start flow and takeoff configuration horn went off. Thankfully; it was a good reminder that the biggest threat could be our early [morning] departure and circadian disruption. During taxi-out brakes heated up. As we were number 1 for takeoff; checked brakes and they were at 270 on right side and rising. Climbing through 4;000 feet; checked temperature and it was rising through 290. Not wanting to get the hot brakes ECAM I engaged autopilot; retracted flaps on schedule; maintained 210 knots in climb; extended gear to allow it to cool and advised ATC of slow climb rate. Gear immediately began to cool and as soon as it trended down from 270 we retracted gear; resumed normal climb out and accelerated above 10;000 feet.climbing through FL230 we were accelerating to 315 KIAS (we were running behind schedule). As airspeed increased through 305 KIAS very light buffet (similar to mach buffet) started. As we accelerated on the autopilot through 310 knots the buffet got much worse (nearly moderate; significant enough that it would have spilled my cup of coffee if I had one). First officer and I agreed a course reversal back to ord and [ATC communication] was warranted. Accomplished both. I kept autopilot on to reduce workload and reversed climb to vertical speed -1000 FPM descent and selected speed of 250 knots. Biggest concern was if we had lost a fairing or flap canoe or if vibration returned and aileron separated from jet. The previous flight was a test flight which was conducted; in part; due to aileron replacement. Conducted abbreviated briefing over public address with flight attendants (jet had no passengers). 'Hello gang; that vibration we just had was not normal or wake turbulence. We are not sure what caused it; so we would like you to immediately take your jumpseats and we are going to return to land at ord.' conducted normal approach and landing; albeit got stabilized 3 miles prior to marker for 28C. After asking [crash fire rescue] to describe any visible damage or anything out of the ordinary (they said all looked normal); we taxied to [our] hangar. First officer did a fantastic job of handling the duties and coordinating with ATC while I chatted with dispatch. Communications with dispatch/maintenance was difficult due to the company disabling the discrete VHF communication frequencies we used to utilize for calling directly to [operations]. Arinc was mostly unreadable which increased workload and tension. After course reversal; I did reference the QRH airframe vibration checklist as a review. Elected to discontinue any type of troubleshooting or identification (as called for in QRH) due to the severity of the vibration and task prioritization (aviate; navigate; communicate). ATC could not have been more helpful.

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Original NASA ASRS Text

Title: A320 flight crew reported returning to departure airport after significant airframe vibration during climb.

Narrative: Early morning trip from ORD. Jet had come from [Maintenance] the day before and had last been flown by [test] pilots. All was normal except during taxi-out I forgot to call for flaps and after start checklist (likely due to having had the last 12 days off). We did catch it when [First Officer] did after start flow and takeoff configuration horn went off. Thankfully; it was a good reminder that the biggest threat could be our early [morning] departure and circadian disruption. During taxi-out brakes heated up. As we were number 1 for takeoff; checked brakes and they were at 270 on right side and rising. Climbing through 4;000 feet; checked temperature and it was rising through 290. Not wanting to get the Hot Brakes ECAM I engaged autopilot; retracted flaps on schedule; maintained 210 knots in climb; extended gear to allow it to cool and advised ATC of slow climb rate. Gear immediately began to cool and as soon as it trended down from 270 we retracted gear; resumed normal climb out and accelerated above 10;000 feet.Climbing through FL230 we were accelerating to 315 KIAS (we were running behind schedule). As airspeed increased through 305 KIAS very light buffet (similar to mach buffet) started. As we accelerated on the autopilot through 310 knots the buffet got much worse (nearly moderate; significant enough that it would have spilled my cup of coffee if I had one). First Officer and I agreed a course reversal back to ORD and [ATC communication] was warranted. Accomplished both. I kept autopilot on to reduce workload and reversed climb to Vertical Speed -1000 FPM descent and selected speed of 250 knots. Biggest concern was if we had lost a fairing or flap canoe or if vibration returned and aileron separated from jet. The previous flight was a test flight which was conducted; in part; due to aileron replacement. Conducted abbreviated briefing over Public Address with Flight Attendants (jet had no passengers). 'Hello gang; that vibration we just had was not normal or wake turbulence. We are not sure what caused it; so we would like you to immediately take your jumpseats and we are going to return to land at ORD.' Conducted normal approach and landing; albeit got stabilized 3 miles prior to marker for 28C. After asking [Crash Fire Rescue] to describe any visible damage or anything out of the ordinary (they said all looked normal); we taxied to [our] hangar. First Officer did a fantastic job of handling the duties and coordinating with ATC while I chatted with Dispatch. Communications with Dispatch/Maintenance was difficult due to the company disabling the discrete VHF communication frequencies we used to utilize for calling directly to [Operations]. ARINC was mostly unreadable which increased workload and tension. After course reversal; I did reference the QRH Airframe Vibration checklist as a review. Elected to discontinue any type of troubleshooting or identification (as called for in QRH) due to the severity of the vibration and task prioritization (aviate; navigate; communicate). ATC could not have been more helpful.

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.