Flight instructor flying SR20 reported aerodynamic flutter on aileron surface.

Attributes
ACN	1642713
Time
Date	201905
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	SR20
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Direct
Flight Plan	None
Component
Aircraft Component	Aileron
Person 1
Function	Instructor Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 13 Flight Crew Total 2900 Flight Crew Type 189
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

35 - 40 minutes into the flight while on downwind we experienced a bouncing up and down of the aircraft - like a very fast light chop - a regular rhythmic motion at several times/ second. I saw that the right aileron was bouncing up and down at the trailing edge - oscillating. I then looked at the left aileron and saw that it was not bouncing up and down. Immediately; I told the pilot flying that we need to land the plane now. Intermittent; periodic oscillations continued to occur as we turned base; flaps 50% were deployed. Turn to final was completed and full flaps were deployed. Shortly after leveling from the turn to final the right aileron departed the aircraft.control was maintained and the aircraft continued on final without incident. The NTSB was notified of the incident later that evening. Prior to the incident flight; a preflight walk around was completed with no damage; issues noted. I did a full deflection control check while taxiing out for takeoff. No issues in control feel or deflection were noted.

Original NASA ASRS Text

Title: Flight Instructor flying SR20 reported aerodynamic flutter on aileron surface.

Narrative: 35 - 40 minutes into the flight while on downwind we experienced a bouncing up and down of the aircraft - like a very fast light chop - a regular rhythmic motion at several times/ second. I saw that the right aileron was bouncing up and down at the trailing edge - oscillating. I then looked at the left aileron and saw that it was not bouncing up and down. Immediately; I told the pilot flying that we need to land the plane now. Intermittent; periodic oscillations continued to occur as we turned base; flaps 50% were deployed. Turn to final was completed and full flaps were deployed. Shortly after leveling from the turn to final the right aileron departed the aircraft.Control was maintained and the aircraft continued on final without incident. The NTSB was notified of the incident later that evening. Prior to the incident flight; a preflight walk around was completed with no damage; issues noted. I did a full deflection control check while taxiing out for takeoff. No issues in control feel or deflection were noted.

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.