Narrative:

My student and I were practicing maneuvers. When we were about to turn left we looked out the window and saw that the left flap was down to at least 20 degrees and had serious structural damage. I checked to see if both flaps were at the same setting but the right flap was up. The flap lever was in the 0 degree position. I don't know what had caused it. I suspected that something had hit it because it looked severely damaged. I thought it was a bird because I don't know what else it could have been. I've never been in this situation before. I cut the lesson short and headed back to the airport for a full stop right away. I realized that to maintain control I had to press the right rudder pedal more and put in right aileron to counter the plane's movement. If I were to let the controls go it felt as if the plane would have rolled to the right and yawed to the left. I told the tower controller that we were inbound for a landing and that we had a left flap that was down and thus asymmetrical flaps. I wanted to give a sense of urgency. We were given the closest runway to us and I was okay with that as I just wanted to get down safely and as soon as possible. As we descended I did what I needed to keep the airplane at approximately 70 knots and aligned with the runway centerline. When we touched down the plane rolled to the left uncontrollably and made attempting a go around impossible without complete loss of control. I applied braking action to slow the plane down and keep us on the centerline and all my efforts were spent on slowing the plane down safely on the runway. The plane was uncontrollably being pulled left towards the grass and I did everything I could to stop it from getting off and as safely as I could. At the edge of the runway I was pressing on the brakes and still the plane would not stop heading towards the left. I was finally able to get the plane to a full stop. Tower then gave us instructions that we were to taxi onto a taxiway and contact ground control. I told either the tower controller that we were in the grass and that we might have struck a light. We contacted ground control and were given instructions to taxi to our ramp. Fire trucks were given instructions to follow us. Next time; I would remain calm; declare an emergency; ask for the longer runway and land on the side of center-line where there the flap isn't lowered to adjust for the additional asymmetrical drag and how it affects the airplane upon landing. I would also encourage more literature on how to deal with asymmetrical flap failures as well as an emergency checklist item for such a situation in pilot operating handbooks or in the FAA's educational literature such as the airplane flying handbook.

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Original NASA ASRS Text

Title: C172 flight instructor reported an asymmetric flap condition resulted in a difficult approach and landing; followed by a loss of control; runway excursion and contact with runway light.

Narrative: My student and I were practicing maneuvers. When we were about to turn left we looked out the window and saw that the left flap was down to at least 20 degrees and had serious structural damage. I checked to see if both flaps were at the same setting but the right flap was up. The flap lever was in the 0 degree position. I don't know what had caused it. I suspected that something had hit it because it looked severely damaged. I thought it was a bird because I don't know what else it could have been. I've never been in this situation before. I cut the lesson short and headed back to the airport for a full stop right away. I realized that to maintain control I had to press the right rudder pedal more and put in right aileron to counter the plane's movement. If I were to let the controls go it felt as if the plane would have rolled to the right and yawed to the left. I told the Tower Controller that we were inbound for a landing and that we had a left flap that was down and thus asymmetrical flaps. I wanted to give a sense of urgency. We were given the closest runway to us and I was okay with that as I just wanted to get down safely and as soon as possible. As we descended I did what I needed to keep the airplane at approximately 70 knots and aligned with the runway centerline. When we touched down the plane rolled to the left uncontrollably and made attempting a go around impossible without complete loss of control. I applied braking action to slow the plane down and keep us on the centerline and all my efforts were spent on slowing the plane down safely on the runway. The plane was uncontrollably being pulled left towards the grass and I did everything I could to stop it from getting off and as safely as I could. At the edge of the runway I was pressing on the brakes and still the plane would not stop heading towards the left. I was finally able to get the plane to a full stop. Tower then gave us instructions that we were to taxi onto a taxiway and contact Ground Control. I told either the Tower Controller that we were in the grass and that we might have struck a light. We contacted Ground Control and were given instructions to taxi to our ramp. Fire trucks were given instructions to follow us. Next time; I would remain calm; declare an emergency; ask for the longer runway and land on the side of center-line where there the flap isn't lowered to adjust for the additional asymmetrical drag and how it affects the airplane upon landing. I would also encourage more literature on how to deal with asymmetrical flap failures as well as an emergency checklist item for such a situation in pilot operating handbooks or in the FAA's educational literature such as the airplane flying handbook.

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.