What happened
On March 8, 2017, at approximately 16:55, a Textron Aviation Inc. 172S, registration TF-FTO, was performing flight training maneuvers at Reykjavík Airport (BIRK). The flight, which involved a student pilot undergoing PPL renewal and a flight instructor, was executing touch-and-go landings on runway 13. While in the traffic pattern, the aircraft encountered a sudden jolt that caused the nose to pitch downward.
Upon attempting to correct the pitch, the student pilot found the elevator controls to be extremely heavy and difficult to move. The flight instructor took control of the aircraft to assess the situation and confirmed that the elevator was sluggish, could not be moved through its full range of motion, and exhibited a jerking sensation when manipulated. Other flight controls appeared to be functioning normally. To descend, the instructor utilized the aircraft's trim system and reduced engine power. The instructor then requested priority from Air Traffic Control and successfully completed a landing on runway 13 without further incident.
The investigation
Following the landing, the crew inspected the elevator control cables and observed that they appeared loose enough to be tightened by hand. A subsequent inspection by a maintenance technician revealed that a control cable running from the aircraft's control column to the elevator was not sufficiently tensioned. The technician's report indicated that the tension in the elevator control cable was at the minimum allowable limit according to the manufacturer's specifications. The tension was subsequently adjusted to the correct level.
Findings
- The primary cause of the control difficulty was insufficient tension in the elevator control cable.
- The low tension in the cable resulted in heavy, sluggish, and jerking elevator response.
- The investigation could not rule out the possibility that the cable had momentarily slipped from a pulley, which might explain the jerking sensation, though the primary finding remained the low tension level.