What happened
While performing the downwind leg of a circuit at Djarindjin/Lombadina, the pilot of a Cessna 182 (registration VH-LHC) noticed an unexpected drop in manifold pressure from 20 to 17 inHg. Following this, the pilot lost the ability to regulate engine power via the cockpit throttle lever.
As the aircraft progressed through the base turn, the approach speed reached 20–25 kt above the recommended 75 kt threshold. Due to this excessive speed, the pilot determined there was insufficient runway remaining to complete a safe landing and initiated a go-around. During the climb attempt, the aircraft's speed began to decrease. Because the engine power could not be increased, the pilot was forced to level the aircraft and perform a left turn to maintain altitude.
The investigation
Investigators examined the throttle linkage and found that the connection had disconnected and the securing nut was missing. This disconnection meant that movements of the cockpit throttle lever were no longer transmitted to the engine's throttle arm.
Crucially, the investigation found that the engine side of the linkage did not move to the position required by manufacturer standards for a disconnection event. While certification requires a torsion spring to pull the throttle to at least 75% open to ensure continued safe flight, the throttle arm remained at a low power setting. The investigation concluded that the required torsion spring was likely not installed on the aircraft.
Furthermore, several installation errors were identified on VH-LHC. These included the use of an incorrect throttle arm, the use of a castellated nut and split pin instead of the specified reduced hex nut, and the likely incorrect placement of spacers. These inconsistencies created a risk of unintended component interactions that could lead to linkage failure.
Findings
- The loss of throttle control was caused by the failure of the throttle linkage securing mechanism.
- The aircraft approached the runway at a speed significantly higher than recommended, preventing a safe landing.
- The inability to sustain a climb during the go-around was due to the engine power remaining at a low setting, as the missing torsion spring failed to open the throttle to the required 75% position.
- Incorrect hardware and installation discrepancies increased the risk of the linkage disconnecting.