What happened
On the night of 30 March 2009, a Fairchild SA227-AC Metroliner III, registered ZK-NSS, departed Auckland International Airport on a medical transport mission to New Plymouth. The flight carried two pilots and a three-person medical crew. While the flight proceeded normally until the arrival phase, the approach to New Plymouth Aerodrome became problematic.
Departing from standard operating procedures, the crew initiated a visual approach at an uncontrolled aerodrome that lacked approach slope indicator lights. During the descent, the crew became preoccupied with an anomaly where the right engine failed to reach the selected high speed. This distraction, combined with a steep descent rate during a base turn near the aerodrome, triggered ground proximity warnings.
As the aircraft neared the runway, the pilots realized they were on a glide path that would result in landing near the very end of the runway. The pilot flying reported difficulty maintaining control when attempting to increase power, which he attributed to the engine issue. Rather than executing a go-around, the pilot decided to continue the landing. The aircraft struck the runway with significant force and immediately exited the side of the paved surface. There were no injuries to the five occupants, and the aircraft sustained only minor damage to its tires.
The investigation
The investigation focused on the decision-making process during the approach and the mechanical state of the engines. Investigators examined why the crew opted for a visual approach despite operator restrictions and why the unstable approach was not corrected. The inquiry also looked into a subsequent engine issue involving a fuel bypass event that occurred a few days later, though this was ultimately deemed unrelated to the New Plymouth excursion.
Findings
Several contributing factors led to the runway excursion:
- The approach was rushed because the crew began their visual descent too close to the aerodrome.
- The absence of approach slope indicator lights prevented the pilots from having a reliable reference for a stable descent.
- The pilots failed to execute a go-around despite encountering ground proximity warnings and an unstable glide path.
- Distractions caused by the right engine's failure to reach the commanded speed diverted the crew's attention from flight path monitoring.
- A lack of effective cockpit resource management and a potential imbalance in cockpit authority prevented the pilot not flying from intervening during the unstable approach.
- The pilot flying's perception of control difficulties during power adjustments contributed to the heavy landing at the runway threshold.