What happened
On the early morning of 20 July 2001, a Partenavia P68B, registration ZK-DMA, was conducting a scheduled night courier flight from Auckland International Aerodrome to Whangarei. While cruising at 5,000 feet, the aircraft encountered rain and thunderstorm activity. Shortly after, the pilot noticed a drop in fuel flow to the left engine, which subsequently lost power. During the subsequent attempt to manage the emergency, the right engine also experienced a significant power loss.
While flying in instrument meteorological conditions, the pilot attempted an emergency landing at North Shore Aerodrome. Despite the pilot's efforts to locate the runway lighting in the dark, the aircraft touched down at a high ground speed on the wet runway. The aircraft failed to stop within the runway limits, overrunning the end of the pavement, passing through a fence, and crossing a road before coming to rest in another fence. The pilot, the sole occupant, sustained moderate injuries to the face and ankle.
The investigation
Investigators examined the atmospheric conditions and the aircraft's mechanical state. The investigation established that the aircraft was airworthy and properly maintained. However, the aircraft encountered weather conditions—including rain, sleet, or hail—that were highly conducive to engine intake icing.
Technical analysis focused on the engine air intakes, which were susceptible to blockages from frozen precipitation. The investigation also reviewed the pilot's actions during the engine failure sequence, specifically the decision-making process regarding the use of the engine's alternate air system.
Findings
- The engine air intakes likely became blocked by ice, hail, or sleet, leading to the simultaneous loss of power in both engines.
- The pilot likely dismissed the possibility of icing because there was no visible ice build-up on the wings and the outside air temperature gauge indicated a positive 2° Celsius.
- Because the pilot did not consider icing a factor, the necessary corrective action—selecting the engine alternate air intake—was not performed. Had the alternate air had been selected, engine power could have been restored.
- The aircraft's flight manual warning for the P68B was found to be insufficiently clear regarding the use of alternate air in high-humidity environments at temperatures above freezing.
Safety action
Following the inquiry, the flight manual for the Partenavia P68B was amended to instruct pilots to use the engine alternate air whenever flying in high humidity, regardless of the ambient temperature. Additionally, the operator was advised to remind pilots of the aircraft's specific vulnerability to intake blockages and to implement procedures for using alternate air when encountering moisture and temperatures below 5° Celsius.