Date: 05 February, 1987
Operator: Gold Coast Air ltd.
Aircraft registration: ZK-KWI
Aircraft type: Piper PA23-250 Aztec
Location: 7nm south-east of Wellington International Airport [WLG], New Zealand
Fatalities: 3 of 3
Relevant weather conditions: Night-time, SCT CU 1800ft
Accident type: controlled flight into terrain
Primary causes: Pilot error, perceptual errors.
The following is a human factors analysis of the crash of ZK-KWI; factual information of the sequence of events is drawn primarily from the official accident report composed by the New Zealand Office of Air Accidents Investigation (19881).
Sequence of events
The pilot of ZK-KWI was asked on short notice to conduct a charter flight from Paraparaumu [PPQ] to Christchurch [CHC], and while initially reluctant, he finally agreed to make the trip. The pilot was not current either for carrying passengers at night, or to fly IFR, and had consumed alcohol shortly beforehand, but made the trip regardless. At 2249 local time, ZK-KWI departed WLG for PPQ on an IFR flight plan and arrived 14 minutes later at 2303. After the charterer boarded the aircraft, ZK-KWI departed for CHC at 2317.
KWI departed PPQ for CHC at 2317, but just 10 minutes into the flight while the aircraft was overhead Porirua at 8000 ft, the pilot radioed Wellington ATC reporting that “We've got a bit of a problem”, and requested to divert to WLG rather than continue to CHC. ATC asked if emergency services were required, to which the pilot replied “No, it's not that immediate”.
Two minutes later at 2329, the pilot requested and received a visual approach to runway 34. Five minutes later, at 2334, ATC noticed that the aircraft's position did not correspond with a visual approach to runway 34, and in fact was headed away from the airport. As a result, ATC asked the pilot “Do you intend to go further south or will you be coming back to the field shortly?”, to which he replied “Negative, we're doing a left hand turn this time. We're remaining 2000 (feet) at this stage”. A minute later, at 2335, another controller asked “What's the situation?”, and the pilot advised that “It's not major but it's not good enough to continue either … It's just the right hand prop control”.
As the aircraft was severely off course by now, ATC then said “How much further south are you going to go?”, and the pilot said “We're inbound this time”. This was the last transmission received from KWI. The aircraft had over four hours of fuel remaining at the time of the accident, and as a result, a searching light aircraft spotted an intense fire in the Rimutaka ranges about thirty minutes later.
Subsequent investigation identified several factors that suggested this was a CFIT accident. Although the pilot had reported “a bit of a problem”, later clarified as “the right hand prop control”, the aircraft was determined to be in an airworthy condition, and both engines were confirmed to be operating. The right hand prop control would not have affected the pilot's ability to control his aircraft, and there were no communications from the pilot indicating either an emergency, or awareness of his proximity to the hills.
Pilot's alcohol level
Due to the post-impact fire the bodies were considerably damaged, however a deep tissue sample revealed that the pilot had a significant quantity of alcohol in his system at the time of the accident. Furthermore, when the pilot began his approach from 8000 ft, the effects of the alcohol would have almost doubled, due to the rarefied air at that altitude. The pilot had consumed alcohol prior to the flight because he was only asked to fly at short notice; however, he should have declined to make the flight.
The aircraft was off course by such a large degree that it is almost certain the pilot was experiencing a visual illusion that completely disorientated him. One strong possibility is that the pilot was experiencing the 'black hole effect', where viewing distant lights over a dark and consistent foreground can cause the pilot to think the aircraft is at a higher altitude than is actually the case. As a result, it would have been easy for the pilot to become unsure of his position, which is very dangerous at night and in the hilly terrain surrounding Wellington Airport. Local conditions, particularly the water around the airport and the lights of Seatoun and Karaka Bay could have created this illusion.
Pilot's decision making
The pilot should have used the IMSAFE mnemonic, or another similar self-evaluation tool to assess his ability to conduct the flight safely. The fact that he conducted the flight after consuming alcohol and without proper currency requirements being met showed a serious hazardous attitude of invulnerability, and poor decision making skills.
The pilot's lack of currency and alcohol content greatly increased his susceptibility to visual illusions. Visual flight in darkness is more hazardous than in daylight due to the many visual illusion that can deceive pilots. While it cannot be stated as fact, the pilot's actions in flying away from WLG and into the hillside can only really be explained by a visual illusion which completely disorientated the pilot and destroyed his situational awareness.
The pilot's susceptibility to 'the black hole effect' was considerably increased by the alcohol in his system and lack of currency, and the combination of the two rapidly lead to total disorientation and loss of situational awareness. It is clear that this CFIT accident was caused by a perceptual error, facilitated by poor judgement in conducting the flight while not fit or current to do so.