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Unstable approach leads to NZ runway excursion involving Metro III
16 April 2010

A TAIC New Zealand incident investigation report indicates that an unstable night-time visual approach lead to a Metro III runway excursion at New Plymouth Aerodrome, New Zealand.

On 30 March 2009 at 23:40, a Swearingen SA227AC Metro III air ambulance aeroplane, registered ZK-NSS, took off from Auckland International Airport (AKL/NZAA) on a night flight to New Plymouth Airport (NPL/NZNP) to uplift a patient. On board were 2 pilots and a medical team of 3. The flight was without incident until the approach at New Plymouth.
The pilots carried out a visual approach, although that was generally not permitted by the aeroplane operator at an uncontrolled aerodrome, and without the help of approach slope indicator lights. During the landing checks the right engine did not go to high speed as selected, and the pilots were distracted in trying to find the reason. The base turn was carried out close to the aerodrome and involved a high rate of descent that generated ground proximity warnings. The pilot flying reduced the rate of descent and continued with the approach, rather than carrying out an immediate go-around.
Late on final approach the pilots realised that the aeroplane’s current glide path would result in a landing very close to the runway end. The pilot flying said that he had difficulty controlling the aeroplane when power was increased, which he assumed was caused by the engine speed anomaly. He judged that it was preferable to continue and land rather than to attempt a go-around with an apparent control problem, so he left the power unchanged. The aeroplane landed heavily at the runway end and immediately ran off the side of it. No-one was injured and apart from minor damage to the tyres the aeroplane was undamaged.
The approach was rushed because of the pilots’ decision to commence a visual approach from a point close to the aerodrome. The resultant high rate of descent, together with the distracting engine speed anomaly, led to the ground proximity warnings. The lack of approach slope indicator lights denied the pilots a useful aid for establishing a stable approach. The runway excursion occurred because the pilot flying had a control difficulty and was not in full control of the aeroplane during the landing.
If the pilots had conducted an instrument approach as the operator had required, the approach would likely have been stable and given them more time to deal with the engine speed issue, the cause of which was not determined. Had they applied typical cockpit resource management techniques and the operator’s approach monitoring requirements had been better defined, the unstable approach should have been detected and discontinued. The lack of intervention by the pilot not flying might have been caused by a less-than-optimum trans-cockpit authority gradient.
A few days later, before the aeroplane had been released back to service, a fuel bypass event caused the right engine to run down. Trouble-shooting suggested the Single Red Line interface unit was defective.
Although some defects were found in the unit, they would not have led to a fuel bypass, the cause of which remained undetermined. A fuel bypass was not considered to have occurred at New Plymouth, and the 2 events were likely to have been unrelated.
The Transport Accident Investigation Commission (the Commission) made a safety recommendation to the Director of Civil Aviation regarding delays in the notification of serious incidents to the Civil Aviation Authority and to the Commission.

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