Airwork Flight 23 was a cargo flight between Auckland International Airport and Blenheim Airport that disintegrated on May 2, 2005. May 2 is the 122nd day of the year in the Gregorian calendar (123rd in leap years). ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... Stratford originally meant ford in a Roman street and is the name of several places. ... Airwork is an airline based in Auckland, New Zealand. ... Airwork is an airline based in Auckland, New Zealand. ... Auckland International Airport (IATA: AKL, ICAO: NZAA) is the largest and busiest international airport in New Zealand. ... May 2 is the 122nd day of the year in the Gregorian calendar (123rd in leap years). ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...

History of Flight

The aircraft was scheduled for take-off at 21:00 but it was delayed while cargo was being loaded. During the delay the pilots ordered an extra 570 litres (about 1000 pounds (lb) or 450 kg) of fuel and told the refueler to put all the fuel in the left wing fuel tank, instead of splitting the fuel exactly between the two tanks as was company procedure. The flight eventually took off at 21:36.

Immediatly take-off the autopilot was engaged and it controlled the aircraft during it's climb to flight level 220. The aircraft continued at full power instead of cruise setting to make up for lost time for the next fifteen minutes. The flight subsequently powered down to cruise power and the captain noticed fuel imbalance on the plane. The aircraft initiated crassflow procedures. Shortly after, at 22:13, the plane entered a spiral descent and broke up, killing both pilots. A simple detachable autopilot on a sailboat. ...

Investigation

The accident was investigated by the New Zealand Transport Accident Investigation Commission. It found that when the captain noted fuel imbalance, he said, "We'll just open the crossflow again ..sit on left ball and trim it accordingly". he repeated the instruction 5 times in the next ninteen seconds, to which the co-pilot replied "I was being a bit cautious". The captain said "Don't be cautious mate, it'll do it good".

This resulted in the plane being flown at a large sideslip angle whilst still under autopilot control, by means of the rudder trim mechanism. 47 seconds after the crossflow was opened, the captain said, "Doesn't like that one mate.. you'd better grab it." One second later they recieved a "Bank Angle" warning, followed by a warning chime that was presumably a warning they were straying from their correct altitude.

The investigation came to the conclusion that this was due to the autopilot disengaging, probably due to a servo reaching it's torque limit. This meant that there was no compensation aplied for the rudder trim imput, and the plane entered a roll and steep descent, disintegrating around flight level 199. The investigation found conditions of nighttime low clould played a factor in preventing the pilots realising sooner.

Aftermath

The following improvements were implemented as a result:

• On 30 May 2005, the operator issued a Notice to Pilots advising that forthwith the SOP was to give the refueller the volume of fuel to be put into each wing tank to achieve a balanced load prior to engine start, in accordance with the Pre-Start checklist, Metro Training Manual and AFM.
• On 30 June 2006 the operator amended the Metro checklist to add to the Line-up and Approach checklists the item "crossflow closed".
• On 4 July 2006 the operator amended the autopilot Standard Operating Procedures section of the company Metro Training Manual to include two cautions on the use of the fuel crossflow switch.
• On 27 February 2006 the TAIC recommended to the Director of Civil Aviation to amend the AFM, in concert with the U.S. FAA, to include a limitation and caution that the autopilot and yaw damper must be disconnected while in-flight fuel balancing is done.

References

• NTSB Report
• ASN Report