Investigation Summary
The accident occurred during a crew training session focused on touch-and-go landings and engine failures after V1. Captain Donal McLachlan, acting as instructor, was seated in the right seat while trainee First Officer Brian Ruffell occupied the left seat. As the aircraft reached V1 speed, McLachlan attempted to simulate a failure of the number four engine by rapidly retarding its thrust lever. However, a design characteristic of the DC-8 thrust levers allowed the reverse thrust lever to rise and engage the reverse idle detent if the main lever was moved rearward with sufficient speed and force. This resulted in the number four engine deploying its thrust reverser instead of simply idling. The resulting drag increased the minimum control speed (Vmca) from 113 knots to 141 knots, which was significantly higher than the aircraft's rotation speed (Vr) of 118 knots. Consequently, when the aircraft lifted off, it was below the speed required to maintain directional control against the reverse thrust. The aircraft entered an uncontrollable roll and yaw to the right, striking the ground wing-tip first before cartwheeling and breaking apart.
Final Conclusions
The Accidents Investigation Branch (AIB) concluded that the primary cause was the inadvertent engagement of reverse thrust during a simulated engine failure. The investigation highlighted a flaw in the cockpit ergonomics where rapid rearward movement of the power lever could trigger the thrust brake lever via inertia. The AIB issued Aircraft Accident Report No. 1647, which determined that once the reverse thrust was engaged at that critical phase of flight, the aircraft became aerodynamically uncontrollable at the speeds being flown. Although the crew eventually recognized and eliminated the reverse thrust, the aircraft lacked the altitude and time necessary to recover.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Instructor pilot Donal McLachlan, seated in right seat. Fatality.
First Officer
Trainee pilot Brian Ruffell, seated in left seat. Survived.
Flight Engineer
Gordon Tonkin. Fatality.
Systems & Failure Modes
Thrust Reversers
Mechanical systems on the JT3D engines that redirect thrust forward to decelerate the aircraft; on the DC-8, these were controlled by levers attached to the main thrust levers.
Thrust Levers
The cockpit controls for engine power; a design flaw allowed the reverse idle detent to be engaged by inertia if the main lever was pulled back rapidly.
Interesting Facts
- 01The aircraft was a Douglas DC-8-52, MSN 45751/231, manufactured in 1965.
- 02The inadvertent deployment of reverse thrust on the number four engine increased the minimum control speed (Vmca) from 113 knots to 141 knots.
- 03The aircraft's rotation speed (Vr) was 118 knots, meaning it was below controllable speed the moment it lifted off.
- 04Witnesses at the airport reported seeing the fan cascade doors open on the number four engine, a clear sign of reverse thrust deployment.
- 05The Accidents Investigation Branch (AIB) determined that rapid rearward movement of the thrust lever could cause the thrust brake lever to rise due to inertia.
- 06The crash was the first fatal accident in the history of Air New Zealand.
Safety Actions & Advisories
Douglas Aircraft Company Notice
Within three hours of discovering the lever flaw, the AIB notified Douglas, who subsequently issued notices to all DC-8 operators regarding the risk of inadvertent reverse thrust deployment during rapid power reduction.
Mechanical Intervention Recommendation
The AIB final report called for a mechanical modification to the thrust lever assembly to prevent the thrust brake lever from rising due to inertia.
Known Controversies & Unanswered Questions
Initial Dispute Over Cause
Reference ↗Following the crash, there was significant internal tension at Air New Zealand regarding the cause. While the official investigation focused on the mechanical-inertial flaw of the thrust levers, some within the airline initially questioned if the instructor had intentionally engaged reverse thrust to challenge the trainee, a claim that was ultimately dismissed by the physical evidence and subsequent testing.