Sikorsky S-61N touches water during approach near Den Helder

Casualties unknown • Inadvertent loss of altitude during approach, Sikorsky S-61N, Waddenzee, NL

A helicopter experienced an unplanned loss of altitude and struck the surface of the Waddenzee during an instrument approach due to unnoticed airspeed decay.

What happened

On 30 November 2004, a Sikorsky S-61N helicopter, registration PH-NZG, was performing a return flight from an offshore platform to Den Helder Airport. The aircraft was carrying three crew members and twelve passengers. During the approach over the Waddenzee, the helicopter's airspeed began to decrease gradually. Because the crew did not notice the reduction in speed, they did not compensate with additional power. As the aircraft flew through clouds, the loss of forward momentum led to an increasing rate of descent. After approximately 20 seconds, the pilot in command identified the speed drop and intervened to arrest the descent; however, the aircraft had already made contact with the water. The helicopter was able to regain altitude immediately after the impact and completed a safe landing at the airport. There were no injuries and no significant damage to the aircraft.

The investigation

The investigation examined the flight profiles, crew performance, and organizational safety management. Investigators analyzed the flight data and cockpit voice recordings to reconstruct the sequence of events. The inquiry looked into the technical performance of the Automatic Flight Control System (AFCS) and the crew's adherence to standard operating procedures regarding monitoring and communication. Furthermore, the investigation reviewed the operator's training programs, pilot scheduling, and the effectiveness of their Crew Resource Management (CRM) implementation.

Probable cause

The primary cause was a failure in crew monitoring, where a gradual reduction in airspeed went unnoticed for nearly 20 seconds, leading to a loss of lift and altitude. This was compounded by organizational factors, including inadequate oversight of training effectiveness and potential fatigue due to scheduling.

Frequently asked questions

What happened in the null aircraft accident near Inadvertent loss of altitude during approach, Sikorsky S-61N, Waddenzee, NL?

A helicopter experienced an unplanned loss of altitude and struck the surface of the Waddenzee during an instrument approach due to unnoticed airspeed decay.

What aircraft was involved and where did it happen?

The accident on null involved a aircraft, registration S-61N, at Inadvertent loss of altitude during approach, Sikorsky S-61N, Waddenzee, NL.

What was the probable cause of the accident?

The primary cause was a failure in crew monitoring, where a gradual reduction in airspeed went unnoticed for nearly 20 seconds, leading to a loss of lift and altitude. This was compounded by organizational factors, including inadequate oversight of training effectiveness and potential fatigue due to scheduling.

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