Lessons learned: Steering gear system malfunctions could result in serious consequences

The case

As a container ship was conducting outbound pilotage, the bridge team noticed a delay in response of the steering gear. At the same time, they noticed an alarm indicating “EMERGENCY – XX, SERVO LOOP”. The steering gear was in manual mode operated by Follow-Up (FU) No. 1 and No. 2 system control units.

The steering gear was immediately switched to FU No. 2 mode and the Master immediately initiated the emergency response procedures. The crew were instructed to stand by in the steering gear room for emergency steering if this was necessary.

In the event this not required, and the vessel completed its outbound pilotage without further incident.

The vessel continued her passage to the next port of call. No malfunctions occurred when the system was operating in auto mode in open sea, however, when in hand mode the crew noted that the fault intermittently re-occurred but on each occasion resolved when the system was changed from FU No. 1 to FU No. 2.

While on passage, some remote troubleshooting was carried out by the system’s manufacturer but was not successful, so a qualified technician attended the vessel at the next port of call. The cause was found and rectified.

In the meantime, a risk assessment carried out and the necessary risk control measures had been identified and implemented with the aim of always ensuring safe navigation.

The investigation concluded that the incident was caused by equipment that had become defective through wear and tear. The initial response by the crew minimised the immediate risks to navigational safety, and the prompt action by the company’s technical managers quickly resolved the engineering issues identified. In particular it noted that:

• the steering gear system inspections and tests were carried out in accordance with the company’s procedures and instructions and the vessel’s PMS. There was no malfunction noticed during these tests.
• the malfunction was investigated by a service engineer who identified the cause as the potentiometers of the autopilot system. However, spare potentiometers were not available at the port.
• the malfunction was further investigated by the maker’s service engineer who reconfirmed that the issue was due to an inoperative potentiometer of the auto pilot system control units resulting in a lost signal and alarm. The potentiometers were replaced, and the proper operation restored.
• there was no requirement in the maker’s system manual for replacement of the malfunctioning potentiometers. During the vessel’s special surveys, the system was inspected by qualified technicians and no issue had been raised in respect to the condition of the potentiometers. However, during the investigation it was identified that the maker had issued a technical letter the previous year, which recommend periodical replacement of the potentiometers every five years.
• the subject technical letter was never received in the company.
• there was no document to indicate that the potentiometer had been replaced since the ship’s construction in 2007
• there was no history of any previous malfunction of the system on the vessel nor on any other vessels in the fleet using the same system.

Steering gear system malfunctions during navigation in restricted waters could result in serious consequences for the ship.

…CHIRP concluded.

Human factors relating to this report

Knowledge – Officers of the watch should actively find out how the machinery and control systems that they operate work and develop a sound understanding of their failure and reversionary modes.

Situational Awareness – Actively seek input from others. What have I missed?

Complacency – Never assume all is ok. Always be alert. If it can go wrong, at some point it probably will.