Steering gear malfunction

Initial Report

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.


Library Image courtesy of Shutterstock


All vessels of the fleet equipped with the same system were directed to replace the potentiometer(s) as soon as practicable and their PMS updated to schedule potentiometer replacement every 5 years. All vessels equipped with the same steering control system were directed to post warning notices describing the steps to be followed in the event of a Servo Loop and FB Fail alarm. The company also contacted equipment manufacturers to investigate how their technical letters are circulated, to ensure proper communication in the future.

CHIRP Comment

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

The vessel’s officers and crew should be fully familiar with the system including its emergency operation to ensure a safe and effective response to control the ship’s heading.

Effective communication with the equipment manufacturers to ensure that vessels’ PMS systems are updated with the latest technical information is essential and should be applied to other items of critical equipment.

CHIRP commends both the ship’s staff and the company for their thorough investigation and analysis. Steering gear problems demand a high degree of analysis and in some cases can be beyond the crew’s ability to rectify.

Items of safety critical equipment must be scrutinised for updates to service letters. This should be handled by the company’s technical (maintenance) teams. Updated service letters should be included in the Planned Maintenance System (PMS) so that ship’s staff can easily find them. Just as importantly, staff who are on leave or working on a different type of ship within the same company must also be alerted to these updated service letters.

The replacement of the potentiometers after a certain period is an easy task and one which can be planned for in advance. Risks associated with items of safety equipment which suffer high use need to be assessed for replacement based on their performance. Take early action and do not let equipment fail in service.

When a company takes over a ship with equipment with which they are not familiar, checks must be made with the manufacturers for their latest technical and service letters. Most manufacturers will have this information on their websites. Class can also be consulted. The original equipment maker should be asked, as part of a service contract, to provide regular updates.

CHIRP believes that the maritime industry can learn from the aviation industry’s control, management and procurement of air safety-critical equipment. The CHIRP Maritime Advisory Board (MAB) suggests that it can, and the CHIRP Maritime team has initiated dialogue with their Aviation colleagues on this issue.

CHIRP feels that procuring safety-critical electronic components will become more complex over time, because commercial off the shelf (COTS) electronic equipment is almost invariably neither type-approved nor marine hardened, and moreover has hardware or software obsolescence built in. Therefore, it should be assumed that all safety-critical and/or high use equipment has a limited life expectancy and should be periodically renewed or replaced based on a formal and documented risk assessment.

It is crucial that emergency steering exercises are conducted where failure in any part of the system can be controlled.

The Master and the officers in this case acted professionally in determining causation and set about rectifying the situation and changing reporting procedures for this equipment.

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.




Report Ends………….