GMDSS & Radio Communication

GMDSS and radio communication servicing

GMDSS and radio communication servicing keeps a ship's distress, urgency and safety communications working when they are needed and ready for the annual radio survey. The Global Maritime Distress and Safety System combines terrestrial radio (VHF, MF and HF with digital selective calling), satellite communications through a recognized mobile satellite service, maritime safety information receivers such as NAVTEX and EGC, and locating devices such as EPIRBs and SARTs.

vslSafety coordinates radio technicians and radio surveyors at the vessel's port to test, repair and document GMDSS installations.

Regulatory requirements and standards

Radiocommunication requirements sit in SOLAS chapter IV. A complete replacement text of chapter IV, adopted by resolution MSC.496(105), entered into force on 1 January 2024 as part of the GMDSS modernisation. It replaced references to Inmarsat with the term recognized mobile satellite service (RMSS), so that both Inmarsat and Iridium services can be used, redefined sea area A3 by reference to the RMSS coverage of the ship earth station carried, and moved the requirements for SARTs and two-way VHF radiotelephones for survival craft from chapter III into chapter IV. IMO circular MSC.1/Circ.1676 allows equipment built to the former performance standards to continue to be installed until 1 January 2028.

SOLAS regulation IV/15 requires the availability of radio equipment to be ensured by duplication of equipment, shore-based maintenance or at-sea electronic maintenance capability. Ships in sea areas A1 and A2 must use at least one of these methods and ships in sea areas A3 and A4 at least two. Resolution A.702(17) gives radio maintenance guidelines for ships in areas A3 and A4. Under SOLAS regulation I/9, the radio installations of cargo ships, including those used in life-saving appliances, are surveyed before the ship enters service, at renewal intervals not exceeding five years, and at a periodical survey within three months before or after each anniversary date of the Cargo Ship Safety Radio Certificate. The survey is carried out by the flag administration, its recognized organization or a radio surveyor authorised by them; repair work is usually done by maker-trained technicians.

Inspection and servicing intervals

Item	Requirement	Interval	Reference
Radio installations (cargo ships)	Periodical survey of the safety radio installation	Within 3 months before or after each certificate anniversary date	SOLAS I/9
Radio installations (cargo ships)	Renewal survey	At intervals not exceeding 5 years	SOLAS I/9
Satellite EPIRB	Annual test and shore-based maintenance	Annual; maintenance at intervals not exceeding 5 years	SOLAS IV/15, MSC.1/Circ.1040/Rev.1
Equipment availability in A3/A4	At least two maintenance methods, often duplication plus a shore-based maintenance agreement	Continuous	SOLAS IV/15, resolution A.702(17)

What the service includes

• Pre-survey check of all GMDSS equipment listed in the Record of Equipment against what is actually fitted
• Transmitter output, frequency and receiver checks on MF/HF and VHF DSC installations using calibrated test equipment
• DSC test calls, verification of the programmed MMSI and ship identity, and position input checks
• Testing of Inmarsat-C, Fleet Safety or Iridium GMDSS terminals, including distress alert test procedures and EGC reception
• NAVTEX receiver checks, message reception and station selection
• Reserve source of energy inspection, battery capacity and charger tests, and automatic changeover checks
• Antenna, feeder, insulator and earthing inspection, with VSWR or impedance measurement where relevant
• Survival craft two-way VHF radios, spare batteries and expiry dates
• Fault finding, board or unit replacement, and software or firmware updates approved by the maker
• Radio log and documentation review, including licence, shore-based maintenance agreement and operator certificates

Equipment types covered

Typical installations include MF/HF DSC transceivers, VHF DSC fixed radios, satellite ship earth stations on Inmarsat or Iridium networks, NAVTEX receivers, EGC receivers, GMDSS consoles and alarm panels, survival craft VHF radios, and the associated batteries, chargers and antennas. Common makers include Furuno, JRC, Sailor (Cobham), Icom, McMurdo and Jotron. Related safety items are covered in our EPIRB and SART servicing page, and ship-wide radio and navigation electronics often share attendance with navigation equipment services.

Common defects and PSC deficiencies

• MF/HF DSC unable to send a test call or with incorrect position data because the GNSS feed has failed
• Reserve batteries with low capacity, poor electrolyte condition or no evidence of regular load testing
• Radio log not kept up to date or daily DSC and battery checks not recorded
• Damaged antennas, corroded connectors or broken insulators causing low output
• Satellite terminal not logged in, wrong ocean region, or distress alert function not tested
• Expired survival craft VHF batteries and missing shore-based maintenance agreement for A3 ships

Certificates and documents you receive

Depending on the scope, the attendance produces a service report listing measured values and actions taken, a radio survey report or test record for the surveyor, battery test records, replacement part details and, where requested, a shore-based maintenance agreement or confirmation of arrangements. Endorsement of the Cargo Ship Safety Radio Certificate is made by the flag administration or its recognized organization, not by the servicing company.

How to prepare the vessel

Have the radio log, Record of Equipment, ship station licence, MMSI and satellite terminal identities, and previous survey report ready. Charge the reserve batteries in advance, make sure the GMDSS operator is available during the attendance, and arrange safe access to the antenna locations on the monkey island. Where a survey is planned, schedule the technician before the surveyor so defects can be cleared first.

Information needed for a quotation

• Vessel name, IMO number, flag, class and sea areas of operation
• Port, berth or anchorage, ETA and ETD
• Scope required, such as pre-survey check, radio survey support, repair or shore-based maintenance agreement
• Maker, model and serial numbers of the GMDSS equipment and a description of any defect
• Date of the last radio survey and certificate anniversary date
• Copies of recent survey reports, PSC deficiencies or error messages

vslSafety coordinates a suitable radio technician or surveyor at the vessel's port and confirms scope, timing and cost before attendance.

Frequently asked questions

How often is a GMDSS radio survey required?

For cargo ships, SOLAS regulation I/9 requires a periodical survey of the radio installation within three months before or after each anniversary date of the Cargo Ship Safety Radio Certificate, and a renewal survey at intervals not exceeding five years. In practice this means an inspection roughly every year. Passenger ships are surveyed under their own certificate regime. The survey is carried out by the flag administration, its recognized organization or an authorised radio surveyor, so check who your flag accepts before booking.

What is a GMDSS shore-based maintenance agreement?

It is a contract with a service organisation that can repair or replace GMDSS equipment in port when it fails. It is one of the three maintenance methods listed in SOLAS regulation IV/15, alongside duplication of equipment and at-sea electronic maintenance. Ships trading in sea areas A3 and A4 must use at least two methods, and most combine duplicated equipment with a shore-based maintenance agreement.

What changed in the GMDSS on 1 January 2024?

A revised SOLAS chapter IV, adopted by resolution MSC.496(105), came into force. Inmarsat-specific wording was replaced by recognized mobile satellite service, allowing Iridium as an alternative, sea area A3 was redefined by satellite coverage, and SART and survival craft VHF requirements moved into chapter IV. Most existing ships did not need new hardware immediately, but documentation, Records of Equipment and operator familiarity should reflect the new text.

Can the crew fix GMDSS faults themselves?

Crew carry out routine daily, weekly and monthly tests and can deal with simple faults such as fuses or loose connections. Repairs to transmitters, receivers or satellite terminals, and any reprogramming of identities, should be done by qualified technicians using approved parts and the maker's procedures. Where the ship relies on at-sea electronic maintenance, the person on board must hold the appropriate qualification accepted by the flag.