Marine Helicopter Operations and Helidecks

Ship helicopter operations sit at the intersection of two demanding regulatory regimes: maritime and aviation. A vessel fitted with a helideck is simultaneously a ship under the International Maritime Organization’s SOLAS Convention and a ground facility under national aviation authority rules. Getting those two frameworks to agree on fire protection, structural loading, lighting, and personnel qualifications requires a level of cross-discipline precision that catches owners and operators out repeatedly. This article covers the engineering and regulatory detail that practitioners actually need: the D-value geometry from CAP 437, the SOLAS Regulation 18 firefighting mandate, the Deck Integrated Foam Fighting System (DIFFS) performance standard, the Helideck Monitoring System (HMS) outputs, HLO training, and the distinction between a helideck and a winch-only transfer area.

The companion calculator for helideck obstruction clearance geometry is at /calculators/offshore-helideck-clear-of-obstructions and the operations parameter tool at /calculators/offshore-helicopter-operations.

Regulatory framework

The regulatory stack governing a commercial ship helideck has four layers.

SOLAS Chapter II-2 Regulation 18 is the IMO instrument. It applies to all ships on international voyages and divides requirements into three tiers: ships carrying more than 36 passengers (full helideck), ships with a helicopter landing area (the aircraft can land but it is not a full offshore helideck), and ships with a helicopter transfer area (winch-only; the aircraft does not land). Regulation 18 specifies structural strength, fire protection including DIFFS, foam application rates, firefighting agent quantities, lighting, and rescue equipment. Its 2020 consolidated form in the 1974 SOLAS Protocol applies to new-builds from 2002 and is also expected of existing tonnage on a best-practicable basis through port-state control.

IMO MSC.1/Circ.1431 (2012), titled Guidelines for Design and Approval of Fixed Water-Based Fire-Fighting Systems for Helicopter Landing Areas, supplements Regulation 18. It gives specific engineering guidance on water-based alternatives to foam (water mist systems rated at 20 litres per square metre per minute) and on commissioning tests. Flag administrations may approve a water mist DIFFS under Circular 1431 in lieu of the foam system.

UK CAA CAP 437, now at Edition 9 (2021 revision with subsequent amendments), is the de facto global standard for offshore helidecks. Although it is a UK document, CAP 437 is cross-referenced in Norwegian CAA regulations, accepted by most major classification societies (DNV, Lloyd’s Register, ABS, Bureau Veritas, ClassNK), and required by major oil operators (Shell, BP, TotalEnergies, Equinor) for their charter specifications. CAP 437 covers the D-value, the t-value, obstacle-free sectors, surface friction, lighting standards (including the perimeter “dollar” arrangement), the Helideck Monitoring System, and firefighting requirements in detail that exceeds SOLAS for anything beyond the smallest landing areas.

The ICS Guide to Helicopter/Ship Operations (4th Edition, International Chamber of Shipping) translates those regulatory obligations into practical bridge-level and operations-room procedures for merchant ships, covering HOLD preparation, communication protocols, medical transfer, and cargo sling work.

The IMO MODU Code 2009 (MSC.266(84)) adds Chapter 7 specifically for mobile offshore drilling units. MODUs typically run far more demanding operations than merchant ship helidecks and Chapter 7 cross-references CAP 437 for most of the geometric and firefighting requirements while adding MODU-specific considerations around crane clearances, flare booms, and emergency evacuation capacity.

Helideck vs winch-only transfer area

The single most consequential design decision is whether the aircraft is allowed to land.

A HOSP (Helicopter Offshore SAR Procedures) winch area on a merchant ship allows crew medical evacuation or search-and-rescue insertion without the ship needing a full helideck. The distinction matters economically: a full helideck on a medium tanker adds roughly 15 to 25 tonnes of structural steel, a dedicated fire pump, foam storage, perimeter lighting cable runs, and a DIFFS reticulation system. Operators sometimes accept the winch-only option when the vessel is not required to carry offshore installation workers.

The D-value and landing-area geometry

Every dimensional requirement in CAP 437 derives from the D-value, defined as the overall length of the helicopter from nose to tail-rotor tip (or to any other extremity that protrudes furthest) measured with rotor blades folded if applicable.

For common types operating offshore, the D-values are: Sikorsky S-92 (D = 20.88 m), Leonardo AW139 (D = 16.66 m), Airbus H175 (D = 18.53 m), Airbus H225 Super Puma (D = 19.50 m), Sikorsky S-76D (D = 16.00 m). The helideck must be approved for a specific maximum D-value helicopter type.

TLOF (Touchdown and Liftoff Area) must have a diameter of at least 1D and must be circular or have a minimum inscribed circle of 1D. For the S-92 that is 20.88 m minimum. CAP 437 Edition 9 tightened the surface friction requirement: the static friction coefficient of the TLOF surface must be at least 0.65 (wet) measured with a portable friction tester, and the dynamic value at 0.64 km/h slip speed must be at least 0.60. Below those thresholds the helideck is unserviceable.

FATO (Final Approach and Takeoff Area) on offshore helidecks is typically coincident with the TLOF for structures with a single landing circle. On installations with room for a separate FATO it extends 3 m beyond the TLOF.

Obstacle-free sectors: CAP 437 requires an obstacle-free sector spanning at least 210 degrees around the TLOF at its level, with objects in the remaining 150 degrees limited to a 5-degree elevation above the TLOF plane within 0.62D, rising to a height of 25 m at 0.83D. The clear 210-degree arc is the primary approach direction band; helicopter operators must confirm the vessel’s superstructure, crane jibs, and exhaust stacks do not intrude.

The t-value (touchdown point tolerance) is the horizontal distance from the TLOF center at which the helicopter manufacturer certifies the aircraft can touch down safely under the helideck’s designated motion environment. CAP 437 uses the t-value to verify whether a given vessel motion envelope (roll, pitch, heave, combined) stays within the helicopter type’s certified limits. It is not a single universal number: the S-92 has a different t-value to the AW139, and the master must check the current vessel HMS data against the applicable aircraft’s performance sheet before approving operations.

The “dollar circle” is the informal name for the perimeter marking system: a white painted circle at the edge of the TLOF, with a broken-line perimeter (resembling a dollar sign $ overlaid on a circle in older marking schemes, now standardised as a solid yellow circle with white perimeter lights at 3 m spacing). The yellow circle is 0.83D diameter, inset from the TLOF edge.

Helideck Monitoring System

CAP 437 Appendix A mandates a Helideck Monitoring System (HMS) on offshore installations and on vessels that conduct helicopter operations to offshore installations. The HMS measures and displays in real time:

• Deck inclination (roll and pitch in degrees, combined with an alarm at 3 degrees from the horizontal from CAP 437 limits)
• Heave (vertical acceleration or displacement, alarm limit defined by aircraft type)
• Wind speed and direction at helideck level (accurate to ±0.5 m/s; cup anemometer or ultrasonic; displayed on bridge and at HLO station)
• Helideck air temperature (for helicopter performance calculations)
• Barometric pressure at helideck level

The HMS outputs are transmitted in real time to the helicopter pilot by voice (bridge-to-cockpit) and on some modern installations via data link. The pilot uses roll/pitch and heave data to compute the motion severity rating (MSR) against the helicopter type certificate limits before initiating approach. If MSR exceeds the limit, the approach is aborted. CAP 437 Table A-1 gives the limiting motion spectrum for each major offshore helicopter type; the values are provided by the helicopter OEM and incorporated into the CAP 437 amendment cycle.

An HMS is NOT the same as the vessel’s motion monitoring system for cargo operations. It must be a dedicated calibrated instrument with data logging so that post-incident analysis can confirm what conditions existed at the moment of touchdown.

SOLAS Chapter II-2 Regulation 18 firefighting requirements

Regulation 18 of SOLAS Chapter II-2 (Fire protection, fire detection, and fire extinction) sets the minimum firefighting standard for ships with helicopter facilities. The precise requirements depend on the category of facility.

For ships carrying more than 36 passengers with a helideck (Reg 18.6):

• A fixed foam firefighting system covering the TLOF, capable of delivering foam solution at not less than 6 litres per square metre per minute over the entire TLOF area simultaneously.
• The system must be capable of operating for at least 5 minutes at the rated application rate.
• Dry powder extinguishing units with a minimum aggregate capacity of 45 kg, positioned within 10 m of the TLOF edge on two sides, operable without entering the fire zone.
• Two CO2 extinguishers of at least 5 kg each, or equivalent halon-replacement agent, for wheel-bay and avionics-bay fires.
• A firefighting crew of at least two persons in full protective clothing (fire proximity suit, SCBA) standing by during all helicopter operations.

For ships with helicopter landing areas (not qualifying as full passenger-ship helideck): Regulation 18.7 requires portable foam-making equipment delivering at least 500 litres per minute of foam solution, plus dry powder units totalling 45 kg minimum. The portable system must be capable of covering the landing area within 30 seconds of crew deployment.

For ships with winch/transfer areas only: Regulation 18.8 requires portable equipment capable of generating foam or equivalent equivalent, positioned ready for immediate use, plus dry powder units.

The IMO MSC.1/Circ.1431 water-mist alternative applies only if the flag state accepts the deviation and the system delivers at least 20 l/m²/min over the TLOF for 5 minutes with automatic actuation.

DIFFS: deck-integrated foam fighting system

DIFFS is the term used in CAP 437 and adopted by the offshore industry for the fixed foam application system that satisfies SOLAS Regulation 18.6. A properly engineered DIFFS has five sub-systems.

Foam concentrate storage and proportioning. AFFF (Aqueous Film Forming Foam) at 3% or 6% concentration has been the offshore standard since the 1970s. Since 2020, the offshore industry has been transitioning to fluorine-free foam (F3 or FFFP) driven by PFAS environmental regulation. The proportioning system (bladder tank, around-the-pump proportioner, or in-line inductor) must deliver concentrate within ±0.5% of rated ratio under all supply pressure conditions. The foam agent tank must hold enough concentrate for the 5-minute design duration plus a 100% reserve, for a total of 10 minutes of agent.

Fixed monitors. CAP 437 requires at least two monitors positioned on opposite sides of the helideck, each capable of covering the entire TLOF with a solid foam blanket without repositioning. Remote-operated or manual-override monitors are acceptable. Throw distance at rated flow must exceed the TLOF radius plus 3 m. Monitors with oscillating nozzles that sweep the deck are increasingly common on drillships where the helideck is large (D > 20 m).

Hose reels. At least two reels of 38 mm hose, each 30 m long, must be mounted within 3 m of the TLOF perimeter, stored in weathertight cabinets, and capable of delivering foam solution at 250 litres per minute at the nozzle. The reels supplement monitor coverage for wheel-bay fires and aircraft belly fires that monitors cannot reach.

Fire pump and water supply. A dedicated foam system pump drawing directly from the sea or from a header charged by the vessel’s general fire pump must maintain rated delivery pressure against monitor demand. The pump must start automatically on system activation and be capable of running dry for 15 seconds without damage. On vessels where the main fire pump is shared, a dedicated start-before-demand interlock ensures the helideck system has priority.

Detection and auto-actuation. A fusible-link or heat detector network on the TLOF triggers automatic system release. Manual push buttons on at least two sides of the helideck provide override. CAP 437 requires actuation to reach full foam discharge within 30 seconds of signal.

The commissioning performance test for a new DIFFS requires demonstration of 6 l/m²/min over the full TLOF simultaneously, measured with collection trays, not just monitor throw-range calculations. Classification society surveyors (DNV, LR, ABS) witness the test and hold the certificate of compliance.

Lighting and markings

Night operations and instrument-meteorological-conditions approaches require a lighting fit well beyond the basic SOLAS requirement.

Perimeter lights: Green lights at 3 m spacing around the full TLOF perimeter, flush-mounted or recessed to avoid obstruction. CAP 437 specifies intensity of not less than 10 candela in the elevation angle range 0 to 10 degrees above horizontal and 360 degrees in azimuth. On vessels with a helideck diameter above 1D by more than 10%, additional lights at the FATO edge are required.

Helideck identification “H”: A yellow H centered on the TLOF, conforming to CAP 437 Figure 4.2, with each stroke 1.5 m wide. The H is back-lit on permanently installed structures; on ship helidecks retroreflective paint is acceptable for the static marking, supplemented by floodlighting. Some operators also paint the maximum D-value helicopter designation (e.g., “22”) in the upper sector of the H marking to alert pilots of the approved type limit at a glance.

Floodlights: At least three floodlights, evenly spaced around the helideck perimeter, each rated minimum 200 W (tungsten-halogen equivalent), aimed to illuminate the full TLOF without creating glare sectors in the pilot’s final approach path.

Obstruction lights: Red lights at 25 candela minimum on any structure within 210 m of the TLOF that exceeds 45 m above sea level. On FPSOs with flare towers and derricks within this radius, obstacle lighting becomes complex; the specific pattern is agreed with the aviation authority and documented in the HOLD.

Wind direction indicator: A lighted wind sock or equivalent, positioned at TLOF edge height, visible from the approach direction. On offshore installations a second sock on the downwind side reduces shadowing.

The Helicopter Landing Officer and crew

CAP 437 and the ICS Guide are explicit that a trained Helicopter Landing Officer (HLO) must be on duty and physically present on or adjacent to the helideck for every landing and takeoff. The HLO’s authority can override the captain’s permission to land if the HLO judges conditions unsafe. That authority structure is unusual in the maritime context and worth noting: the HLO can say no even if the bridge has granted clearance.

HLO certification. OPITO (Offshore Petroleum Industry Training Organization) administers the globally recognised HLO standard. The initial course (OPITO standard 7015) runs 4 days and covers: HOLD reading, CAP 437 requirements, firefighting procedures, helicopter recognition, crew duties, communications, and simulation exercises. Refresher is required every 2 years (standard 7016, 2 days). The HLO certificate is not transferable: if the designated HLO is unavailable, operations wait.

Helideck crew. A minimum of two personnel (HLO plus at least one Helideck Crew Member, HCM) must be standing by in protective clothing during all landing operations. The HCM holds an OPITO Helideck Crew Member certificate (standard 7017). Duties split: HLO manages communications and signals; HCM stands by with dry-powder extinguisher and monitors aircraft approach.

Communication protocol. The ICS Guide mandates that the HLO maintains voice contact with the pilot from 5 nautical miles out through to engine shutdown. The standard check-call at 2 nm includes: helideck condition (serviceable/unserviceable), wind speed and direction from HMS, current roll and pitch, visibility at deck level, any operational restrictions, and confirmation of the helicopter type’s approval in the HOLD.

HUET. Passengers and crew travelling by helicopter to or from an offshore installation must hold a current OPITO Helicopter Underwater Escape Training (HUET) certificate (standard 0151). The 1-day course involves simulated ditching in a pool with capsizing cabin exercises. Certificate validity is 4 years; recurrency is annual Compressed Air Emergency Breathing System (CAEBS) familiarization.

Structural design loads

The helideck structure must carry three categories of load simultaneously.

Aircraft load. The design hard-landing load is defined as the helicopter’s Maximum Take-Off Weight (MTOW) multiplied by a dynamic amplification factor. CAP 437 uses 1.5 x MTOW as the design load for structural sizing. For the S-92 (MTOW 12,020 kg), the design point load is approximately 177 kN concentrated at the main gear footprint (two main wheels, one nose wheel, with specific contact areas defined in the helicopter OEM’s structural interface document). The offshore industry uses this criterion directly; classification societies typically verify it against their own structural codes.

Ship motion loads. A helideck at the top of an accommodation block experiences amplified vertical acceleration. On a DP-equipped FPSO in a 5 m significant wave height (Hs), vertical accelerations at main-deck level of 0.3 g are common; at accommodation-block top they can reach 0.5 to 0.7 g in the natural pitch period. The helicopter structural load under ship motion is MTOW x (1 + a_v/g) where $a_v$ is the peak vertical acceleration. The structural analysis must confirm this does not govern over the hard-landing load; on vessels with high freeboard in exposed areas it sometimes does.

Environmental loads. Wind load on a parked helicopter is significant. An S-92 with blades spread has a projected area of approximately 340 m²; at a 60 m/s survival wind (typical offshore design), the drag is on the order of 300 kN. Tie-down points must be designed to restrain the aircraft under these loads using a minimum of four tie-down chains rated to 45 kN each, distributed to the aircraft’s designated lashing rings. The helideck surface at tie-down locations must be reinforced inserts capable of taking uplift.

Refueling systems and Jet A-1 handling

Refueling on an offshore vessel requires a dedicated aviation fuel installation meeting DEFSTAN 02-634 (UK) or equivalent.

Fuel storage. Dedicated aviation-grade tanks, completely segregated from ship’s fuel systems, with a capacity typically 20 to 60 m³ for vessels running daily sorties. Tanks are earthed and equipped with high-level alarms. The fuel must be certified Jet A-1 (ASTM D1655 or DEF STAN 91-091) and sampled on arrival, after any top-up, and before each fueling operation.

Fuel quality control. Water content is monitored by Aqua-Glo or equivalent colorimetric test. The limit is 30 ppm free water; above this the fuel is quarantined. Particulate filtration downstream of the storage tank must meet EI 1583 (Aviation Turbine Fuel Filtration Equipment); the coalescer/separator element is replaced on differential pressure alarm or after 6 months regardless. A batch record including specific gravity at delivery temperature is maintained for each parcel.

Pressure refueling. Over-wing or pressure (pressure-to-fill) fueling is conducted through a self-sealing coupling (DEF STAN 02-634 type). Flow rate is controlled to avoid excessive pressure: maximum 100 litres per minute for helicopters up to S-92 class. Anti-static bonding is applied before the fuel cap is opened: a dedicated bonding wire from the aircraft designated earth point to the fueling rig. The bonding must precede any fuel connection and remain until the fuel connection is broken.

MODU Code Chapter 7 specifics

Mobile offshore drilling units (drillships, semi-submersibles, jack-ups) carry helidecks that are larger and operationally more intensive than most merchant-ship installations. Chapter 7 of the 2009 MODU Code adds requirements beyond SOLAS Regulation 18.

Size. MODUs typically operate S-92 and AW189 aircraft daily; helideck TLOF diameters of 22 m to 28 m are common on drillships. Chapter 7 requires that the TLOF be sized for the heaviest helicopter approved in the vessel’s operating manual.

Crane clearances. Crane booms must be capable of being lowered below helideck height during helicopter operations. The MODU Code requires a written procedure in the operations manual covering crane position during all helicopter movements. Class surveyors verify this at initial survey.

Emergency evacuation. Chapter 7 recognises that the helideck on a MODU may be the primary means of evacuation for 150+ offshore workers in an emergency. The firefighting capacity is sized accordingly: MODU helidecks typically carry DIFFS rated at twice the SOLAS Regulation 18.6 minimum, plus an additional dry-powder system with aggregate capacity of 250 kg.

Helideck structural survey. Classification society rules (DNV-OS-E401, LR ShipRight procedures) require a helideck structural survey at each Special Survey (every 5 years), including thickness measurement of the deck plate, inspection of the beam flanges at the tie-down insert locations, and a load test with dead weights equivalent to MTOW x 1.5.

Merchant-ship vs offshore installation comparison

The practical difference between a merchant-ship helideck and a full offshore installation helideck is significant.

The notation difference matters for chartering: a vessel with an LR HEL notation has met Lloyd’s Register’s assessment of basic SOLAS compliance; a vessel with HEL+ has additionally met CAP 437 to the satisfaction of LR surveyors. Oil majors typically specify HEL+ or equivalent in charter party fixtures.

Winching and HOSP operations

HOSP (Helicopter Offshore SAR Procedures) covers winching operations that do not require the aircraft to land. The ICS Guide Chapter 8 sets out the protocol for merchant vessels.

Winch area. A 10 m x 10 m clear deck space, free of obstructions above deck level within a 5 m radius, is the minimum specified by the ICS Guide. The area should be marked with an H (non-illuminated is acceptable for daytime use) and bordered by a 1 m wide yellow stripe. Personnel must clear the area to a 15 m radius during winching due to rotor downwash and static discharge.

Static discharge. Before any winch hook or rescue device touches the ship’s deck, it must be grounded. The standard method is to allow the wire to touch the deck (or an earth rod held by crew) before personnel touch the hook. Static charges of several thousand volts can build up on an insulated wire during hover; the discharge through an unprotected hand has caused burns and cardiac events.

Communication. The winch operator in the aircraft and the HLO on deck maintain a continuous intercom or VHF channel. The ICS Guide specifies that the master or officer of the watch hold a separate bridge-to-cockpit channel simultaneously so that vessel heading adjustments can be coordinated if necessary.

Medical transfers. A significant proportion of HOSP operations on merchant vessels are medical evacuations. The ICS Guide requires a stretcher of a type approved for helicopter winching to be carried on board for this purpose, pre-rigged and ready before the aircraft arrives. Crew must be trained in packaging a casualty for helicopter transfer; this is part of STCW Basic Safety Training (STCW VI/1) and is not helicopter-specific.

Ship motion limits and the operating envelope

Every vessel conducting helicopter operations must define motion operating limits in its HOLD (Helicopter Operating Limitations Document).

The HOLD is a vessel-specific document prepared by the ship operator, reviewed by a qualified helideck specialist, and accepted by the applicable aviation authority (NORGANSORG in Norway, the UK CAA for North Sea UK-flagged vessels). Its contents, per the ICS Guide, include:

• Vessel name, IMO number, flag, class certificate reference
• Helideck position and dimensions (TLOF diameter, clear sectors with bearing references)
• Approved helicopter type(s) with D-value and MTOW
• Motion limits for each approved type (roll, pitch, heave, combined MSR)
• HMS sensor positions and calibration certificate references
• Firefighting system description (DIFFS model, foam agent type, application rate test result)
• Crew qualifications required (HLO, HCM certificates held on board)
• Obstruction plot: plan view showing all structures within 210 m of TLOF center with heights
• Lighting schematic and maintenance schedule
• Refueling system data (if fitted)
• Operational procedures: approach, landing, passenger transfer, departure, emergency

The HOLD is a living document: it must be updated whenever the vessel’s superstructure changes, a new helicopter type is approved, or a firefighting system is modified. Vessels operating for oil majors face operator audits where the HOLD currency is verified against the vessel’s physical configuration.

Ship motion and the D-value/t-value interaction

The t-value is the distance from the TLOF nominal center at which the helicopter type can safely touchdown under the vessel’s maximum declared motion, as defined in the helicopter flight manual and confirmed by the OEM’s structural interface document. It is not published in CAP 437 as a single number; each helicopter type’s OEM issues a specific value, and CAP 437 Appendix A requires the HMS to confirm that the vessel motion at the time of landing keeps the expected touchdown scatter within the t-value circle.

For the S-92, the touchdown scatter radius (t-value) is approximately 1.5 m under benign conditions and increases in heavy weather. On a vessel with a 20.88 m TLOF and an HMS reading 3 degrees combined roll/pitch, the pilot and HLO together confirm that the t-value scatter still keeps the aircraft within the TLOF boundary. If not, landing is deferred.

The practical consequence is that in bad weather the TLOF effective operational diameter shrinks from 1D to something smaller. A helideck rated for 1D with no margin becomes marginal in 3-metre significant wave height; a 1.2D TLOF has meaningful operational buffer. Operators making chartering decisions for vessels that will serve offshore installations in the North Sea, GoM, or South China Sea routinely specify 1.1D or 1.2D TLOF to maintain operations in typical operational sea states.

Helideck surface friction and inspection

CAP 437 Section 6 sets friction requirements that are routinely the cause of helideck unserviceability on older vessels.

The TLOF surface must maintain a wet dynamic friction coefficient of at least 0.60 when measured with a GripTester or Saab Friction Tester run at 65 mm/s slip speed. The test is conducted annually and after any surface treatment. Common failures: the deck paint used outside the TLOF bleeds onto the TLOF through weathering; anti-corrosion paint applied during dry-dock has lower friction characteristics than the original grit-impregnated epoxy; the deck plate corrodes unevenly and the rust-converter coating used in repair fails the friction test.

A surface reading below 0.60 requires the helideck to be declared unserviceable until the surface is remediated. On an FPSO on a 5-year dry-dock cycle, maintaining above-threshold friction for the full 5 years requires a specific maintenance plan: grit-blasting and re-application of CAP 437-compliant coating at the 30-month interval, with friction testing at 12-month intervals between.

Emergency response procedures

The ICS Guide Chapter 10 and SOLAS Regulation 18 both address emergency response, and the two accounts are consistent on most points.

Aircraft accident on deck. The HLO calls general alarm and the fire team’s DIFFS activation simultaneously. The priority sequence is: extinguish or contain fire (DIFFS plus dry-powder team); evacuate surviving passengers from the aircraft; establish triage area at the designated muster point (at least 25 m from TLOF). The HLO does not enter the fire zone until either the fire is suppressed or the fire team has confirmed the aircraft is safe.

Ditching within sight of vessel. The master deploys the vessel’s rescue boat if sea state permits, broadcasts a MAYDAY (or MAYDAY relay if the helicopter crew transmitted first), and activates EPIRB if the rescue is going to require SAR authority assistance. The EPIRB emergency position indicating radio beacon must be accessible and satellite-linked to pass accurate position to the SAR coordination center. The vessel’s AIS-SART described in AIS-SART search and rescue transmitter is a secondary tool that search aircraft can home in on.

Fire on deck with aircraft secured. The DIFFS must be capable of activation by the fire team without entering the fire zone. Remote-activation handles at both sides of the TLOF are required by CAP 437. The HLO initiates DIFFS if the fire is fuel-fed (pool fire under fuselage); dry-powder first for engine-bay or wheel-bay fire (do not wash burning fuel over unsealed areas with foam).

Crash without fire. Passenger rescue takes priority; the fire team stands ready but does not spray until fire starts. Pre-activating DIFFS on a non-burning aircraft contaminates the cabin interior, impairs visibility for rescuers, and is counterproductive.

Limitations

Several limitations apply to the material in this article.

The SOLAS Regulation 18 requirements cited here are from the consolidated 1974 SOLAS text as amended through the 2023 amendment cycle. Vessels built before 2002 may be subject to transitional provisions under MSC/Circ.895 and flag-state equivalency letters; their HOLD should document any such derogation.

CAP 437 Edition 9 applies to UK-registered installations and aircraft registered to UK-regulated operators. Norwegian operations follow BSL E 5-1 of the Norwegian CAA, which references CAP 437 but has some divergent requirements on HMS integration. Operations in the US Gulf of Mexico fall under BSEE Notice to Lessees requirements and USCG Title 33 CFR Part 135, which differ from CAP 437 on friction test method and on foam application rate verification.

The D-values cited for specific helicopter types are drawn from the respective OEM’s flight manuals as available at time of writing. OEMs revise these values when structural modifications affect the airframe geometry; always use the value from the current type certificate documentation.

This article does not constitute engineering design guidance for helideck structural calculations. Structural sizing for a specific vessel must be performed by a qualified naval architect against the relevant class society rules and verified by class survey.

See also

Related calculators

• Offshore Helicopter Operations Calculator
• Offshore Helideck Clear of Obstructions Calculator
• Polar Ice Reconnaissance Helicopter Calculator

Related wiki articles

• Marine Fire Detection and Fixed Fire-Fighting Systems
• SOLAS Chapter II-2: Fire Protection, Detection, and Extinction
• Marine Lifeboats and Survival Craft
• Marine Dynamic Positioning Systems
• FPSO: Floating Production Storage and Offloading
• EPIRB Emergency Position Indicating Radio Beacon
• AIS-SART Search and Rescue Transmitter
• Ship Motions
• Heavy Weather Operations