Introduction
The UK Civil Aviation Authority (CAA) released Revision 9c of CAP 437: Standards for Offshore Helicopter Landing Areas in February 2023. This revision refines several requirements for Helideck Monitoring Systems (HMS), weather sensors, data display, and alerting logic. This page summarises the core updates from Rev. 9c, with a focus on measurable parameters, software logic, and data handling expectations relevant to helideck operations.
CAP 437 Rev. 9b vs Rev. 9c – Key Differences
Here is a comparison table outlining the key differences between CAP 437 Rev. 9b and Rev. 9c related to Helideck Monitoring Systems and weather data requirements:
| Topic | Rev. 9b | Rev. 9c (February 2023) |
|---|---|---|
| Sampling Rates | Motion: 2HzWind: 4Hz | No change |
| Update Rate | Minimum 0.1 Hz | No change |
| SHR Landing Status Logic | SHR logic applied but rounding method unspecified | Requires use of rounded-up values to determine landing status |
| Declination Handling | May be applied manually | Declination must be automatically calculated and applied |
| Marked Discontinuity (MD) | Not explicitly required on HMS display | MD must be visibly presented in the compass rose display |
| Anemometer Switching | Dual anemometers recommended in some configurations | Automatic switching required when a secondary is available |
| Helicopter Type Defaults | Defaults to Category A often implicit | Category A helicopter must be explicitly applied by default at start-up and in pre-landing mode |
| Day/Night Status | Operator input common | Automatic detection required; system must default to night if undetermined |
| Trend Presentation | Trends required for key parameters | Now mandates 20-minute max values and limit lines for Pitch, Roll, Inclination, and SHR |
| Touchdown Heading Alerts | Alerts on invalid data entry recommended | Mandatory alerts if heading input will cause red/amber RWD status |
| Vessel/Helicopter Δ-Heading | Highlighting optional | Numerical and plot highlighting required for large heading or wind direction changes |
| Repeater Light Control | Testing available | Test function must be inhibited during wind or motion exceedance |
| Sensor Faults | General fault indicators required | Specific requirements for excluding faulty data from buffers and flagging missing data (e.g. greying out parameters) |
| Vessel Categories | General categorisation | Category 1 subdivided into “Cat 1 Semi-Sub” and “Cat 1 Other” |
| Helicopter Categories | Based on older type classification | Updated nomenclature reflecting industry changes |
| Screenshot Sharing | Display transmission methods vary | Streamlined screen capture must be available for sending HMS data to flight crew |
| Training Material Approval | Good practice | Formal review and acceptance of training material now required by national aviation authority (e.g. CAA) |
Note on Compliance and Implementation
CAP 437 compliance requires correct installation, configuration, and operator training in line with the specifications of Rev. 9c. Each helideck installation is subject to review by the relevant aviation authority (e.g. HCA in the UK sector) as part of Site Acceptance Testing (SAT).
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