Friction testing is a critical element in maintaining helideck safety across offshore installations. With helicopters landing in high-risk environments—often in poor weather and low visibility—it is imperative that the helideck surface provides a consistent and reliable grip to prevent skidding or loss of control.
UK Civil Aviation Authority guidance, through CAP 437, requires all helideck surfaces to meet minimum friction standards to ensure safe landing and take-off. Testing the surface friction regularly allows operators to detect degradation, contamination, or wear that could compromise aircraft performance.
Why Friction Testing Matters
Helideck friction affects a helicopter’s ability to land and remain stable under rotor downwash, especially on wet surfaces. Offshore conditions—salt spray, rain, algae, and oil—can quickly reduce surface friction below safe limits if not actively monitored. Even a slight reduction in grip can lead to unsafe operations, particularly in emergency landings or high sea states.
By testing the deck regularly and maintaining it within specified parameters, operators ensure compliance with regulatory standards and mitigate the risk of accidents.
Friction Testing Methodology
Friction testing on helidecks involves measuring the coefficient of friction (μ) between a braked test wheel and the helideck surface. This is typically done using equipment designed to simulate a helicopter tyre under realistic operating conditions. The industry standard approach involves testing the deck under wet conditions, using equipment capable of controlled water application.
Approved Testing Method: Braked-Wheel Friction Testing
The only method currently approved under CAP 437 involves a braked-wheel tester, such as the Micro GripTester. This equipment features a small wheel made from aircraft tyre material, which is braked at a controlled rate while being pushed or driven across the deck surface. Friction values are continuously recorded across a grid, usually with a resolution of 1 m².
To ensure full coverage, testing is carried out in two perpendicular passes across the helideck. The results are used to generate a friction map, which identifies any areas falling below the required thresholds.
Equipment Features and Testing Process
Friction testers used for helidecks are typically:
- Self-contained units with water spray systems to ensure consistent wetting of the test surface
- Equipped with digital logging to automatically record and map friction values
- Calibrated to simulate aircraft tyre pressure and material properties
- Designed to provide continuous friction measurement for more accurate data collection
The testing process includes:
- Visual inspection of the helideck surface for contamination or damage
- Pre-wetting the surface using the tester’s spray system or manual means
- Push-testing across two perpendicular axes (e.g. north–south and east–west)
- Data recording and mapping via onboard software
- Analysis and comparison to CAP 437 thresholds
Surface Types and Testing Requirements
Flat Helidecks
Most helidecks are flat steel or aluminium structures finished with non-slip coatings such as grit-blasted surfaces or textured epoxy paint. These are tested in situ with a braked-wheel tester. If results are comfortably above the required minimums, testing may be deferred for up to 24 months. Otherwise, annual testing is required.
After any resurfacing, coating, or repainting, a full friction re-test must be performed to confirm continued compliance.
Profiled Helidecks
Some helidecks use ribbed aluminium planks for improved drainage and weight reduction. These surfaces present unique testing challenges due to directional friction variation. CAP 437 distinguishes between:
- Legacy profiled decks, which may be tested like flat decks if coated with a suitable anti-slip finish
- New installations, which must undergo one-time full-scale testing in controlled conditions, using real helicopter wheels under specific loads and orientations
In all cases, the lowest measured value from testing must meet or exceed the required friction thresholds.
Friction Thresholds
CAP 437 defines the minimum acceptable average friction coefficient (μ) for different parts of the helideck:
- Inside the touchdown/aiming circle:
- Fixed installations: μ ≥ 0.60
- Moving installations (e.g. floating platforms, ships): μ ≥ 0.65
- Outside the touchdown circle (all installations): μ ≥ 0.50
These values apply under wet conditions, as dry tests are not considered representative. The entire deck must meet these criteria with no adjacent 1 m² areas falling below standard.
Remediation and Maintenance
If friction values fall below the minimum threshold, immediate remedial action is required. Suitable methods include:
- Reapplying non-slip coatings
- Grit blasting the surface
- Replacing surface planks (in profiled decks)
- Installing anti-skid nets over the helideck
Following any remedial work, a full re-test must be conducted using approved procedures. Ongoing maintenance, such as cleaning bird droppings, removing oil residue, and repainting worn markings, also contributes significantly to sustaining friction performance.
est Frequency and Recordkeeping
Friction testing should be conducted:
- Annually as a minimum for most helidecks
- Biannually, if the last test results exceeded the minimum by a safe margin (typically μ +0.1 or more)
- Immediately after any resurfacing or significant maintenance
All results should be documented and stored with the helideck safety management system. Operators should ensure that test certificates include:
- Date of test
- Name and model of equipment used
- Calibration status
- Environmental conditions (e.g. temperature, humidity)
- Detailed friction map and pass/fail status
Conclusion
Friction testing is a non-negotiable component of helideck safety management. By adhering to CAP 437 standards and using approved testing equipment and methods, operators can ensure their helideck remains compliant, safe, and ready for operations at all times.
A robust testing regime—backed by proactive maintenance and accurate recordkeeping—ensures that every helicopter landing is as safe as possible, even under the most challenging offshore conditions.