EASA CS-26.201 for Operators: Reducing the Risk of Inadequate Tyre Inflation Pressure

Minimum serviceable inflation pressure means a tyre inflation pressure specified by the aeroplane type certificate holder below which damage to the tyre, potentially leading to a tyre failure, may occur. Studies indicate that large transport aircraft tyres can lose up to 5% of their pressure per day in normal operations. At that rate, a tyre could drop below safe limits within just a few days.

Under-inflated tyres are a leading cause of tyre and wheel problems on large airplanes, despite decades of efforts by industry and regulators. Maintaining correct tyre pressure is crucial for safety, as low pressure can damage tyres or even cause them to burst, sometimes affecting other tyres on the same axle. Visual inspections usually cannot detect under-inflated tyres, because the properly inflated tyres carry most of the load. Over-inflated tyres are less common but can still cause wheel damage and loss of pressure if unnoticed. While daily tyre pressure checks have long been recommended by manufacturers, they remain only a recommendation.

Between 2002 and 2016, EASA recorded 848 tyre- and wheel-related events on large airplanes, including 57 accidents, 73 serious incidents, and 718 other incidents, highlighting the ongoing safety risk of incorrect tyre pressure. The numbers speak for themselves.

Following the tragic case of Nigeria Airways Flight 2120 in 1991 discussed in our previous post, where low tyre pressures and poor decision-making led to a catastrophic accident, let's examine how modern airworthiness regulations aim to decrease the risk of a hazardous or catastrophic tyre failure caused by inadequate tyre inflation pressure.

Part-26 Additional Airworthiness Specifications

When an aircraft is not originally designed to the latest airworthiness specifications, competent authorities may issue Additional Airworthiness Specifications to cope with the new standards. Part-26 addresses the continuing airworthiness and operational safety of aircraft holding a type certificate, mandating inspections, modifications, and other procedures applicable to both the type-certificated design holder (manufacturer) and the operator. While the design holder may provide compliance documentation or approved modification instructions, the operator remains responsible for ensuring conformity with all applicable Part-26 requirements.

EASA CS 25.733(f) and CS 26.201 Requirements

EASA CS 25.733 (f) requires the aircraft to be designed with means to minimise the risk that a tyre is below its minimum serviceable inflation pressure during operation. To comply with this, the type certificate holder, or applicant, can either:

• Include tyre inflation pressure checks in the Instructions for Continued Airworthiness (ICA) at appropriate intervals, or

• Install a monitoring system that either:

  • Alerts the flight crew if tyre pressure falls below the minimum, or

  • Allows pre-flight pressure checks, with the task included in the Aircraft Flight Manual (AFM) procedures.

The counterpart 26.201 also requires operators to minimise the risk of a tyre being below its minimum serviceable inflation pressure during operation. This is a ‘mirrored requirement,’ meaning the operator’s obligations reflect those of the type certificate holder under CS 25.733(f). Compliance can be demonstrated by adherence to CS 25.733(f), or with equivalent requirements:

• Include tyre inflation pressure checks in the Aircraft Maintenance Program (AMP) at appropriate intervals, or

• Install a monitoring system that either:

  • Alerts the flight crew if tyre pressure falls below the minimum, or

  • Allows pre-flight pressure checks, with the task included in the Operations Manual pre-flight procedures.

Note: FAA Parts 25 and 26 are not harmonized with EASA and address this issue primarily through advisory material.

Tyre inflation pressure check in the ICA/AMP

The mirrored requirement ensures that tyre inflation pressure checks are conducted daily, so that the elapsed time between two consecutive checks does not exceed 48 hours. Longer intervals may be allowed if substantiated and approved by the competent authority.

When an aircraft is equipped with a monitoring system, operators may take credit for the system’s measurements to satisfy the required check interval, provided the system reliably reports tyre inflation pressures.

Tyre Pressure Monitoring Systems (TPMS)

If the airplane has a Tyre Pressure Monitoring System (TPMS), it must be designed so that missing an alert or getting a false alert won’t cause serious problems. If the system shows tyre pressure levels, the impact of a false reading is also considered. This includes the possible consequences of one or more tyres failing, even simultaneously, if the airplane is operated with under-inflated tyres.

The mirrored requirement requires that the ICA ensure that the calibration of the tyre pressure monitoring system is maintained / the AMP include tasks, based on the design approval holder’s instructions, to make sure the system stays properly calibrated and works reliably.

Conclusion

The current EASA CS-25 and CS-26 specifications decrease the risk of a hazardous or catastrophic tyre failure in large aeroplane caused by inadequate tyre inflation pressure, requiring design approval holders/applicants and operators to ensure that no tyre falls below its minimum serviceable inflation pressure during operation. This could be achieved either by including a task in the Instructions for Continued Airworthiness (ICA) or Aircraft Maintenance Program (AMP) that requires tyre pressure checks at appropriate intervals (daily or as substantiated), or installing a Tyre Pressure Monitoring System (TPMS) that alerts the flight crew to unsafe tyre pressures.

The regulation is clear. The risk is real. The solution is in how you design your Aircraft Maintenance Program (AMP).