CS 25.733 Tyres — CS-25

IRImplementing rule

CS 25.733Tyres

(a)When a landing gear axle is fitted with a single wheel and tyre assembly, the wheel must be fitted with a suitable tyre of proper fit with a speed rating approved by the Agency that is not exceeded under critical conditions, and with a load rating approved by the Agency that is not exceeded under –

(1)The loads on the main wheel tyre, corresponding to the most critical combination of aeroplane weight (up to the maximum weight) and centre of gravity position; and

(2)The loads corresponding to the ground reactions in sub-paragraph (b) of this paragraph, on the nose-wheel tyre, except as provided in sub-paragraphs (b)(2) and (b)(3) of this paragraph.

(b)The applicable ground reactions for nosewheel tyres are as follows:

(1)The static ground reaction for the tyre corresponding to the most critical combination of aeroplane weight (up to maximum ramp weight) and centre of gravity position with a force of 1·0 g acting downward at the centre of gravity. This load may not exceed the load rating of the tyre.

(2)The ground reaction of the tyre corresponding to the most critical combination of aeroplane weight (up to maximum landing weight) and centre of gravity position combined with forces of 1·0 g downward and 0·31 g forward acting at the centre of gravity. The reactions in this case must be distributed to the nose and main wheels by the principles of static’s with a drag reaction equal to 0·31 times the vertical load at each wheel with brakes capable of producing this ground reaction. This nose tyre load may not exceed 1·5 times the load rating of the tyre.

(3)The ground reaction of the tyre corresponding to the most critical combination of aeroplane weight (up to maximum ramp weight) and centre of gravity position combined with forces of 1·0 g downward and 0·20 g forward acting at the centre of gravity. The reactions in this case must be distributed to the nose and main wheels by the principles of static’s with a drag reaction equal to 0·20 times the vertical load at each wheel with brakes capable of producing this ground reaction. This nose tyre load may not exceed 1·5 times the load rating of the tyre.

(c)When a landing gear axle is fitted with more than one wheel and tyre assembly, such as dual or dual-tandem, each wheel must be fitted with a suitable tyre of proper fit with a speed rating approved by the Agency that is not exceeded under critical conditions, and with a load rating approved by the Agency that is not exceeded by –

(1)The loads on each main wheel tyre, corresponding to the most critical combination of aeroplane weight (up to maximum weight) and centre of gravity position, when multiplied by a factor of 1·07; and

(2)Loads specified in sub-paragraphs (a)(2), (b)(1), (b)(2) and (b)(3) of this paragraph on each nose-wheel tyre.

(d)Each tyre installed on a retractable landing gear system must, at the maximum size of the tyre type expected in service, have a clearance to surrounding structure and systems that is adequate to prevent unintended contact between the tyre and any part of the structure or systems.

(e)For an aeroplane with a maximum certificated take-off weight of more than 34019 kg (75 000 pounds), tyres mounted on braked wheels must be inflated with dry nitrogen or other gases shown to be inert so that the gas mixture in the tyre does not contain oxygen in excess of 5% by volume, unless it can be shown that the tyre liner material will not produce a volatile gas when heated, or that means are provided to prevent tyre temperatures from reaching unsafe levels.

(f)A means shall be provided to minimise the risk that a tyre is below its minimum serviceable inflation pressure during operation. (See AMC 25.733(f))

[Amdt 25/26]

IR · CS 25.733 — CS-25 · ED Decision 2020/024/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

AMCAcceptable means of compliance

AMC 25.733(f)Tyre inflation pressure check

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1.General ‘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. In order to demonstrate compliance with CS 25.733(f), the applicant should use one, or a combination, of the following means:

(a)Provide a task in the Instructions for Continued Airworthiness (ICA) that requires tyres inflation pressure checks to be performed at a suitable time interval,

(b)Install a system that monitors the tyres inflation pressures and:

(1)provides an alert to the flight crew, in compliance with CS 25.1322, whenever a tyre inflation pressure is below the minimum serviceable inflation pressure, or

(2)allows the tyres inflation pressures to be checked prior to the dispatch of the aeroplane, and a tyre inflation pressure check task is included in the Aeroplane Flight Manual (AFM) pre-flight procedures.

2.ICA Tyre inflation pressure check A ‘suitable time interval’ is the maximum time interval between two consecutive tyre inflation pressure checks. Checks should be conducted daily in order to ensure that the elapsed clock time between two consecutive tyre inflation pressure checks does not exceed 48 hours. Time intervals longer than 48 hours may be used if they are substantiated and agreed by EASA. This substantiation should at least include an analysis of the expected loss of tyre pressure during operation, taking into account the environmental and operational factors, including the potential for pressure loss at a rate that exceeds the normal diffusion resulting from damage to or degradation of the tyre/wheel assembly. If available, statistical data related to pressure losses gathered from the service experience of aeroplanes equipped with equivalent wheel designs should also be used. The substantiation should be made in cooperation with the tyre manufacturer(s). In addition, the applicant may take credit from an installed system monitoring the tyre inflation pressures.

3.Tyre inflation pressure monitoring systems If a system is installed, its development assurance level should be commensurate with the potential consequences of an alert not being provided, as well as with the consequences of false alerts. If the system includes the indication of tyre pressure levels, the consequence of a false indication should also be taken into account. The assessment of these consequences should include the effects of the failure of one or more tyres (including simultaneous tyre failures) that may be caused by the operation of the aeroplane with under-inflated tyres. Instructions for Continued Airworthiness should be provided to ensure that the calibration of the tyre pressure monitoring system is maintained.

[Amdt 25/26]

AMC · AMC 25.733(f) — CS-25 · ED Decision 2020/024/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023