31 July 2011 C1 CIVIL AVIATION DEPARTMENT HONG KONG ...

CIVIL AVIATION DEPARTMENTHONG KONG, CHINAAirworthiness NoticeNo. 5Issue 330 October 2001TYRE WEAR LIMITATIONS1 Introduction1.1 Hong Kong Aviation Requirements require that for certification of new types ofaircraft, the depth of tyre tread below which wet braking friction characteristicsare impaired should be specified at the time of certification; it is also requiredthat it should be possible to determine, in operational conditions, when the treaddepth is worn below this limit.1.2 This Notice provides general guidance on the subject of tyre wear limitationsfor operators of all public transport aeroplanes of more than 5700 kg MaximumTotal Weight Authorised on the Hong Kong Register for which a limiting tyretread depth is not otherwise available.2 Discussion2.1 Accidents and incidents, resulting from both loss of braking friction and loss ofdirectional control on wet runways, continue to occur. While the scheduledaccelerate-stop and landing distances provide some allowance for deteriorationin friction, it has been established that this allowance is not sufficient tomaintain the required level of safety if tyres which are more than 80% worn areused in wet runway operations.2.2 As it is not possible fully to allow for this by increasing the scheduled distances(because of the frequency of incidents caused by loss of directional control,even on the most favourable wheel arrangements), the Director-General favoursthe retention of current scheduled distances, together with a recommendedminimum tread depth applicable to all aircraft tyres.3 RecommendationIn the absence of evidence of the safety of a lower limit for a particularaircraft/tyre/operation combination, it is recommended that a tyre be withdrawn fromservice when it is worn to such an extent that its wet runway performance would beseriously impaired. This may be defined as when:-(a)it is worn such that any groove has a depth of less than 2 mm of tread for moreAN-5 P.130 October 2001