CS MMEL.145 Justification
of MMEL items
ED Decision 2020/012/R
(a) The justifications are provided by the applicant along with each MMEL item.
(b) The inclusion of each item in the MMEL is justified following one or more methods, also referred to as MMEL safety methodologies, as agreed with EASA.
(c) The justifications include at least a qualitative safety assessments which:
(1) evaluate the consequences of the proposed MMEL dispatch configuration on the aircraft functional capabilities, crew workload and discomfort to occupants and show compliance with CS MMEL.140;
(2) evaluate the consequences of the next worst safety-related failure and, if applicable for the item, separately evaluate the consequences of the external event for which the item was designed to protect against, and ensure the combination of the MMEL dispatch configuration with the next worst safety-related failure or event do not correspond to an hazardous or catastrophic failure condition; and
(3) notwithstanding paragraph (2) above, specific cases may be accepted when supported by quantitative safety assessment as per paragraph (d) below.
(d) The qualitative safety assessment is supplemented by a quantitative safety assessment when both of the following considerations are met:
(1) relief is proposed for items, functions and/or systems involved in catastrophic or hazardous failure conditions, and the severity of the failure condition under MMEL configuration is not mitigated by special operating conditions, limitations or procedures; and
(2) when the operation with the inoperative item leaves the aircraft one failure away from a hazardous failure condition, or one or two failures away from a catastrophic failure condition.
(e) When an operational or maintenance procedure is associated to an MMEL item, corresponding symbol is included in the MMEL, and the intent of the procedure is specified in the associated item justification.
(f) Where a detailed quantitative analysis is required, notwithstanding paragraph (d), a qualitative analysis may only be used for conventional and simple systems when the aircraft is certified against requirements other than CS 25/29.1309.
Issue No: MMEL/2
EASA MMEL regulations require thorough justification for each item, including qualitative safety assessments evaluating dispatch configuration consequences. Quantitative assessments are needed for items linked to hazardous or catastrophic failures, especially without mitigating procedures. Operational or maintenance procedures linked to items must be clearly specified.
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