JAR-MMEL/MEL: MASTER MINIMUM EQUIPMENT LIST / MINIMUM EQUIPMENT LIST

Transcription

1 oint Aviation Authorities Postal Address: P.O. Box KA Hoofddorp Visiting Address: Saturnusstraat 8-10 The Netherlands Tel: 31 (0) Fax: 31 (0) Website: 1 August 2005 JAR-MMEL/MEL: MASTER MINIMUM EQUIPMENT LIST / MINIMUM EQUIPMENT LIST Please find attached a copy of Amendment 1 to JAR-MMEL/MEL, effective 1 August A comment/response document, detailing the comments made during consultation and the JAA s replies to those comments, is not appended for this JAR but is available on the JAA website ( Customers who have purchased copies of JAR-MMEL/MEL and wish to receive future amendments, should ensure that they have made suitable arrangements with Information Handling Services, to whom any queries regarding the sale and distribution of JAA documents can be directed. Addresses of the worldwide IHS offices are listed on the JAA website ( and IHS s website ( Queries regarding the technical content of the code should be made to the JAA Headquarters, to the following address: publications@jaa.nl. Luz Mendes NPA & Publications Administrator Chief Executive s office: Administration Division: 31 (0) / (0) Licensing Division: Operations Division: 31 (0) / (0) Airworthiness Division: 31 (0) /780

2 Joint Aviation Requirements JAR-MMEL/MEL Master Minimum Equipment List/ Minimum Equipment List Joint Aviation Authorities

3 Joint Aviation Requirements JAR-MMEL/MEL Master Minimum Equipment List/ Minimum Equipment List Amendment 1 1 August 2005 All rights reserved Printed and distributed by Global Engineering Documents, 15 Inverness Way East, Englewood, Colorado 80112, U S A on behalf of the Joint Aviation Authorities Committee.

4 The members of the Joint Aviation Authorities Committee are representatives of the Civil Aviation Authorities of the countries that have signed the `Arrangements Concerning the Development and the Acceptance of Joint Aviation Requirements`. A list of these countries is kept by European Civil Aviation Conference, 3 bis Villa Emile Bergerat, NEUILLY SUR SEINE Cedex, France. [A list of these countries,* at the issue date of this document can be found at the end of this page.] Further printed copies of the Joint Aviation Authorities Documents can be purchased from Global Engineering Documents, whose world wide offices are listed on the JAA website ( and Global website ( For electronic versions of Joint Aviation Authorities Documents please refer to the website of Information Handling Services (IHS) on where you will find information on how to order. Enquiries regarding the contents should be addressed to the JAA Headquarters, Saturnusstraat 8-10, PO Box 3000, 2130 KA HOOFDDORP, Netherlands ([publications@jaa.nl]). * These countries are: Albania, Armenia, Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, European Aviation Safety Agency, Finland, The Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Monaco, Netherlands, Norway, Poland, Portugal, Republic of Moldova, Romania, Serbia & Montenegro, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey, Ukraine, & United Kingdom. Amendment 1 ii

5 JAR-MMEL/MEL CONTENTS JAR-MMEL/MEL MASTER MINIMUM EQUIPMENT LIST AND MINIMUM EQUIPMENT LIST Paragraph Page Foreword F-1 Check List of Pages CL-1 [Preamble P-1] SECTION 1 - REQUIREMENTS General and Presentation SUBPART A GENERAL JAR-MMEL/MEL.001 Applicability 1-A-1 [JAR-MMEL/MEL.002 Effectivity 1-A-1 JAR-MMEL/MEL.003 Compliance 1-A-1] JAR-MMEL/MEL.005 Terminology 1-A-1 SUBPART B MMEL JAR-MMEL/MEL.010 General 1-B-1 JAR-MMEL/MEL.015 [Types] of Operation 1-B-1 JAR-MMEL/MEL.020 [Preparation of MMEL] 1-B-1 JAR-MMEL/MEL.025 Format and language of MMEL 1-B-1 JAR-MMEL/MEL.030 Multiple Unserviceabilities 1-B-1 JAR-MMEL/MEL.035 Operational and Maintenance Procedures 1-B-1 JAR-MMEL/MEL.040 Rectification Intervals 1-B-2 JAR-MMEL/MEL.045 MMEL [Acceptance] 1-B-2 [JAR-MMEL/MEL.046 MMEL Revisions 1-B-2] SUBPART C MEL JAR-MMEL/MEL.050 General 1-C-1 JAR-MMEL/MEL.055 [Types] of Operation 1-C-1 JAR-MMEL/MEL.060 Preparation of MEL 1-C-1 JAR-MMEL/MEL.065 Format of MEL 1-C-1 JAR-MMEL/MEL.070 Multiple Unserviceabilities 1-C-1 JAR-MMEL/MEL.075 Operational and Maintenance Procedures 1-C-1 JAR-MMEL/MEL.080 Rectification Intervals 1-C-2 [JAR-MMEL/MEL.081 Rectification Interval Extension (RIE) 1-C-2] JAR-MMEL/MEL.085 MEL Approval 1-C-2 JAR-MMEL/MEL.090 Operations outside the scope of the MEL 1-C-2 [ ] SECTION 2 - ADVISORY CIRCULARS JOINT (ACJ) General and Presentation [SUBPART A GENERAL] [ ] ACJ-MMEL/MEL.001([a]) Limit of MEL Applicability 2-A-1 [ACJ-MMEL/MEL.003 Compliance 2-A-1] C-1 Amendment 1

6 JAR-MMEL/MEL [SUBPART B MMEL] [ACJ-MMEL/MEL.010(c) General 2-B-1] ACJ-MMEL/MEL.025 Format of MMEL 2-B-1 ACJ-MMEL/MEL.030 Multiple Unserviceabilities 2-B-1 ACJ-MMEL/MEL.040/.080 Rectification Intervals 2-B-1 Appendix 1 to ACJ-MMEL/MEL.025 Format of MMEL 2-B-3 Appendix 2 to ACJ-MMEL/MEL.025 Specimen MMEL Preamble 2-B-4 [SUBPART C MEL] [ACJ-MMEL/MEL.055 Types of Operation 2-C-1 ACJ-MMEL/MEL.060(b) Preparation of MEL 2-C-1] ACJ-MMEL/MEL.065 Format of MEL 2-C-1 [ACJ-MMEL/MEL.075 Operational and Maintenance Procedures 2-C-1 ACJ-MMEL/MEL.081 Rectification Interval Extension (RIE) 2-C-2] Appendix 1 to ACJ-MMEL/MEL.065 Specimen MEL Preamble 2-C-3 Amendment 1 C

7 JAR-MMEL/MEL FOREWORD 1 The Civil Aviation Authorities of certain European countries have agreed common comprehensive and detailed aviation requirements, referred to as the Joint Aviation Requirements (JAR), with a view to minimising Type Certification problems on joint ventures, to facilitate the export and import of aviation products, to make it easier for maintenance carried out in one European country to be accepted by the Civil Aviation Authority in another European country and to regulate commercial air transport operations. 2 The JARs are recognised by the Civil Aviation Authorities of participating countries as an acceptable basis for showing compliance with their national airworthiness codes. 3 [ ] Whenever the JARs consider aircraft design, or installation and operation of equipment, it is assumed that no known failures exists at the [commencement] of flight. However, with various levels of redundancy designed into aircraft, operation of certain systems or installed equipment may not be required if the remaining operative equipment can maintain an acceptable level of safety. 4 JAR-MMEL/MEL prescribes the conditions for the approval of documents called "Master Minimum Equipment Lists" (MMEL) and "Minimum Equipment Lists" (MEL). 5 The MMEL/MEL is an alleviating document to be used when a failure has been identified. Its purpose is not, however, to encourage the operation of aircraft with inoperative equipment, or to act as a serviceability check list. Such operations are permitted only as a result of careful analysis of each item to ensure that [an acceptable] level of safety is maintained. A fundamental consideration in permitting the dispatch of aircraft with inoperative equipment is that the continued operation of an aircraft in this condition should be limited. 6 Future development of the requirements for this JAR will be in accordance with the agreed amendment procedures. Broadly, these procedures are such that amendment of JAR- MMEL/MEL can be proposed by the Civil Aviation Authority of any of the participating countries and by any organisation represented on the [IPAP (Interested Parties Advisory Panel)]. 7 The meaning of terms and [abbreviations] used in this JAR-MMEL/MEL are contained in this JAR-MMEL/MEL and in JAR-1, Definitions and Abbreviations. 8 Amendments to the text in this JAR-MMEL/MEL are issued as Replacement Pages. These show an effective date and have the same status and applicability as JAR-MMEL/MEL from that date. 9 New, amended and corrected text is enclosed within heavy brackets. 10 Comment/Response Documents developed following Notice of Proposed Amendment (NPA) consultation have been produced by the JAA and are published on the JAA Internet Site: Readers can also apply to JAA Headquarters for copies of specific Comment/ Response Documents as required F-1 Amendment 1

8 JAR-MMEL/MEL INTENTIONALLY LEFT BLANK Amendment 1 F

9 JAR-MMEL/MEL JOINT AVIATION REQUIREMENTS CHECK LIST OF PAGES JAR-MMEL/MEL MASTER MINIMUM EQUIPMENT LIST/MINIMUM EQUIPMENT LIST AMENDMENT 1 DATED The following pages of JAR-MMEL/MEL are now current: Page No Legend Date Title Page Amendment ii Amendment C 1 Amendment C 2 Amendment F-1 Amendment F-2 Amendment CL 1 Amendment CL 2 Amendment P 1 Amendment P 2 Amendment A 1 Amendment A 2 Amendment B 1 Amendment B 2 Amendment C 1 Amendment C 2 Amendment A 1 Amendment A 2 Amendment B 1 Amendment B 2 Amendment B 3 Amendment B 4 Amendment B 5 Amendment B 6 Amendment C 1 Amendment C 2 Amendment C 3 Amendment CL-1 Amendment 1

10 JAR-MMEL/MEL 2 C 4 Amendment C 5 Amendment C 6 Amendment INTENTIONALLY LEFT BLANK Amendment 1 CL

11 JAR-MMEL/MEL [PREAMBLE The initial issue of JAR-MMEL/MEL was published on 1 May Amendment The purpose of this amendment is to incorporate NPA-MMEL/MEL 2 as listed below: Title Page and Verso Revision to title page and status. Revision to verso page to amend addresses and list of the countries. Contents Revision of page numbers where necessary in the contents (details) page. Section 1 Subpart A, B and C Complete re-issue of the whole document arising from NPA-MMEL/MEL 2. Section 2 Subpart A, B and C Complete re-issue of the whole document arising from NPA-MMEL/MEL 2.] P-1 Amendment 1

12 JAR-MMEL/MEL INTENTIONALLY LEFT BLANK Amendment 1 P

13 SECTION 1 JAR-MMEL/MEL SECTION 1 - REQUIREMENTS 1 GENERAL This Section 1 contains the requirements for the approval of Master Minimum Equipment Lists and Minimum Equipment Lists. 2 PRESENTATION 2.1 The Requirements of JAR-MMEL/MEL are presented in two columns on loose pages being identified by the date of the Change number under which it is amended or reissued. 2.2 Explanatory Notes not forming part of the JAR text appear in an smaller typeface. Subheadings are in italic typeface. 1 May

14 JAR-MMEL/MEL SECTION 1 INTENTIONALLY LEFT BLANK May 2000

15 SECTION 1 JAR-MMEL/MEL SUBPART A - GENERAL JAR-MMEL/MEL.005 (continued) JAR-MMEL/MEL.001 Applicability [ ] [(a) Limit of MEL Applicability. The MEL is applicable up to the commencement of flight. (See ACJ-MMEL/MEL.001(a).)] (b) Airworthiness Directives and other Mandatory Requirements. Where there is a conflict between the MMEL [or] MEL and an Airworthiness Directive or any other Mandatory Requirement, it is the data or information contained in the Airworthiness Directive or the Mandatory Requirement (e.g. Continued Airworthiness requirement) which shall override. [ ] [ ] [JAR-MMEL/MEL.002 Effectivity Amendments to JAR-MMEL/MEL become effective 6 months after publication.] [JAR-MMEL/MEL.003 Compliance (See ACJ- MMEL/MEL.003) This JAR will not be applied retrospectively. MMELs and MELs existing prior to 1 May 2000 will continue to remain valid and applicable.] JAR-MMEL/MEL.005 Terminology Terms and [abbreviations] used in JAR- MMEL/MEL have the following meaning: (a) "As required by operating requirements" The listed item of equipment is subject to certain provisions (restrictive or permissive) expressed in the applicable operational requirements. (b) Approved by the Authority means [documented by the Authority as suitable for the purpose intended (Refer to JAR-1).] [(c) "Authority" The competent body responsible for the safety regulation and oversight of Civil Aviation. In the context of JAR- MMEL/MEL Subpart B, this means the Authority of the State of Design. In the context of JAR- MMEL/MEL Subpart C, this means the Authority of the State of the Operator.] [(d)] "Calendar Day" A 24 hour period from midnight to midnight based on either UTC or local time, as selected by the operator. [(e)] "Commencement of flight" The point when an aircraft begins to move under its own power for the purpose of preparing for take off. [(f)] "Day of discovery" The calendar day that a malfunction was recorded in the aircraft maintenance record/log book. [(g) Equipment means item, function, component or system. (h) Flight Day means a 24 hour period (from midnight to midnight) either UTC or local time, as established by the operator, during which at least one flight is initiated for the affected aircraft.] [(i)] "If installed" [means that the] equipment is either optional or is not required to be installed on all aircraft covered by the MMEL. [(j)] "Inoperative" means [ ] that the [equipment] does not accomplish its intended purpose or is not consistently functioning within its design operating limits or tolerances. Some [equipments have] been designed to be fault tolerant and are monitored by [ ] computers which transmit fault messages to a centralised computer for the purpose of maintenance. The presence of this category of message does not [necessarily] mean that the [equipment] is inoperative. [(k) JAA MMEL means the MMEL (including MMEL Supplement) which is recommended by the JAA for acceptance by the Authority.] [(l)] "MEL" An abbreviation for Minimum Equipment List. [(m)] "MMEL" An abbreviation for Master Minimum Equipment List. [(n)] "MMEL Supplement" A list associated with MMELs for aircraft for which application for first type certification is made to a non-jaa Authority. The [Supplement] identifies any A-1 Amendment 1

16 JAR-MMEL/MEL SECTION 1 JAR-MMEL/MEL.005 (continued) differences from the [ ] MMEL [approved by the State of Design]. The [ ] MMEL [approved by the State of Design] and the Supplement constitute the JAA [ ] MEL. [(o) Rectification interval A limitation on the duration of operations with inoperative equipment. (p) RIE An abbreviation for Rectification Interval Extension. (q) Supplemental Type Certificate is defined in JAR 21 / EASA IR Part 21. (r) Supplemental Type Certificate Holder is the holder of, or applicant for, a Supplemental Type Certificate.] [(s)] Type Certificate [ ] [is defined in JAR 21 / EASA IR Part 21.] [(t)] "Type Certificate [H]older" [is the] holder of, or applicant for, a Type Certificate[ ]. INTENTIONALLY LEFT BLANK Amendment 1 1-A

17 SECTION 1 JAR-MMEL/MEL SUBPART B - MMEL JAR-MMEL/MEL.010 General (a) The MMEL is a [ ] [document that lists the equipment which may be temporarily inoperative, subject to certain conditions, while maintaining an acceptable level of safey as intended in the applicable JAR or equivalent Requirement. Each MMEL is specific to an aircraft type.] (b) All items related to the airworthiness of the aircraft and not included in the list are automatically required to be operative. (c) Non-safety related equipment such as galley equipment [and] passenger convenience items, need not be listed [(see ACJ- MMEL/MEL.010(c)]. JAR-MMEL/MEL.015 [Types] of Operation The MMEL shall cover the [types] of operation for which the aircraft type is certificated. JAR-MMEL/MEL.020 [Preparation of MMEL] [ ] [(a) The initial JAA MMEL or JAA MMEL Supplement shall be issued by the Type Certificate Holder. (b) Amendments to the JAA MMEL or JAA MMEL Supplement shall be issued by the Type Certificate Holder or Supplemental Type Certificate Holder, as appropriate. (c) Applications for initial acceptance of an MMEL shall originate from the Type Certificate Holder. (d) Applications for the acceptance of changes to an already accepted MMEL shall originate from either the Type Certificate Holder or a Supplemental Type Certificate Holder, as appropriate.] JAR-MMEL/MEL.025 Format and Language of MMEL (See ACJ- MMEL/MEL.025) (a) The MMEL shall be provided with a relevant Preamble, Definitions and, if appropriate, clarifying Notes which shall adequately reflect the scope, extent and purpose of the List. (b) The MMEL shall be written in a language acceptable to the Authority. JAR-MMEL/MEL.030 Multiple Unserviceabilities (See ACJ- MMEL/MEL.030) The MMEL shall [take into account] the effects of multiple unserviceabilities [ ]. JAR-MMEL/MEL.035 Operational and Maintenance Procedures (a) Operational and Maintenance Procedures are necessary to support certain MMEL items. These Procedures shall be [ ] [produced and published by the Type Certificate Holder or the Supplemental Type Certificate Holder, as appropriate. The procedures shall be appropriately amended, as and when the MMEL is revised. (b) The intent of these procedures shall be identified during the development of the MMEL. However, the procedures themselves will not be subject to approval.] [(c)] These procedures shall be referenced in the MMEL and published concurrently with the MMEL [ ]. [ ] B-1 Amendment 1

18 JAR-MMEL/MEL SECTION 1 JAR-MMEL/MEL.040 Rectification Intervals (See ACJ- MMEL/MEL.040/.080) The MMEL shall provide [categories] A, B, C and D, Rectification Intervals. The category of each inoperative item shall be determined according to the requirements specified below: (a) Category A: (i) No standard interval is specified, however, items in this category shall be rectified in accordance with the conditions stated in the MMEL. (ii) Where a time period is specified [in calendar days] it shall start at 00:01 on the calendar day following the day of discovery. (b) Category B: Items in this category shall be rectified within three consecutive calendar days, excluding the day of discovery. (c) Category C: Items in this category shall be rectified within ten consecutive calendar days, excluding the day of discovery. (d) Category D: Items in this category shall be rectified within one hundred and twenty consecutive calendar days, excluding the day of discovery. INTENTIONALLY LEFT BLANK JAR-MMEL/MEL.045 MMEL [ Acceptance] [ ] [(a) New JAA MMELs and amendments to existing JAA MMELs will only be accepted in accordance with this JAR-MMEL/MEL Subpart B. (b) The JAA MMEL (including MMEL Supplement) shall be recommended to the Authorities for their acceptance. It is the responsibility of each Authority to accept the MMEL for use by their operators.] [JAR-MMEL/MEL.046 MMEL Revisions The Type Certificate or Supplemental Type Certificate Holder, as appropriate, shall positively inform all known operators when a revision to the JAA MMEL (including MMEL Supplement) is published.] Amendment 1 1-B

19 SECTION 1 JAR-MMEL/MEL SUBPART C - MEL JAR-MMEL/MEL.060(c) (continued) JAR-MMEL/MEL.050 General (a) The MEL is [ ] [a document that lists the equipment which may be temporarily inoperative, subject to certain conditions, at the commencement of flight.] This [document] is prepared by the operator for his[/their] own particular aircraft taking account of their aircraft [configuration] and the relevant operational and maintenance conditions in accordance with a procedure approved by the Authority. (b) All items related to the airworthiness of the aircraft and not included in the list are automatically required to be operative. (c) Non-safety related [equipment,] such as galley equipment [and] passenger convenience items, need not be listed. Operators shall establish an effective decision making process for failures that are not listed to determine if they are related to airworthiness and required for safe operation [(see ACJ-MMEL/MEL.010(c))]. (d) The MEL may contain additional advisory material or modified operational and maintenance procedures. revision to [submit the revised MEL to the Authority.] [(d)] Reduced time scales for implementation of safety related revisions may be required. JAR-MMEL/MEL.065 Format of MEL (See ACJ- MMEL/MEL.065) (a) The MEL shall contain a relevant Preamble, Definitions and, if appropriate, clarifying Notes which shall adequately reflect the scope, extent and purpose of the List. (b) The MEL shall indicate the revision status of the MMEL, upon which it is based. (c) The Preamble shall contain [ ] guidance [for] flight crews [and maintenance personnel] using the MEL. JAR-MMEL/MEL.070 Multiple Unserviceabilities JAR-MMEL/MEL.055 [Types] of Operation [(See ACJ- MMEL/MEL.055)] With the agreement of the Authority, the MEL may include specific provisions for particular [types] of operation carried out by the operator (e.g. [c]rew [t]raining, [p]ositioning [f]lights, [d]emonstration [f]lights etc.) JAR-MMEL/MEL.060 Preparation of MEL (a) The MEL,[including the Preamble and Definitions,] shall be based upon, but no less restrictive than, the relevant MMEL (if this exists) [accepted] by the Authority. [(b) If no such MMEL exists, the MEL may be based upon an alternative MMEL in agreement with the Authority (see ACJ-MMEL/MEL.060(b)).] [(c)] When a [ ] MMEL revision [ ] is issued, an operator will have 90 days from the date of [ ] The operator shall ensure that the MEL, including the Preamble, reflects the guidance given in the MMEL on the effects of multiple unserviceabilities. JAR-MMEL/MEL.075 Operational and Maintenance Procedures [(See ACJ- MMEL/MEL.075)] (a) Operators shall take Operational and Maintenance procedures referenced in the MMEL into account when preparing an MEL. [An operator shall be prepared to present these procedures to the Authority during the MEL approval process.] (b) Operational Procedures shall be accomplished in planning for and/or operating with the listed item inoperative. Normally these procedures are accomplished by the flight crew; however, other personnel may be qualified and authorised to perform certain functions. The satisfactory accomplishment of all procedures, regardless of who performs them, is the responsibility of the operator. Appropriate C-1 Amendment 1

20 JAR-MMEL/MEL SECTION 1 JAR-MMEL/MEL.075(b) (continued) procedures are required to be published as a part of the operator s manual or MEL. (c) Maintenance Procedures shall be accomplished prior to operating with the listed item inoperative. Normally these procedures are accomplished by maintenance personnel; however, other personnel may be qualified and authorised to perform certain functions. The satisfactory accomplishment of all maintenance procedures, regardless of who performs them, is the responsibility of the operator. Appropriate procedures are required to be published as a part of the Operator s Manual or MEL. (d) The procedures themselves, or symbols [indicating their need and reference to their location], are required in the operator s MEL. (e) The MEL shall be appropriately amended, as and when applicable operations or maintenance procedures as referenced in the MMEL [JAR-MMEL/MEL.081 Rectification Interval Extension (RIE) (See ACJ- MMEL/MEL.081) Subject to the approval of the Authority, the operator may use a procedure for the extension of the applicable Rectification Intervals B, C and D, for the same duration as specified in the MEL, provided: (a) A description of specific duties and responsibilities for controlling extensions is established by the operator and accepted by the Authority, and (b) The operator only grants a one time extension of the applicable Rectification Interval, and are revised. (c) The Authority is notified of any [ ] extension granted within a timescale acceptable to the Authority, not to exceed one month, and [(f) ] Unless specifically permitted, an inoperative item may not be removed from the aircraft. (d) Rectification is accomplished at the earliest opportunity.] JAR-MMEL/MEL.080 Rectification Intervals (See ACJ- MMEL/MEL.040/ 080) (a) The operator shall take account of the Rectification Interval given in the MMEL when preparing an MEL. [The Rectification Interval in the MEL shall not be less restrictive than the corresponding Rectification Interval in the MMEL.] [ ] [(b)] The operator is responsible for establishing an effective rectification programme that includes tracking of the inoperative items and co-ordinating parts, personnel, facilities, and procedures necessary to ensure timely rectification. [(c)] [Operation] of the aircraft is not allowed after expiry of the Rectification Interval specified in the MEL, unless: JAR-MMEL/MEL.085 MEL Approval [ ] [New MELs and amendments to existing MELs will only be approved in accordance with this JAR-MMEL/MEL Subpart C.] [(i)] The defect has been rectified, [or] [(ii)] The Rectification Interval is extended in accordance with [ ] [JAR-MMEL/MEL.081] [ ] JAR-MMEL/MEL.090 Operations Outside the Scope of the MEL [ ] [ ] [Notwithstanding JAR-MMEL/MEL.081, subject to the approval of the Authority, the operator may be exempted from compliance with the appropriated MEL provided such exemption complies with applicable limitations in the MMEL.] Amendment 1 1-C