Chapter 5.4.2
Deferment of Maintenance – Guidance on the Use of Limitations and Acceptable Deferred Faults
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4.1 Categories of maintenance that are potentially suitable for deferment
7 Follow-up action by the 4PT3 or FLC
8 Analysis of deferred fault trends
9 ADF Log forms with special applicability
10 Authorization to defer maintenance
Aircraft, and role equipment subject to MOD Form 700 management, are to be maintained in accordance with the regulations and limits detailed within the aircraft document set (ADS) or Technical Information (TI). However, where operational needs dictate or where it is expedient to do otherwise, it may be necessary to authorize deferment of maintenance that is outside the ADS or TI limits. This chapter provides guidance on factors to be considered and actions to be taken on these occasions.
For guidance on deferment of scheduled maintenance, which is recorded in MOD Form 700 Section 5, see Chapter 5.3.
This chapter is associated with the following publications:
1 JAP 100A-01 Chapter 5.4 – Corrective Maintenance.
2 JAP 100A-01 Chapter 7.2 – Recording of Aircraft Maintenance.
3 MOD F799/2 – Instructions for Use for MOD F703 series forms.
4 MOD F799/3 – Instructions for Use for MOD F704 series forms.
5 JAP 100N-0409-1 – Work Recording and Asset Management System On-Line Procedures Manual.
The information in this chapter is applicable both to hard copy documentation (eg MOD F700C) and electronic documentation hosted on Logistics Information Systems (LIS).
2 Policy on deferment of maintenance – guidance on use of the Limitations Log (Lim Log) and the Acceptable Deferred Faults Log (ADF Log)
There are occasions when it is not possible to complete a maintenance task before an aircraft is required for flight. Alternatively it is sometimes more efficient to carry out a maintenance task at the same time as other work, such as scheduled maintenance, is undertaken. In such cases, maintenance may be deferred by suitably authorized personnel if considered justifiable and safe.
A person holding authorization JAP G-346 may defer maintenance either:
1 By permitting, in consultation and agreement with the appropriate operations staff, further flight/s with a specified limitation on operation or handling, as recorded in the Limitations Log (Lim Log) (MOD F703).
2 By declaring the fault/damage acceptable for further flight without limitation and raising an entry in the Acceptable Deferred Fault Log (ADF Log) (MOD F704).
Deferring maintenance carries risk. When considering deferment, the authority level G must assess the associated risks and consider all factors that will mitigate the risk. The mitigating factors are to be adequately documented in the appropriate maintenance work order/aircraft job report.
4.1 Categories of maintenance that are potentially suitable for deferment
Deferrable maintenance can be regarded as falling into the following categories:
1 Faults and damage defined as acceptable within limits stated in the ADS/TI.
2 Out-of-limit faults and damage.
3 Faults and damage for which no limits are given.
4 Maintenance activities that necessarily deviate from relevant TI.
4.1.1 Faults and damage defined as acceptable within limits stated in the ADS/TI
Acceptable faults and damage are those that are within 4Design Organization (DO)3 or 4Project Team (PT)3 defined safe limits as published in the ADS/TI and for which deferred rectificationis authorized, or no rectification is necessary. Because of their known status, such faults and damage carry the lowest level of risk; however, their deferment is to be recorded in order to ensure that:
1 The fault or damageis rectified at a suitable maintenance opportunity.
2 The fault or damageis monitored to check for further degradation.
3 Repetitive reporting of the fault or damageis eliminated.
Recording of deferred acceptable faults and damageis normally made in the ADF Log, unless the fault or damage is the subject of a purpose-designed ADF Log (eg MOD Form 704C); see paragraph 9.
4.1.2 Out-of-limit faults and damage
Out-of-limits faults and damage are those that are beyond 4DO3 or4PT3defined limits published in the ADS or TI and would usually require immediate rectification. In such cases deferment may carry an increased level of risk. Thus, greater risk mitigation measures, such as limiting the relevant aspects of the flight envelope will need to be considered, (see paragraph 4.2 for other factors to consider) and it must be clearly determined that the43 requirement outweighs any additional airworthiness risks before any deferment is authorized. As soon as is practicable, cases are to be referred to the4PT3for advice on the airworthiness risk, stressing the urgency. Whilst awaiting further guidance, deferment may be granted and is to be recorded in the Lim or ADF Log as appropriate.
4.1.3 Faults and damage where no limits are given
In cases where a fault or damage is not recognized in the ADS/TI, the level of risk is uncertain, as historical data and experience of such faults and damage is unlikely to be available. Consequently, the risk assessment is likely to require more of the mitigating factors listed at paragraph 4.2 to be taken into account, 4and it must be clearly determined that the requirement outweighs any additional airworthiness risks before any deferment is authorized. If, after the risk assessment, the person authorizing the deferment deems that further advice is required the case is to be referred to the PT as soon as is practicable for advice on the airworthiness risk, stressing the urgency. Deferment may be granted and is to be recorded in the Lim or ADF Log as appropriate.3
4.1.4 Maintenance activities that necessarily deviate from relevant TI
There may be occasions when a maintenance activity cannot comply with a relevant TI, eg through resource deficiencies or the TI itself proves to be unworkable.4In normal circumstances, the maintenance is to remain incomplete until resources are available, or amendments to TI are approved and promulgated (see Chapter 8.2 for TI amendment procedures, both routine and urgent). However, a requirement may necessitate a maintenance activity being completed prior to resources becoming available or a TI amendment being approved by the PT.
Notes:
1 Resource deficiencies are defined as a lack of GSE, STTE, tools, or Suitably Qualified and Experienced Personnel (SQEP).
2 Unworkable TI is defined as TI that cannot be complied with because the descriptive or procedural information is incomplete, inconsistent or illogical.
3 This category is not to be used for deferring faults and damage that is either in or out of ADS/TI limits or for where no limits are given, as detailed in paragraph 4.1.
The action required to resolve the issue is as follows:3
4.1.4.1 Deviation from TI within a Forward organization
When a maintenance activity cannot be completed in time to meet 4a 3requirement due to a lack of resources or the inability to follow the relevant TI (eg awaiting4PT3direction) a risk assessment is to be carried out considering the factors listed in paragraph 4.2 to establish the degree of risk. If the risk is considered acceptable, the lack of resource or the inability to follow TI is to be documented and 4deviation3 authorized as follows:
1 The related MWO is to include the following information:
1.1 Details of the reasons for the deviation, ie resource shortage or unworkable TI.
1.2 Details of the alternative maintenance activity carried out to allow the deviation to be safely deferred.
1.3 In the case of unworkable TI, details of action taken in accordance with JAP 100A-01 Chapter 8.2 and Chapter 8.2.1 to notify the error to the TI sponsor (and platform4PT3if not the TI sponsor).
1.4 Endorsement by a person holding authorization JAP G-346 4stating3 that the circumstances justify proceeding with the deviation and that deviation is authorized.
1.5 A Lim or ADF Log entry authorized by a person holding authorization JAP G-346.
2 The related Lim or ADF Log entry is to:
2.1 Provide details of the deviation and the required recovery action.
2.2 State the operational justification for proceeding with the deviation.
2.3 Be authorized by a person holding authorization JAP G-346.
2.4 Be deferred for review for a period not exceeding 7 calendar days: hastening action is to be taken if there has been no response from the4PT3for TI-related issues or the FLC for other resource issues, within this timescale.
2.5 In the case of unworkable TI, include the reference of the Urgent Amendment Proposal raised in accordance with JAP 100A-01 Chapter 8.2.1.
3 The deviation is to be notified to the platform4PT3and the FLC at the earliest practicable opportunity; see also paragraph 7.
4.1.4.2 Deviation from TI within a Depth organization
Depth organizations are not to deviate from TI. If it is found that a maintenance activity within a Depth organization cannot comply with relevant TI or the TI is found to be unworkable, the maintenance activity is to remain incomplete until resources are available, or amendments to TI are approved and promulgated (see Chapter 8.2 for TI amendment procedures, both routine and urgent) or as directed by the relevant 4PT3.
Before making a decision whether or not to defer maintenance, a person holding authorization JAP G-346 is to assess the consequences and/or hazards and associated risk of deferment. The following factors, which are neither prescriptive nor exhaustive, should be considered:
1 Presence of concessions or prescribed fault/damage limits authorized within the ADS/TI.
2 Personal knowledge and experience, knowledge and experience of local experts and relevant information.
3 Consequences or likelihood of failure.
4 Consequences or likelihood of further deterioration.
5 Precedence, based on same or similar occurrences.
6 Imposition of limitations in order to reduce further deterioration/possibility of failure.
7 Aircrew experience/workload/tasking.
8 Flight profile/duration/prevailing conditions.
9 Period of deferment.
10 Ongoing examinations of the fault/damage and any limits of tolerable further degradation.
11 Frequency of examinations.
12 Temporary repairs.
13 Remedial actions to prevent further damage.
14 Action to assist future examinations (eg removing paint around cracks or marking crack length).
15 Photographs or sketches of the fault/damage for comparison on future examination and transmission to specialists.
16 Documenting, if appropriate, for future trend analysis.
17 Contacting the 4PT3/Front Line Command for further advice or knowledge of previous occurrences, particularly for new/unusual damage.
18 Challenging the 4PT3 if it is believed that prescribed limits are too restrictive.
19 Narrative fault reporting in accordance with Chapter 7.5.1 or serious fault signal procedure in accordance with Chapter 7.5.2.
20 Assessment and categorization in accordance with Chapter 9.13.1.
21 Requesting new repair instructions in accordance with Chapter 9.13.2.
If rectification of a fault that will affect the aircraft’s role or handling is to be deferred, the deferment details are to be entered in the Lim Log in accordance with the appropriate - Instruction For Use (IFU) (eg MOD F799/2). Where appropriate, limitations should be formulated in consultation with aircraft operators.
If rectification of a fault that will not affect the aircraft’s role or handling is to be deferred, the deferment details are to be entered in the ADF Log in accordance with the appropriate IFU (eg MOD F799/3).
Any deferment is to be for a specified period (eg calendar time, one flight only, restricted number of flights, flying hours, etc), or to a nominated flight servicing, scheduled maintenance or review date, when the maintenance is to be undertaken or the deferment reviewed. When deferring to a specific scheduled maintenance activity and if the nature of the deferment warrants it, consideration should be given to stating a usage and/or calendar backstop to ensure that the entry is reviewed should the maintenance be extended.
Extensions to the period of deferment are to be carried out in accordance with the relevant IFU.
7 Follow-up action by the 4PT3 or FLC
A 4PT3 or FLC that has been notified of a deviation from TI is to consider the implications and is to:
1 Acknowledge receipt within 48 hrs.
2 Provide a formal response and statement of intent within the originator’s deferment period.
3 Take appropriate remedial action to resolve the issue.
8 Analysis of deferred fault trends
4PTs3 are responsible for ensuring the continuing airworthiness of their aircraft and a system of assessment is to be in operation to provide a continual analysis of all deferred faults; Chapter 5.1 refers.
9 ADF Log forms with special applicability
There are a number of additional forms in the ADF Log (MOD Form 704) series that have special applicability as follows:
1 MOD F704A – Acceptable Deferred Husbandry Log.
2 MOD F704B – Engineering Changes Affecting Maintainability.
3 MOD Form 704C – Platform-Specific Records/Registers.
4 MOD F704D – 4PT3-Granted Concessions (see Chapter 5.1).
5 MOD F704E – List of Modifications and Service Issued Instructions with Maintenance or Configuration Implications.
Instructions for the use of the above forms are contained in the relevant MOD Form 799.
10 Authorization to defer maintenance
Personnel required to defer maintenance are to hold authorization JAP G-346.