Chapter 10.2.1
Classification of Modifications
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2.2 Contractor and pre-release application
2.4 Classification of modifications issued to AECMA specification 1000D
2.5 Riders and notes to classifications
3 Effect of modification classification on spares
When a modification is authorized by the appropriate Modifications Committee (MC), it will be given a classification in accordance with the agreed coding system to indicate the urgency of embodiment and who is authorized to embody it. The classifications may also carry a qualifying statement or rider giving additional information.
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This chapter is applicable to all Designer modifications. It is not applicable to Service 43Modifications (SM) or some guided weapon and multinational aircraft and projects.
Modifications to be carried out by a contractor are classified by letter and those to be embodied by the Services are classified by number. Modifications may be classified with both.
The coding system can be conveniently divided into:
1 Pre-release application (classified AA).
2 Contractor application (classified A, B, C or D).
3 Service application (classified 1, 2, 3, 4 or 0).
4 Special Order Only (SOO/E) (classified SOO or E).
2.2 Contractor and pre-release application
The following letter classifications apply to aircraft, engines and equipment in production and to engines and equipment being overhauled by the Contractor Repair Organization (CRO), DARA and designated Service Repair Facilities.
1 Class AA – Modifications essential for initial MA Release of a new type or mark of aircraft or for the introduction of new equipment and must be embodied prior to delivery to the Service.
2 Class A – Modifications essential for safety and must be embodied irrespective of the delay involved. The absence of a Class A modification may involve the grounding of the aircraft, a flight limitation or a limitation of its operational role.
3 Class B – High priority modifications, the non-embodiment of which imposes operational limitations or reduces maintenance efficiency. Parts will be made available as soon as practicable and embodied forthwith during reconditioning or repair. The MC may also authorize delay in the delivery of any aircraft or equipment being produced in order to ensure embodiment and/or the scrapping of pre-mod parts.
4 Class C – Modifications that are important improvements for technical and operational reasons and are embodied in production, provided there is no delay in delivery. These modifications should also be embodied retrospectively during reconditioning or repair. In the case of repair only, the embodiment is limited to those modifications that do not require additional stripping beyond that necessary to complete the repair. Scrapping of existing parts is permissible when authorized by the appropriate MC.
5 Class D – Modifications of a lesser importance that are embodied in new production, provided no scrap or delay is involved. In service, Class D modifications are embodied when stocks of unmodified spares are exhausted.
6 SOO/Class E – The term SOO is applied to modifications that are necessary to achieve a limited specified objective. In the case of Anglo-French modifications, the classification E is used in lieu of SOO. The MC will define the limited requirements and the particular aircraft, engine or equipment in which the modification is to be embodied.
The following classifications apply to aircraft, engines and equipment in service and aircraft on scheduled maintenance or modernization in DARA and Service Repair Facilities. The classifications also apply to serviceable equipment in equipment store depots.
1 Class 1 – Modifications essential for safety, the absence of which imposes a severe limitation on the use of aircraft or equipment. The aircraft may be grounded until the necessary modification is embodied.
2 Class 2 – High priority modifications, the absence of which imposes operating limitations or seriously reduces maintenance efficiency.
3 Class 3 – Modifications of a lower category than Class 2, but the gain in operational efficiency or reliability, or economy of operation, servicing or maintenance, is judged to outweigh the cost and effort of retrospective embodiment.
4 Class 4 – Modifications that are normally embodied on replacement of defective parts when all spares to the original specifications have been used. They do not affect the interchangeability of spares.
5 Class 0 – Modifications that will not be embodied in service, but where interchangeability of Service spares may be affected.
6 SOO/Class 5 – The term SOO is applied to modifications that are necessary to achieve a limited specified objective. They will be embodied to a limited number of aircraft or equipments. In the case of Anglo-French modifications, the classification 5 is used in lieu of SOO. The MC will define the limited requirements and the particular aircraft, engine or equipment in which the modification is to be embodied.
2.4 Classification of modifications issued to AECMA specification 1000D
Some modifications are issued to the Service as Service Bulletins to the AECMA 1000D specification. These are categorized as follows:
1 Category 1 – Do before next flight or before XX hrs, YY cycles, or a specific date or interval. Compliance is mandatory, generally in support of an airworthiness authority’s action.
2 Category 2 – Not applicable.
3 Category 3 – Not applicable.
4 Category 4 – Do when (area) is next exposed.
5 Category 5 – Do as soon as the affected part is removed from the higher assembly (air vehicle, engine, etc).
6 Category 6 – Do when the part is next repaired.
7 Category 7 – Do at customer convenience/option.
8 Category 8 – Spare part information only.
9 Category 9 – Information only.
2.5 Riders and notes to classifications
2.5.1 Riders
The timing or method of embodiment of a modification may be specified by an appropriate rider to the Service application as follows:
1 Working Party – The modification is to be embodied by a Contractor’s Working Party (CWP) or Service Modification Party or (SMP).
2 On Removal of Unmodified Item – The modification should be embodied on the first occasion that the item itself is removed or some other part is removed which gives access. For example, on removal of engine or tailplane.
3 On Replacement of Unmodified Item – The modification should be embodied on the first occasion that the item becomes unserviceable and is replaced, subject to a modified item being available.
4 By Return of Unmodified Item – On return to contractor or Service Repair Centre. This means that embodiment is beyond the scope of 4Forward maintenance organizations.3 In order to maintain a flow of unmodified items to the contractor or repair unit, it is necessary to fit the modified item and return the unmodified item as directed as soon as possible. A specific return programme may be set up by the IPT.
5 WOTSAC (When Old Type Spares are Consumed) – This indicates that interchangeability is affected and work has to be done to the aircraft or equipment to enable post-mod spares to be fitted. As a result, old type spares will no longer fit and the modification will be embodied ‘when the old type spares are consumed’.
6 NOROR – The modification will ‘not be embodied on repair or reconditioning’.
7 NIP – The modification will ‘not be embodied in new production aircraft/ engines/ equipments’.
8 Satisfied by – ‘Satisfied by’, followed by an SM or STI number, means that the work of the nominated instruction does not differ significantly from that of the subsequent Designer modification. No further work is required on aircraft or other equipment on which the earlier instruction has been satisfied.
9 Superseding – ‘Superseding’ followed by an SM or STI number, means that there are significant differences between the nominated instruction and the superseding Designer modification. Further work is required to satisfy the Designer modification and both pre- and post-SM/STI modification leaflets will be provided.
10 ‘On Failure’, ‘On Fault’ or ‘On Need to Repair’ – These riders are self-explanatory.
2.5.2 Notes
Modification classifications may also be amplified by notes, the most common examples of which are:
1 NCP (No Contractor’s Parts) – If parts are necessary to embody the modification they are not to be obtained from the contractor, but from Service sources. This note also applies when no parts are needed for rework.
2 RPO (Record Purposes Only) – This term is used for the initiation of drawing changes to the Master Record Index (MRI), Drawing Introduction Sheet (DIS) or for recording information. No action is required by the Service as a result of the modification.
3 ROP (Reverse Order of Priority) – Modification sets will be issued for Service embodiment before issue to the contractor.
3 Effect of modification classification on spares
Modifications may affect spares either already made or yet to be produced. Spares affected by Class AA or Class 1 modifications are to be modified or replaced by modified items before use. When it is necessary to retain both modified and unmodified equipment in service, the IPT is responsible for provisioning and supplying any necessary spares.