Appendix C to AMC 20-21 Determination if a major change to an
aircraft should be specifically subjected to an EZAP
ED Decision 2008/007/R
The EZAP provides a means for TC and STC holders to develop improvements to EWIS maintenance programs. These improvements will be in the form of new inspections and other tasks designed to prevent significant accumulation of combustible materials on or adjacent to EWIS components that would be added to the Instructions for Continued Airworthiness or Service Bulletins (SB) for the aircraft and STC.
While TC holders are required to conduct the EZAP for all zones in an aircraft, it may be determined that EZAP for an SB or STC is not necessary where the modification does not appreciably affect the zones where it is installed. The “Determination if SB modification or STC requires EZAP” procedure was developed to identify modifications that sufficiently affect zone attributes to warrant re-application of EZAP to the entire zone.
This logic assumes that the aircraft TC holder has accomplished the EZAP on each zone of the aircraft without consideration of the SB modification or STC installation. The objective of this analysis is to assess whether the modification itself has affected wiring or certain zone attributes that could change the outcome of the EZAP performed by the aircraft TC holder.
The determination if the SB or STC requires EZAP, and
re-application of the EZAP to SB or STC affected zones, is the responsibility
of the respective holder of the SB or STC. It is expected that the TC and STC
holders will collaborate with each other and operators as necessary to obtain
In situations where a previously installed STC is no longer supported by a viable STC holder (e.g. STC holder defunct), the responsibility for determining if the STC requires EZAP, and re-application of EZAP to any affected zones, is assigned to the individual operators who utilise the STC on their aircraft. In cases where the operator does not have experience in application of analytical logic processes, it will be necessary for the operator to gain competence in, or seek external assistance in conducting the analysis.
A record of the outcome of operator accomplished analysis for STC (even if no tasks are identified) should be permanently retained by the operator. A copy of the record should be included in the aircraft records normally transferred upon change of aircraft operator.
The attached logic chart provides a means to assess whether an SB modification or STC has sufficiently affected wiring or certain other zone attributes as to require reapplication of the EZAP to the entire zone with consideration of the modification present. The section following the chart provides detailed explanations of each step in the “Determination if SB modification or STC requires EZAP” with appropriate examples.
It is recommended that, where possible, the analyst should utilise the availability of actual aircraft to ensure they fully understand the zones being analysed. Specifically, it must be determined how installation of the modification could affect zone attributes such as density, environment, proximity of wiring to primary and back-up flight controls, presence of combustible materials, and potential for accidental damage to wiring.
Appendix
C. Figure 1. Determination if SB modification or STC requires EZAP
Explanation of Steps
Step 1: Does the SB or STC affect or modify wiring or it’s environment?
The question asks whether the STC affects or modifies wiring. Modifications to wiring or other EWIS components include, but are not limited to removal, addition, relocation, etc.
Does the SB or STC install or result in wiring being located within 5 cm (2 inches) of primary and back-up hydraulic, mechanical or electric flight controls, change the density of the zone or change the potential effects of fire in the zone?
Does the SB or STC affect zone density? If the STC includes the addition or deletion of numerous components in a small area, the density of the zone could be changed even if wire bundles are untouched. A significant change in the zone density should warrant re-analysis of the zone.
Potential effects of fire on adjacent wiring and systems require the analyst to assess the potential effect of a localised fire on adjacent wiring and systems by considering the potential for loss of multiple functions to the extent that a hazard could be introduced. Consideration of potential effect must also include whether wiring is in close proximity (i.e. within 5 cm (2 inches)) to both primary and back-up flight controls.
Additionally, this question requires an evaluation of whether the zone might contain combustible material that could cause a fire to be sustained in the event of an ignition source arising in adjacent wiring. Examples include the possible presence of fuel vapours, dust/lint accumulation, and contaminated insulation blankets.
With respect to commonly used liquids (e.g. oils, hydraulic fluids, and corrosion prevention compounds), the analyst should refer to the product specification in order to assess the potential for combustibility. The product may be readily combustible only in vapour/mist form and thus an assessment is required to determine if conditions might exist in the zone for the product to be in this state.
Although liquid contamination of wiring by most synthetic oil and hydraulic fluids (e.g. skydrol) may not be considered combustible, it is a cause for concern if it occurs in a zone where contamination causes significant adherence of dust and lint.
If the answer to this question is ‘No’, then no further action is required (Step 2), since the density of the zone or the potential effects of fire in the zone has not changed.
Step 2: No further action is required.
Step 3: Perform an EZAP analysis.
If the answer to question 1 is ‘Yes’, then the only way to determine if existing EWIS maintenance tasks are sufficient is to perform the EZAP for the SB or STC and compare the results with the existing EWIS maintenance tasks (see Step 4).
Step 4: Is there an existing MRBR EZAP task(s) that is applicable and effective?
Once the SB or STC EZAP has been accomplished, a comparison of the derived maintenance tasks can be made with the existing EWIS maintenance tasks. If the existing tasks are adequate, then no further action regarding EWIS maintenance actions for the STC is necessary.
Step 5: No further action is required since the existing EZAP-derived maintenance task is adequate.
Step 6: Develop an appropriate task and incorporate it into the existing maintenance programme.
These tasks should be incorporated into the operator’s existing maintenance programme.
[Amdt 20/4]