Appendix A STEP 4: Are there, or are there likely to be, combustible materials in zone? This question requires evaluating 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 presence of fuel vapors, dust/lint accumulation, and contaminated insulation blankets.
• With respect to commonly used liquids (for example, oils, hydraulic fluids, and corrosion prevention compounds) refer to the product specification to assess potential for combustibility. The product may be readily combustible only in vapor mist form. If so, an assessment is required to determine if conditions might exist in the zone for the product to be in this state. You should consider hydraulic fluid to be combustible in a mist form even if the product specification states that it is not combustible in its liquid state.
• Liquid contamination of wiring by most synthetic oil and hydraulic fluids (for example, skydrol) may not be considered combustible. It is a concern, however, if it occurs in a zone where dust and lint are present, because wet or oily surfaces attract dust and lint.
Assess what sources of combustible products may contaminate the zone following any single failure considered likely from in-service experience. For example, consider unshrouded pipes with connections within the zone to be potential contamination sources. Forced air ventilation in a zone tends to blow dust and lint through the air, causing it to lodge on the surfaces of wiring and other EWIS components. Wet or oily surfaces attract more dust and lint. This needs to be considered when you are assessing the possibility of a buildup of combustibles in the zone.
• Avionics and instruments located in the flight compartment and equipment bays tend to attract dust, dirt, and other contamination. Because of the heat generated by these components and their relatively tightly packed installations, you should consider that these zones have the potential for accumulating combustible material. Forced air ventilation is often used in these areas, causing lint and dust to be blown about the area and often resulting in a buildup of dust and lint on the surfaces of wiring and other EWIS components. Always use the EZAP logic for these zones. For flight compartment and equipment bays, the answer to the question in step 4 should be “yes.”
Although moisture (whether clean water or otherwise) is not combustible, its presence on wiring, or other current carrying EWIS components increases the probability of arcing from small breaches in the insulation. This could cause a localized fire in the wire bundle. The fire could spread if there are combustibles in close proximity. The risk of a sustained fire caused by moisture-induced arcing is mitigated in step 5 by identifying a task to reduce the likelihood of accumulation of combustible material on or adjacent to the wiring and other EWIS components.
STEP 5: Is there an effective task to significantly reduce the likelihood of accumulation of combustible materials? Most operator maintenance programs have not included tasks directed towards removing combustible materials from EWIS components or adjacent areas or preventing their accumulation. Evaluate whether accumulation on or adjacent to the EWIS can be significantly reduced.
Though restoration tasks such as cleaning are the most likely applicable tasks, the possibility of identifying other tasks is not eliminated. For example, a detailed inspection of a hydraulic pipe A-5
Appendix A might be appropriate if high-pressure mist from pinhole corrosion could impinge a wire bundle and the inherent zone ventilation is low. Task effectiveness criteria should include considering the potential for damaging EWIS components.
STEP 6: Define the task and assign an interval for performing it.
This step will define an applicable EWIS ICA task to reduce accumulation of combustible materials and an effective interval for performing that task. The defined task should be included as a dedicated task in the systems and powerplant section of the maintenance program. Within maintenance review board reports (MRBRs), it may be introduced under the standard practices section (ATA chapter 20 of the MRBR) with no failure effect category assigned.
Restoration tasks should not be so aggressive that they damage wiring, but should be performed at a level that significantly reduces the likelihood of combustion.
STEP 7: Is wiring close to both primary and backup hydraulic, mechanical, or electrical flight controls? This question is asked to ensure that step 8 logic is applied where wiring is close (in other words, within 2 inches/50 mm) to both primary and backup hydraulic, mechanical, or electrical flight controls, even in the absence of combustible materials in the zone.
For zones where combustible materials are present (as determined in step 4), proximity is addressed in the inspection level definition portion of step 8, and this question need not be asked.
This step addresses the concern that segregation between primary and back-up flight controls may not have been consistently achieved. Even in the absence of combustible material, a localized wire arcing could prevent continued safe flight and landing if hydraulic pipes, mechanical cables, or wiring for fly-by-wire controls are routed in close proximity (within 2 inches/50 mm) to a wiring harness. In consideration of the redundancy in flight control systems, this question should be answered “yes” if both the primary and back-up system might be affected by wire arcing.
On all aircraft type designs, regardless of TC date, alterations performed by an STC holder or a field-approved repair or alteration may not have taken into account the TC holder’s design criteria. We recommend that STC holders assess whether their design changes route wires within 2 inches or 50 mm of both primary and back-up hydraulic, mechanical, or electrical flight control cables and lines. Similarly, air carriers and air operators should assess any field-approved repairs or alterations or other modifications that have been made to their airplanes to identify any added or altered wiring that may be close to flight control cable and lines.
STEP 8: Select EWIS inspection level and interval (Figure 2).
a. Inspection Level. At this point in the analysis, it is already confirmed that EWIS is installed in a zone where the presence of combustible materials is possible and/or the wiring is in close proximity to primary and backup hydraulic or mechanical flight controls.
Therefore, some level of inspection of the EWIS in the zone is required. This step details how to select the proper level of inspection and interval.
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Appendix A
The inspection level and its interval are determined by using ratings tables, which rate characteristics of the zone and how the EWIS is affected by, or can affect, those attributes.
The type of inspection is determined by using the rating tables of EZAP Worksheet 3A (or 3B for airplane models without a dedicated zonal inspection program (ZIP)), whereas the interval for performing the inspection is determined using the rating tables of EZAP Worksheet 4.
Worksheets 3A and 3B use zone size, zone density, and the potential effect of fire in the zone to determine the type of inspection that is necessary.
• Zone size—Zone size determination is based on comparing all the zones in a given airplane model and assessing them in relation to each other. For the purposes of the EZAP analysis, zone sizes are identified as small, medium, or large. For example, the aft cargo bay on a large transport category airplane would be considered a large zone, but the radome on the same airplane would be considered a small zone. The smaller the zone and the less congested it is, the more likely it is that wiring degradation will be identified by a general visual inspection (GVI).
• Zone density—The density of installed equipment, including wiring and other EWIS components, within the zone is assessed in relation to the size of the zone. For the purposes of the EZAP analysis, zone density is identified as low, medium, or high.
Typical factors to consider are the number of components, their relative closeness to one another, and the complexity of these components (for example, multiple electrical, mechanical, or hydraulic connections). For example, the electrical and electronics compartment located in the forward nose section, below the flight deck of most large transport category airplanes, could be considered a high density zone. This is because the relatively small physical area is crowded with avionics equipment and a large number of wires and other EWIS components. An example of a low density zone on some airplanes is the cargo compartment (as defined by the cargo compartment walls and forward and rear bulkheads). Although this is a large zone relative to other zones on the airplane, it has relatively few systems or EWIS components installed in it.
• Potential effects of fire on adjacent EWIS or systems—This question should be answered from the point of view that a fire has occurred. So the question to be answered is what is the effect on the safe operation of the airplane should a fire occur.
This assessment should include consideration of the potential for loss of multiple functions and the resulting effect on continued safe operation of the airplane. The presence of flammable fluids should also be considered, although design features such as shrouds over the fuel line can be considered to mitigate the likelihood that the fuel will be a source of fuel for a fire. Base the determination of potential effects of a fire on adjacent wiring and systems on knowledge of what airplane systems are in the area under analysis (in other words, what is in the zone) and how loss or degradation of these systems could affect safe operation. The rating system developed should take these potential effects into account.
If a zone does not have mitigating design features that would reduce the adverse effects of a fire, then the potential effects of a fire should be rated higher (for example, A-7
Appendix A medium or high). Credit for fire mitigation capability can be given to zones that contain a fire detection and suppression system, or a zone that is designated a “fire zone.” Potential effects of a fire in such zones could then possibly be rated at a lower level. Consideration can also be given to whether the fire could be easily detected by crewmembers or passengers and to whether, if there was a fire, it could be extinguished or controlled by available means. Fire can result in severe outcomes, such as wire-to-structure or wire-to-wire shorting and arcing, in areas such as the cockpit, electrical power centers, and those that contain power feeder cables, which are subject to chafing, if they have flammable materials close by. A fire in these areas could present a high risk to continued safe flight and landing.
Potential effects of fire must also be considered when wiring is in close proximity (within 2 inches/50 mm) to both primary and backup flight controls. A GVI alone may not be adequate if a fire caused by failure of the wiring poses a risk to aircraft controllability.
At minimum, all EWIS in the zone will require a GVI at a common interval. For operators with a ZIP, this may be defined as a zonal GVI. For operators without a ZIP, it is a GVI of all EWIS in the zone.
The logic in figure 2 begins by asking a question:
• For airplane models with a ZIP, the logic asks: “Is zonal GVI alone effective for all EWIS in the zone?”
• For airplane models without a ZIP, the logic asks: “Is a GVI of all EWIS in the zone at the same interval effective for all EWIS in the zone?”
This step calls for consideration of whether there are specific items or areas in the zone that are more vulnerable to damage or contamination than others and thus may warrant a closer or more frequent inspection.
Such a determination could result in selection of a more frequent GVI, a stand-alone GVI (for operators with a zonal inspection program), or even a detailed inspection (DET). The intent is to select a DET of EWIS only when it is determined that a GVI will not be adequate. The person performing the EZAP should avoid unnecessarily selecting DET where a stand-alone GVI is adequate. Over-use of DET dilutes the effectiveness of the inspection.
The level of inspection required may be influenced by tasks identified in step 5 and step 6.
For example, if you have selected a cleaning task in step 5 and step 6 that will minimize accumulation of combustible materials in the zone, this may justify selecting a stand-alone GVI instead of a DET for the wiring in the zone.
b. Selecting an Inspection Interval. The inspection interval is determined by using a rating system that rates the likelihood of accidental damage and the hostility of environmental factors.
A-8
Appendix A The rating tables are designed to define increasing inspection frequency based on increasing risk of accidental damage and increasing severity of the local environment within the zone.
Refer to EZAP Worksheet 4 in this appendix.
The example “Interval Determination” table on EZAP Worksheet 4 provides a range of intervals you can choose from. Please note that these intervals are only an example. The particular intervals chosen should be compatible with the interval framework used in the existing maintenance or inspection program as detailed in the current MRBR. Your choice of interval should be based on the reasons for assigning specific rating values for hostility of environment and likelihood of accidental damage. You should also use your knowledge of the types of EWIS components to be inspected.
As an example, for a hostility of environment rating of 3 and a likelihood of accidental damage rating of 3, the table gives a range of inspection intervals. It says that the inspection should occur as frequently as every A check but the interval could be as long as once every 1C check. You should base your choice on the reasons that a 3 rating was assigned.
• The importance of assessing likelihood of accidental damage is that the higher the likelihood of accidental damage from multiple sources, the more frequent the inspection task should be. If, on the other hand, all of the factors except one have been rated as a 1, then the inspection interval could be somewhat longer.
• The choice of the inspection interval should also be based on what type of environment the EWIS is located in. Just as with the ratings for likelihood of accidental damage, the more the EWIS is exposed to various harsh environmental conditions, the more frequent the inspection interval should be. You should consider the assigned ratings from both of these tables—“Hostility of Environment” and “Likelihood of Accidental Damage”—and use sound maintenance judgment to assign the inspection task interval.
The selection of inspection tasks possible in this step is specific to whether the maintenance program includes a zonal inspection program (ZIP) or not.
For ZIP programs, the possible inspection tasks are:
• Zonal GVI
• Stand-alone GVI
• DET For non-ZIP programs, the possible inspection tasks are:
• GVI
• DET At the conclusion of this step you will have determined the required inspection level and interval for wiring in the zone. Task consolidation in step 9 allows consideration of whether A-9
Appendix A an inspection selected as a result of this analysis can be considered accomplished as part of the existing maintenance program.
STEP 9: Consider consolidation with existing inspection tasks in systems and powerplant and/or zonal programs.
This step in the procedure examines the potential for consolidation between the tasks derived from the EZAP and inspections that already exist in the maintenance program. Consolidation would require that the inspections in the existing maintenance program are performed in accordance with the inspection definitions provided in this AC. Consolidation with the fuel tank ICA is required by § 26.11(b) where possible. Compare new tasks identified by the EZAP logic against existing tasks in the maintenance program to ensure that:
a. Tasks are compatible with each other. Existing maintenance tasks and EZAP-generated inspection or maintenance tasks (such as restoration tasks) should not compromise or negate each other. For example, an EZAP-generated task should not compromise existing fuel tank system wire maintenance requirements (for example, those generated by SFAR 88) such as separation or configuration specifications.
b. Task intervals are aligned to the maximum extent possible so undue disturbance of EWIS and other systems located within the zone does not occur. However, the inspection interval you choose must ensure that the intent and reason for the EWIS inspection is not compromised. The EZAP-generated task interval is determined by completing EZAP Worksheet 4 in this appendix.
Example:
Results of the EZAP for a particular zone indicate that using an existing zonal GVI is an effective inspection task for all of the EWIS in the zone. The analysis should be continued to determine the appropriate inspection interval (EZAP Worksheet 4). If the results of the analysis contained on EZAP Worksheet 4 indicate that the EWIS inspection interval is greater than the interval for the existing zonal GVI, the existing zonal GVI interval should be used for the EZAP-identified inspection task. The existing zonal GVI interval cannot be escalated solely based on results of the EZAP analysis. The EZAP only analyzes the need for inspection type and frequency for EWIS within a zone. It does not analyze all of the systems in the zone. Therefore, its results cannot be used as the sole reason to escalate an existing zonal inspection task.
c. Redundant (or duplicate) tasks are consolidated into a single task.
For inspection programs that include a zonal inspection program (ZIP):
• You should not adjust the interval of the stand-alone inspection to match the interval of the existing zonal inspection solely for the purposes of aligning the separate task intervals. Task intervals should only be aligned if the interval will ensure that the safety objectives of identifying the stand-alone GVI in the first place can be met. One A-10
Appendix A of the criteria for considering task interval alignment is access requirements for the zone. Task intervals should be aligned to the maximum extent possible so undue disturbance of EWIS and other systems located within the zone does not occur. If a task is aligned with an existing zonal inspection, it must be identified as an EZAP-related task to prevent the possibility that it could be deleted or inappropriately escalated.
• Stand-alone GVIs and DETs identified by the EZAP should not be consolidated into the ZIP. They must be introduced and retained as dedicated tasks in the scheduled maintenance program under ATA 20 (the ATA category for electrical wiring), or ATA 28 in the case of combined SFAR 88 and EWIS inspection tasks. These tasks, along with tasks identified to reduce accumulation of combustible materials (known as cleaning or restoration tasks), should be uniquely identified to ensure they are not consolidated into the zonal program or deleted during future program development.
Within Maintenance-Steering-Group-3-based MRBRs, these may be introduced under ATA 20 with no failure effect category assigned. While a stand-alone GVI and a DET cannot be combined with existing zonal inspections, the intervals for performing them should be aligned with other maintenance tasks in the zone, such as zonal GVIs, to the extent possible.
Note:
In the past, there has been some confusion about using existing zonal GVIs in lieu of EZAP- identified stand-alone GVIs. However, a zonal GVI does not satisfy the intent of a stand alone GVI. Although on the surface it may appear that the zonal GVI would accomplish the same inspection of the EWIS within a zone that a stand-alone GVI would, it does not. This is because the stand-alone GVI forces the maintenance technician to pay particular attention to the EWIS that is identified as being necessary to inspect. It is this particular attention that will help ensure that EWIS degradation issues are identified and corrected before a potential safety issue arises. While a zonal GVI is a recognized and effective inspection technique, it does not focus particular attention on EWIS or any other system or structural component within the zone and, therefore, cannot be used in lieu of a stand-alone GVI when the EZAP identifies a stand-alone GVI as necessary.
For programs without a ZIP:
Although some non-zonal inspection programs may already include some dedicated inspections of EWIS that may be equivalent to new tasks identified by an EZAP, it is expected that a significant number of new EWIS inspections will be identified for introduction as dedicated tasks in the system and powerplant program. All new tasks identified by an EZAP should be uniquely identified to ensure they are not deleted during future program development.
A-11
Appendix A For programs with or without a ZIP:
The following guide can be used for programs with or without a ZIP to determine proper consolidation between EZAP-derived inspections and existing inspections of the same item or area. When an EZAP task is selected for consolidation, the documentation should include a record identifying it for traceability purposes.
• If the EZAP inspection interval and existing inspection interval are equal, but the
inspection levels are different, the more detailed inspection takes precedence (for
example, a 1C DET takes precedence over a 1C GVI).
• If the EZAP inspection interval and existing inspection interval are different, but the inspection levels are equal, the more frequent inspection interval takes precedence (for example, a 1C GVI takes precedent over a 2C GVI).
• If the EZAP inspection interval and level are different than the existing inspection interval and level, these tasks may be consolidated using the more frequent inspection and at the more detailed level (for example, a 1C DET takes precedent over a 2C GVI). When the more frequent inspection is less detailed, the tasks should not be consolidated.
For EZAP-developed STC tasks, it may not be possible for the STC holder to determine whether a ZIP exists on specific airplane that will use the STC. If a ZIP exists, consolidation of EZAP-derived STC tasks into an operator’s ZIP will be the responsibility of the operator and should be approved by the operator’s FAA principal inspector or cognizant Flight Standards District Office (FSDO). AC 120-99, Incorporation of Electrical Wiring Interconnection System (EWIS) Instructions for Continued Airworthiness into an Operator’s Maintenance Program, will contain guidance related to this.
Note:
The more frequent inspection at the more detailed level should be used, unless it is judged that performing the more detailed inspection too frequently can result in stressing/disturbance of EWIS components.
In cases where the STC holder determines a requirement for a GVI that should not be consolidated into a ZIP, this stand-alone GVI should be specifically identified as such in the EZAP-derived ICA for the STC.
A-12
Appendix A
3. Examples of Typical EZAP Worksheets.
a. For Anyone Required to Conduct an EZAP Evaluation. The following pages contain worksheets you can use to conduct an EZAP. The first six worksheets contain notes to assist you in proper use of the worksheet. There are blank worksheets in appendix H of this AC that you can copy and use to conduct the analysis.
• EZAP Worksheet 1: Enhanced Zonal Analysis – Details of Zone
• EZAP Worksheet 2: Enhanced Zonal Analysis – Assessment of Zone Attributes
• EZAP Worksheet 3A – For Airplane Models with a Dedicated Zonal Inspection Program (ZIP): Enhanced Zonal Analysis – Inspection Level Determination Based on Zone Size, Density, and Potential Impact of Fire
• EZAP Worksheet 3B – For Programs without a Dedicated Zonal Inspection Program (ZIP): Enhanced Zonal Analysis – Inspection Level Determination Based on Zone Size, Density, and Potential Impact of Fire
• EZAP Worksheet 4 – Intervals Based on “A” and “C” Checks: Enhanced Zonal Analysis – Interval Determination Based on Hostility of Environment and Likelihood of Accidental Damage
• EZAP Worksheet 5: Enhanced Zonal Analysis – Task Summary A-13
EZAP WORKSHEET 1 05/04/10 Enhanced Zonal Analysis - Details of Zone (steps 1 and 2 of figure 1) Zone Number: Zone Description:
Hydraulic plumbing Comments Hydraulic component (valves, actuators, pumps) Pneumatic plumbing Pneumatic components (valves, actuators) EWIS - power feeder (high voltage, high amperage) EWIS - motor driven devices A-14 EWIS - instrumentation and monitoring Use this area to describe the zone location, access, and boundaries. List the content of the zone such as installed equipment, wiring, other EWIS EWIS - data bus components, plumbing, components. Also note significant EWIS related items. Examples: "Wire bundle routed within 2 inches of high-temperature Electrical components anti-ice ducting." or "Zone contains IDG, RAT, APU and forward galley Primary flight control mechanisms power feeder cables."
Secondary flight control mechanisms The intent of the description is to provide the analyst with a clear understanding of what is in the zone and how it could potentially affect Engine control mechanisms wiring and other EWIS components within the zone.
Fuel system components Insulation Oxygen system components Potable water system components Appendix A AC 25-27A Waste water system components
EZAP WORKSHEET 2 05/04/10 Enhanced Zonal Analysis - Assessment of Zone Attributes (steps 3 through 7 of figure 1) Zone Number: Zone Description:
Answers and Explanations NO (Notes: Steps 1 & 2 Completed on worksheet 1)
3. Does the zone No further action is contain EWIS? YES necessary
3.
If the answer to the questions contained in step 3 and step 7 is "NO," then no further analysis is necessary.
NO . Is wiring or other NO
4. Are there, or are there EWIS components If the answer to question 5 is "YES" and a task is J likely to be, close to both primary identified that can significantly reduce the ur combustibles in the YES AND back-up hydraulic, YES likelihood of accumulation of combustible zone? mechanical, or electrical materials, the task and interval must be defined in flight controls? step 6. If the task identified is a cleaning (restoration) task to remove dust/lint accumulation from wiring, other EWIS components, and/or other
5. items within the zone, the interval for the task must be frequent enough to keep the zone, including the
5. Is there an effective task to significantly NO 8. EWIS inspection tasks determination. of accumulation of dust/lint on the EWIS and other EWIS, relatively clean based on the expected rate reduce the likelihood of accumulation of YES See worksheets 3A and 3B components components within the zone.
combustible materials? In all cases, after step 5 and/or step 6, the analysis
6. is continued to step 8.
6. Define task and interval. List on Continue the analysis Appendix A AC 25-27A worksheet 5, Task Summary area
EZAP WORKSHEET 3A - For Airplane Models with a Dedicated Zonal Inspection Program (ZIP) 05/04/10 Enhanced Zonal Analysis - Inspection Level Determination Based on Zone Size, Density, and Potential Impact of Fire (step 8 of figure 1, refer to figure 2) Zone Number: Zone Description:
Density / Zone Size —→ Zone Size Inspection Level Determination Based on Potential Effect of Fire in the Zone
• Assessment Small Medium Large Size / Density Factor 1 2 3 Low 1 2 3 Low Zonal GVI Zonal GVI Zonal GVI Density Medium 2 2 3 Potential Zonal GVI + Zonal GVI + Effects of Fire Medium Zonal GVI stand-alone GVI of stand-alone GVI of in the Zone some EWIS some EWIS High 2 3 Zonal GVI + Zonal GVI + Zonal GVI + High stand-alone GVI of stand-alone GVI and/or stand-alone GVI and/or some EWIS DET of some EWIS DET of some EWIS Circle appropriate result & insert below Circle appropriate result and answer questions in the boxes below RESULT YES Answers and Explanations
1. Is a Zonal GVI alone 2. List zone effective for the entire description and zone?* boundaries for Zonal - The tables on this worksheet are used to select the appropriate level of inspection for the EWIS in the zone GVI based on an assessment of zone size, density, and potential effects of fire in the zone.
This worksheet assumes the existing maintenance program already includes a dedicated zonal inspection program. It is assumed that an existing ZIP already includes a zonal GVT of all zones that contain wiring Define specific and other EWIS components, and that the inspection of the EWIS is included in the zonal GVI.
items/areas in the 2 Zonal GVI must be zone for which a If existing zonal GVI is an effective inspection task for all of the EWIS in the zone, the analysis must be augmented with a Stand-alone GVI is continued to determine the appropriate inspection interval (worksheet 4). During task consolidation afler stand-alone GVI justified completion of the analysis, the most frequent zonal GVI interval for the zone will take precedent.
and/or a DET inspection If the results of the analysis contained on worksheet 4 indicate that the EWIS inspection interval is greater than the interval for the existing zonal GVI, the existing zonal GVI interval cannot be escalated based
• If answer to box 1 is "YES," answer box 2 only and 4. Define specific solely on the results of the EZAP analysis.
then continue the analysis on worksheet 4 in order → zone for which a DET items/areas in the If a zonal GVI is not adequate for the EWIS in the zone, in addition to identifying the zonal GVI, the Appendix A AC 25-27A to determine the task interval. s justified 4 analyst must also identify the specific items/areas in the zone where a stand-alone GVI and'or DET inspection is necessary.
If answer to box 1 is "NO." answer boxes 2, 3, and 4 and then continue the analysis on worksheet 4 in order to determine the task interval.