Corrosion Control for Aircraft (Part 1 of 2)

Corrosion Protection and Control Program

Determination of the Corrosion Levels

A. Find the Corrosion Levels.

(1) Corrosion found on a structure when you use the Corrosion Program and Corrosion Prevention 7(CPCP) Baseline Program will help find the extent of the corrosion.

(2) The second and subsequent inspections will find how well the CPCP program has been prepared or if there is a need to make adjustments to the Baseline Program.

(3) A good quality CPCP is one that controls corrosion to Level 1 or better.

(4) If Level 2 corrosion is found during the second or subsequent inspection, you must do something to decrease the future corrosion to Level 1 or better.

(5) If Level 3 corrosion is found, you must also do something to decrease the future corrosion to Level 1. Also, a plan to find or prevent Level 3 corrosion in the same area on other airplanes must be added to the CPCP.

(6) All the corrosion that you can repair in the allowable damage limits, (less than 10 percent of the part thickness) is Level 1 corrosion.

(7) If all corrosion is Level 1, the CPCP is correctly prepared.

(8) If you must reinforce or replace the part because of corrosion, the corrosion is Level 2.

(9) If the part is not airworthy because of the corrosion, you must do an analysis to find out if the corrosion is Level 3.

(10) The chart found in this section will help find the level of the corrosion.

(11) The probability that the same problem will occur on another airplane is dependent on several factors such as: past maintenance history, operating environment, years in service, inspectability of the corroded area and the cause of the problem

Actions Follow Corrosion

 A. If corrosion is found, find the corrosion level, then do the necessary steps for a specific inspection.

B. If Level 1 corrosion is found during the first CPCP inspection.

(1) Repair the structure. Contact Cessna  for an approved repair procedure.

(2) Continue with the Baseline Program.

(a) Optional: Document the results of the inspection for use in validating program compliance.

C. If Level 2 corrosion is found during the first CPCP inspection.

(1) Repair the structure. Contact Cessna  for an approved repair procedure.

(2) Report the details of the corrosion you see to Cessna Aircraft Company and the DGCA.

(3) Continue to use the Baseline Program but check the corroded area carefully when you do a subsequent CPCP inspection.

(4) It is recommended that you record the results of the inspection to show compliance with the program.

D. If Level 3 corrosion is found during the first CPCP inspection.

(1) Immediately contact Cessna Aircraft Company and the DGCA of the corrosion you found. 

(2) Give sufficient information to make sure that the condition is a possible urgent airworthiness concern for your fleet. Get assistance from Cessna Support to develop a plan of action.

(3) Apply the corrosion program inspection, which includes the repair of the structure. Contact Cessna Aircraft Company for an approved repair procedure.

(4) Do a report that has the information of the findings. Refer to Corrosion Prevention And Control Program Reporting System - Description And Operation.

(5) Continue with the Baseline Program and other steps of procedure required by the DGCA. Examine this area carefully during future inspections.

E. If no corrosion is found during the second or subsequent CPCP inspection:

(1) Continue with the current Corrosion Prevention and Control Program. No adjustment of the current program is required.

(2) It is recommended that you record the results of the inspection for a possible increase of the corrosion inspection interval.

.

Corrosion Found

 If Level 1 corrosion is found on the second or subsequent CPCP inspection:

(1) Do the corrosion program inspection, which includes the repair of the structure. Contact Cessna Aircraft Company for an approved repair procedure.

(2) Continue with the Baseline Program.

(3) No adjustment of the existing program is required.

(4) It is recommended that you record the corrosion inspection number and the results of the inspection to show that the program was complied with.

 If Level 2 corrosion is found on the second or subsequent CPCP inspection:

(1) Repair the structure. Contact Cessna Aircraft Company for an approved repair procedure.

(2) Do a report that shows the information about the corrosion and send it to Cessna Aircraft Company and the FAA (or applicable regulatory authority).

(3) If corrosion damage required the removal of material just beyond the allowable limits (within 10 percent), complete a check of the other airplanes in the fleet before you change your aircraft's maintenance program.

(a) If the corrosion is typical of Level 2, use the fleet data to find what changes are required to control corrosion to Level 1 or better.

(b) If fleet damage is typically Level 1, examine the corroded area during subsequent inspections on all affected airplanes.

(c) Make changes to your aircraft's maintenance program if the typical corrosion becomes Level 2.

(4) Further evaluation by Cessna Aircraft Company is recommended for Level 2 corrosion findings that are well beyond the allowable limits and there is an airworthiness concern in which prompt action is required.

NOTE: The airworthiness concern is because of the possibility to have similar but more severe corrosion on any other airplane in the operator's fleet prior to the next scheduled inspection of that area.

 (5) Find the action required to control the corrosion to a Level 1 or better, between future successive inspections. These can include the items that follow:

(a) A structural modification, such as additional drainage.

(b) Improvements to the corrosion prevention and control inspections, such as more care and attention to corrosion removal, reapplication of protective finish, drainage path clearance.

(c) Decrease the inspection interval for additional airplanes that go into the program.

(6) Send a plan of corrective action to the FAA (or applicable regulatory authority) for approval and to Cessna Aircraft Company as needed.

(7) Use the approved plan of action.

H. If Level 3 corrosion is found on the second or subsequent CPCP inspection:

(1) Contact Cessna Aircraft Company and the FAA (or applicable regulatory authority) about the corrosion that was found.

(2) Send a plan to examine the same area on other affected airplanes in the operator's fleet.

(3) Apply the corrosion program inspection, which includes the repair of the structure. Contact Cessna Aircraft Company for an approved repair procedure.

I. Find the action needed to control the corrosion finding to Level 1 or better, between future successive inspections. These can include any or all of the following:

(1) A structural modification, such as additional drainage.

(2) Improvements to the corrosion prevention and control inspections, such as more care and attention to corrosion removal, reapplication of protective finish, drainage path clearance.

(3) A decrease in the inspection interval for additional airplanes entering the program.

J. Send a plan of corrective action to the FAA (or applicable regulator authority) for approval and Cessna Aircraft Company as needed.

K. Use the approved plan of action.

L. It is recommended that you give the details of the findings to Cessna Aircraft Company

Factors Influencing Corrosion Occurrences

                  If you find Level 2 or Level 3 corrosion, when you think about how to change your CPCP, think about the list that follows.

(1) Is there a presence of LPS-3 Heavy-Duty Rust Inhibitor?

(2) Is there a presence or condition of protective finish?

(3) What was the length of time since the last inspection and/or application of corrosion inhibiting compound?

(4) Was there inadequate clean-up/removal of corrosion prior to application of corrosion inhibiting compound, during previous maintenance of the area?

(5) Are the moisture drains blocked or is there inadequate drainage?

(6) What was the environment, the time of exposure to the environment and the use of the airplane?

(7) Was there a variation in past maintenance history and or use of the airplanes in the operator's fleet?

(8) Were there variations in the production build standard in the operator's fleet?

CPCP Baseline Program Implementation

 The Baseline Program is divided into specific inspection areas and zone locations. The inspection areas and zone locations apply to all airplanes.

 Reporting System

A. CPCP Reporting System

(1) The CPCP includes a system to report to Cessna data that will show that the Baseline Program is sufficient and, if necessary, make changes.

(2) At the start of the second Corrosion Program Inspection of each area, report all Level 2 and Level 3 Corrosion results that are listed in the Baseline Program to Cessna.

Send the Control Prevention and Control Program Damage Reporting Form to: Cessna.

 Periodic Review

A. Use the Service Difficulty Reporting System to report all Level 2 and Level 3 Corrosion results to the FAA and to Cessna. All corrosion reports received by Cessna will be reviewed to determine if the Baseline Program is adequate.

Corrosion Related Airworthiness Directives

A. Safety-related corrosion conditions transmitted by a Service Bulletin can be mandated by an Airworthiness Directive (AD).

Appendix A - Development Of The Baseline Program

A. The CPCP Baseline Program

(1) The function of the CPCP  is to give the minimum procedures necessary to prevent and control corrosion so that continued airworthiness is not at risk. The PSE's are areas where the CPCP applies.

(2) The CPCP Baseline Program consists of a Corrosion Program Inspection (CPI) and an inspection time. Each inspection is to be done in an airplane zone.

CPCP – Base Line

 Introduction: Corrosion can cause damage to the airplane's structural integrity and if it is not controlled, the airframe will carry less load than what is necessary for continued airworthiness.

(1)  A CPCP is a system to control the corrosion in the airplane's primary structure. It is not the function of the CPCP to stop all of the corrosion conditions, but to control the corrosion to a level that the airplane's continued airworthiness is not put in risk.

CPCP Function

A. The function of this document is to give the minimum procedures necessary to control the corrosion so that the continued airworthiness is not put in risk. The CPCP consists of a Corrosion Program Inspection number, the area where the inspection will be done, specified corrosion levels and the compliance time. The CPCP also includes procedures to let Cessna  and the regulatory authorities know of the findings and the data associated with Level 2 and Level 3 corrosion.

This includes the actions that were done to decrease possible corrosion in the future to Level 1.

 Baseline Program

A. The Baseline Program is part of the CPCP. It is divided into Basic Task and Inspection Interval. In this manual the Basic Tasks are referred to as the Corrosion Program Inspection. This program is to be used on all airplanes without an approved CPCP. Those who currently have a CPCP that does not control corrosion to Level 1 or better must make adjustments to the areas given in the Baseline Program.

B. Typical Airplane Zone Corrosion Program Inspection Procedures.

(1) Remove all the equipment and airplane interior (for example the insulation, covers and, upholstery) as necessary to do the corrosion inspection.

(2) Clean the areas given in the corrosion inspection before you inspect them.

(3) Do a visual inspection of all of the Principal Structural Elements (PSEs) and other structure given in the corrosion inspection for corrosion, cracking and deformation.

(a) Carefully examine the areas that show that corrosion has occurred before.

NOTE: Areas that need a careful inspection are given in the corrosion inspection.

(b) Nondestructive testing inspections or visual inspections can be needed after some disassembly if the inspection shows a bulge in the skin, corrosion under the splices or corrosion under fittings. Hidden corrosion will almost always be worse when fully exposed.

(4) Remove all of the corrosion, examine the damage and repair or replace the damaged structure.

(a) Apply a protective finish where it is required.

(b) Clean or replace the ferrous metal fasteners with oxidation.

(5) Remove blockages of foreign object debris so that the holes and clearances between parts can drain.

(6) For bare metal on any surface of the airplane, apply corrosion prevention primer, refer to the Application of Corrosion Preventative Compounds.

(a) Apply a polyurethane topcoat paint to the exterior painted surface. Refer to the manufacturer's procedures.

(7) Install the dry insulation blankets.

(8) Install the equipment and airplane interior that was removed to do the corrosion inspection.

CPCP - APPLICATION

             Corrosion can cause damage to the airplane's structural integrity and if it is not controlled, the airframe will carry less load than what is necessary for continued airworthiness.

             A CPCP is a system to control the corrosion in the airplane's primary structure. It is not the function of the CPCP to stop all of the corrosion conditions, but to control the corrosion to a level that the airplane's continued airworthiness is not put in risk.Complete the initial CPCP inspection in conjunction with the first SID inspection.

 Control Prevention and Control Program Application

A. The CPCP gives the information required for each corrosion inspection. Maintenance personnel must fully know about corrosion control. The regulatory agency will give approval and monitor the CPCP for each airplane.

(1) The CPCP procedures apply to all airplanes that have exceeded the inspection interval for each location on the airplane.

(a) Cessna  recommends that the CPCP be done first on older airplanes and areas that need greater changes to the maintenance procedures to meet the necessary corrosion prevention and control requirements.

(2) Maintenance programs must include corrosion prevention and control procedures that limit corrosion to Level 1 or better on all Principal Structural Elements (PSEs) and other structure specified in the Baseline Program. If the current maintenance program includes corrosion control procedures in an inspection area and there is a report to show that corrosion is always controlled to Level 1 or better, the current inspection program can be used.

(a) The Baseline Program is not always sufficient if the airplane is operated in high humidity (severe) environments, has a corrosive cargo leakage or has had an unsatisfactory maintenance or repair. When this occurs, make adjustments to the Baseline Program until the corrosion is controlled to Level 1 or better. Refer to Section 2A-30-01, Corrosion Severity Maps, to determine the severity of potential corrosion.

(3) The CPCP consists of the corrosion inspection applied at a specified interval and, at times, a corrosion inspection interval can be listed in a Service Bulletin. For the CPCP to be applied, remove all systems, equipment and interior furnishings that prevent sufficient inspection of the structure. A nondestructive test (NDI) or a visual inspection can be necessary after some items are removed if there is an indication of hidden corrosion such as skin deformation, corrosion under splices or corrosion under fittings. Refer to the Baseline Program.

(4) The corrosion rate can change between different airplanes. This can be a result of different environments the airplane operates in, flight missions, payloads, maintenance practices (for example more than one owner), variation in rate of protective finish or coating wear.

(a) Some airplanes that operate under equivalent environments and maintenance practices can be able to extend the inspection intervals if a sufficient number of inspections do not show indications of corrosion in that area. Refer to the Glossary.

(5) Later design and/or production changes done as a result of corrosion conditions can delay the start of corrosion. Operators that have done corrosion-related Service Bulletins or the improved procedures listed in the Corrosion Program Inspection can use that specified inspection interval.

Unless the instructions tell you differently, the requirements given in this document apply to all airplanes.

(6) Another system has been added to report all Level 2 and Level 3 corrosion conditions identified during the second and each subsequent CPCP inspection. This information will be reviewed by Cessna to make sure the Baseline Program is sufficient and to change it as necessary

CPCP Basic

CORROSION PREVENTION AND CONTROL PROGRAM (CPCP)

1. Introduction

A. As the airplane ages, corrosion occurs more often, while, at the same time, other types of damage such as fatigue cracks occur. Corrosion can cause damage to the airplane's structural integrity and if it is not controlled, the airframe will carry less load than what is necessary for continued airworthiness.

(1) To help prevent this, we started a Corrosion Prevention and Control Program (CPCP). A CPCP is a system to control the corrosion in the airplane's primary structure. It is not the function of the CPCP to stop all of the corrosion conditions, but to control the corrosion to a level that the

airplane's continued airworthiness is not put in risk.

B. Complete the initial CPCP inspection in conjunction with the first SID inspection.

2. Corrosion Prevention and Control Program Objective

A. The objective of the CPCP is to help to prevent or control the corrosion so that it does not cause a risk to the continued airworthiness of the airplane.

3. Corrosion Prevention and Control Program Function

A. The function of this document is to give the minimum procedures necessary to control the corrosion so that the continued airworthiness is not put in risk. The CPCP consists of a Corrosion Program Inspection number, the area where the inspection will be done, specified corrosion levels and the compliance time. The CPCP also includes procedures to let Cessna Aircraft Company and the regulatory authorities know of the findings and the data associated with Level 2 and Level 3 corrosion.

This includes the actions that were done to decrease possible corrosion in the future to Level 1.

B. Maintenance or inspection programs need to include a good quality CPCP. The level of corrosion identified on the Principal Structural Elements (PSEs) and other structure listed in the Baseline Program will help make sure the CPCP provides good corrosion protection.

NOTE: A good quality program is one that will control all structural corrosion at Level 1 or better.

C. Corrosion Program Levels.

NOTE: In this manual the corrosion inspection tasks are referred to as the corrosion program inspection.

(1) Level 1 Corrosion.

(a) Corrosion damage occurring between successive inspection tasks, that is local and can be reworked or blended out with the allowable limit.

(b) Local corrosion damage that exceeds the allowable limit but can be attributed to an event not typical of the operator's usage or other airplanes in the same fleet (e.g., mercury spill).

(c) Operator experience has demonstrated only light corrosion between each successive corrosion task inspection; the latest corrosion inspection task results in rework or blend out that exceeds the allowable limit.

(2) Level 2 Corrosion.

(a) Level 2 corrosion occurs between two successive corrosion inspection tasks that requires a single rework or blend-out that exceeds the allowable limit. A finding of Level 2 corrosion requires repair, reinforcement or complete or partial replacement of the applicable structure.

(3) Level 3 Corrosion.

(a) Level 3 corrosion occurs during the first or subsequent accomplishments of a corrosion inspection task that the operator determines to be an urgent airworthiness concern.

4. References

A. This is a list of references for the Corrosion Prevention and Control Program.

(1) FAA Advisory Circular AC120-CPCP, Development and Implementation of Corrosion Prevention and Control Program

(2) FAA Advisory Circular AC43-4A, Corrosion Control for Aircraft

(3) Cessna Illustrated Parts Catalog - part numbers P692-12.

(4) Cessna Service Manual - part number D2064-1-13.