CESSNA AIRCRAFT COMPANY AIRCRAFT DIVISION WICHITA, KANSAS Report No: RE-GEN-004 Rev B Reliability Substantiation and Program Requirements

Transcription

1 CESSNA AIRCRAFT COMPANY AIRCRAFT DIVISION WICHITA, KANSAS Report No: Reliability Substantiation and Program Requirements DATE: October 24, 2008 Written By: Checked By: Approved By: Approved By: Original signed by Mitchell Rausch Engineer, Reliability Original signed by Stefanie Hahn Specialist, Reliability Original signed by Ken Maine Supervisor, Reliability Original signed by Glenn Jarrell Manager, Reliability

2 The Cessna Aircraft Co. Page i Revisions Rev Date By: Approved By: - 8/20/2003 Stefanie Hahn Lyle Bitker ECR No: Section All Description Initial Release Rev Date By: Approved By: A 9/8/2003 Stefanie Hahn Orhan Kunter ECR No: Section Description MTBF verbiage in referenced section Rev Date By: Approved By: B 10/24/2008 Mitchell Rausch Glenn Jarrell ECR No: Section All Description Document rewritten for clarity and content i

3 The Cessna Aircraft Co. Page ii TABLE OF CONTENTS Section Page 1. INTRODUCTION RELIABILITY SUBSTANTIATION Reliability Requirement Environmental Definition Reliability Substantiation Methods Cessna Field Service History Substantiation by Similarity Other OEM Service History Testing Reliability Demonstration Test Accelerated Life Testing HALT Test Report Failure Reporting Procedure Reliability Substantiation Deliverables PRODUCTION AND FIELD SUPPORT PROCEDURES Introduction Production Support Reliability Screening Production Failure Reporting Production Corrective Action Field Support Reliability Performance No Fault Found (NFF) Policy Reliability Corrective Action Procedure Production and Field Support Deliverables... 9 ii

4 The Cessna Aircraft Co. Acronyms and Definitions Page iii B10 Life The time at which 10% of the population will fail. CONFIRMED FAILURE A failure which has been verified by the supplier or the authorized authority. FAILURE The inability of product(s) to operate within the specified performance levels. FAILURE ANALYSIS The process in which a reported failure is evaluated to determine the root cause of the failure. Reliability physics is utilized to identify the failure mechanisms of a failed part or material through physical, chemical, and/or electrical failure analysis techniques. Root cause determination seeks to go beyond the symptomatic defect and, when successful, identifies and corrects the basic underlying part or process problem. FLIGHT HOURS The accumulated time intervals between wheels-off and wheels-on. LINE REPLACEABLE UNIT (LRU) A unit which can be readily changed on an aircraft in accordance with published line maintenance manuals. MEAN TIME BETWEEN FAILURE (MTBF) A reliability performance measure calculated by dividing the total unit flight hours accrued in a period, of a representative sample of units, by the number of confirmed failures that occurred during the same period. MEAN TIME BETWEEN UNSCHEDULED REMOVAL (MTBUR) A reliability performance measure calculated by dividing the total unit flight hours accumulated on the sample population, by the number of unscheduled removals that occurred during the same period. An MTBUR calculation assumes a constant unscheduled removal rate. RELIABILITY Probability that a component or system will perform its intended function within a specified environment for a specific period of time. R & I Removal and installation time associated with a component or product. UNIT FLIGHT HOURS The accumulated flight hours of all like units installed in an aircraft during a specified reporting period. iii

5 The Cessna Aircraft Co. Page iv UNSCHEDULED REMOVAL The removal of a unit brought about as a result of a known or suspected malfunction and/or defect in the unit. WEIBULL MEAN LIFE Statistical measure that is calculated using the shape parameter (β) and characteristic life (η) of the Weibull distribution and the Gamma function. For the special case when β = 1, the Weibull mean life is equal to the cumulative hours divided by the number of unscheduled removals. iv

6 The Cessna Aircraft Co. Page 1 1. INTRODUCTION The objective of this document is to define the requirements and expectations for reliability substantiation, manufacturing, and field support. This document details key engineering and business activities that must be completed by a supplier throughout component design, development, and production. The first activity includes the reliability substantiation of a new product design that will be utilized on a Cessna aircraft. The second activity involves developing appropriate manufacturing controls and field plans to ensure that the component is effectively produced and supported in the field. This overall approach ensures that Cessna components are reliable and that they contribute to overall customer satisfaction. Reliability substantiation activities ensure that contractual reliability requirements established in the Reliability Specification (RS), Specification Drawing (SD), or Product Support Agreement (PSA) are met. Effective manufacturing and field support ensures that the customer receives a product that meets the reliability requirement and is supported in the field. Manufacturing support activities include reliability screening, failure analysis, and corrective actions for components in the production flow. Field support activities include reliability tracking and a closed loop root cause and corrective action process for returned units. 2. RELIABILITY SUBSTANTIATION The supplier must demonstrate that the component meets or exceeds the reliability requirement. Reliability substantiation is accomplished when the supplier has demonstrated through field history or reliability testing that the component meets or exceeds the reliability requirement. In some instances, highly accelerated life testing (HALT) may be accepted as an alternative to quantitative substantiation. Reliability substantiation testing must be completed before qualification testing. 2.1 Reliability Requirement The reliability requirement is assigned as a means of assuring acceptable economic value and customer satisfaction. The desired performance is separate from the certification type design requirement and does not have a direct bearing on regulatory compliance. However, this requirement may meet or exceed any requirement specified by regulation. The supplier must indicate agreement with reliability requirements during the request for proposal (RFP) process. System level requirements may be provided in addition to the LRU requirements. Individual component levels must contribute to meet the system requirement. Cessna Reliability Engineering determines the appropriate statistical model to establish the reliability requirement. The majority of components installed on aircraft have a 1

7 The Cessna Aircraft Co. Page 2 predominantly random unscheduled removal rate (exponential distribution). As a result, the mean time between unscheduled removals (MTBUR) may be used as a statistical measure of reliability performance. This measure requires that no significant amount of infant mortality (early removals or high number of initial removals) or wear-out (increased removals with component age) is present in the component population. If significant infant mortality or wear-out is present, alternate means of measuring component reliability must be used. The Weibull mean life or B10 life will be utilized for components exhibiting wear-out. However, if significant infant mortality is present, a root cause and corrective action (RCCA) process must be implemented to substantially reduce the amount of infant mortality. The component field performance is provided on Supplier Tracking and Rating System (STARS), which can be accessed at Environmental Definition The Aircraft Environmental Zone Definition document, provided by Cessna for specific aircraft models in the RS, should be utilized to design and test for reliability. The supplier must consider the environmental conditions along with the mission profile when assessing reliability substantiation and test requirements. 2.3 Reliability Substantiation Methods The supplier must use one or more of the following methods, sorted in order of preference, based on the circumstances at the time of source selection. The substantiation method selected by the supplier must be provided to Cessna Reliability Engineering in the RFP response. Reference Section 2.5 Reliability Substantiation Deliverables. a) Cessna field service history b) Other OEM service history c) Test Cessna Engineering must approve the method of substantiation before supplier selection. All substantiation plans that integrate reliability testing must be submitted to Cessna Design and Reliability Engineering for approval. Reliability substantiation schedules must align with the Cessna development schedule. The reliability substantiation schedule chronicles substantiation plans, testing, and committed completion dates that must occur before qualification. Risk elements that could impede or impact the supplier s commitment to complete the reliability substantiation by the commitment dates should be identified and mitigated in the schedule. Reference Section 2.5 Reliability Substantiation Deliverables Cessna Field Service History Cessna field service history provides a means to substantiate reliability from field data on existing Cessna production aircraft. The component must meet or exceed the reliability requirement to utilize this method of substantiation. Suppliers must indicate that the reliability performance of the new installation will not be negatively impacted by differences in the operational and environmental conditions. 2

8 The Cessna Aircraft Co. Page 3 If Cessna field service history is insufficient to substantiate the reliability performance, Cessna Reliability Engineering will determine the time needed to accumulate sufficient flight hours or landings. A substantiation milestone date will be set and strict monitoring of the comparative component will occur during the scheduled time frame. If the component fails to perform to the established requirement, an aggressive root cause failure analysis and corrective action initiative is required from the supplier. Additional testing may be required if sufficient hours will not be accumulated by a specified deadline Substantiation by Similarity Substantiation by similarity for a component that is a derivative or is similar to an existing component can be accomplished using field history from Cessna production aircraft. The component must meet or exceed the requirement to utilize this method of substantiation. The substantiation plan must be reviewed and approved by Cessna Design and Reliability Engineering Other OEM Service History Other OEM service history includes non-cessna field service data for substantiation. The data must be drawn from a similar aircraft operating environment. Technical data, including population or sample size, usage rate, environmental and operational conditions, number of removals, and relevant RCCA, must be supplied to Cessna Reliability Engineering to verify component application and usage. Regional or commercial aircraft data is not adequate for reliability substantiation due to different operational and maintenance practices. Data disclosure agreements must be upheld by the supplier when utilizing this substantiation method. Cessna Reliability Engineering will give the final approval to utilize other OEM service history. In most cases, the supplier will be required to perform additional substantiation testing to supplement the OEM service data Testing Testing methods acceptable by Cessna include a reliability demonstration test, accelerated life test, and HALT. A test plan must be submitted for any method of test and must align with the development schedule. Reliability substantiation testing must be completed before qualification testing. Reference Section 2.5 Reliability Substantiation Deliverables Reliability Demonstration Test The reliability demonstration test is accomplished by subjecting a near production configuration unit to the expected operational conditions over the required period of time. Cessna Design and Reliability Engineering must approve the test procedure prior to the start of the reliability substantiation test, along with the acceptability of the test unit configuration. Failures induced during testing shall be reported to Cessna within 24 hours of occurrence. Test time required for acceptable substantiation is a function of the MTBF requirement and the number of failures that occur during the test. For the purpose of testing, the 3

9 The Cessna Aircraft Co. Page 4 MTBF is 1.25 times the MTBUR as specified in the applicable RS document. Sufficient test time is required to demonstrate the MTBF with an 80% confidence level. Table 1 provides MTBF multipliers, calculated using the cumulative binomial function, to acquire the required test time given a Weibull beta, the number of test units, and the number of allowed failures. Cessna Reliability Engineering can aid in providing test factors that are not available in Table 1. The required test time represents the time that a test setup and/or test chamber will operate to complete the test, given a specified number of test units and allowed number of failures. Table 1: Required test time MTBF multipliers 80% Confidence Allowed Failures Beta # units on test The following steps can be utilized to generate the required test time. provided to demonstrate the solution procedure. An example is 4

10 The Cessna Aircraft Co. Page 5 Step 1: Identify the beta value in the left column of Table 1. Step 2: Move to the right and select the number of units on test within the beta section from Step 1. Step 3: Move across to the intersection of the test unit row and the allowed number of failures column. Step 4: Record the test factor provided in the cell from Step 3. Step 5: Multiply the test factor by the MTBF to generate the required test time. Example: Consider a component with β=1.5 and an MTBUR requirement of 4,000 hours. For the test, there are three components available for testing. One failure will be allowed during the test. Solution: A breakout of Table 1 is provided for each step of the example to promote clarity. The identified values required to solve the example for each step are in bold print. Step 1: β = 1.5 Identify the beta value in Table 1. 80% Confidence Allowed Failures Beta # units on test Step 2: Test units = 3 Identify the number of units on test in Table 1. 80% Confidence Allowed Failures Beta # units on test

11 The Cessna Aircraft Co. Page 6 Step 3: Allowed failures = 1 Identify the allowed number of failures in Table 1. Move down to the intersection of the test unit row. 80% Confidence Allowed Failures Beta # units on test Step 4: Record the test factor value of Step 5: Calculate the MTBF using MTBF = 1.25*MTBUR. The MTBF equates to 5,000 hours given a 4,000 hour MTBUR requirement. Multiply the test factor identified in Step 4 by the MTBF. Therefore, for this example, the required test time is equal to 6,419 hours Accelerated Life Testing Accelerated life testing is accomplished by subjecting a near production configuration unit to increased stresses that exceed normal operating levels. Environmental and cyclical acceleration are acceptable means to perform accelerated testing. Theoretical acceleration factors alone are not acceptable. Acceleration factors derived from test or life cycle data may be acceptable. Cessna Design and Reliability Engineering must approve any acceleration factor utilized in substantiation testing HALT HALT is used to ensure a robust design in a short time period and is not intended to define a specified reliability performance. The overall process is used to identify potential weaknesses in the design by stressing the component until failure occurs and then designing the failure out of the component thereby increasing the design margin. When the component fails during testing, a root-cause failure analysis must be performed. Failures found during HALT must be designed out of the component until the economic fundamental limit of technology is reached. Standard HALT philosophies shall be incorporated into all test plans and procedures. The goal is to test components as early as possible in the development process. Production qualification units are not required to perform HALT. Significant design changes, or corrective actions initiated to address HALT findings, should be verified with additional HALT testing. HALT chambers used for reliability substantiation purposes must have six degrees of 6

12 The Cessna Aircraft Co. Page 7 freedom vibration and liquid nitrogen cooling capability. Reference RE-GEN-003 for additional technical guidelines for HALT Test Report Results of testing must be formally documented and submitted to Cessna Design and Reliability Engineering for approval. Reference Section 2.5 Reliability Substantiation Deliverables. 2.4 Failure Reporting Procedure Failures that occur during testing or on development aircraft must be documented and reported to Cessna Design and Reliability Engineering within 24 hours of failure occurrence. Failure review meetings may be called at Cessna s discretion. If corrective action is necessary and warranted, a corrective action plan must be initiated. Cessna Engineering will actively participate in design changes and corrective actions during substantiation in coordination with the supplier. 2.5 Reliability Substantiation Deliverables Table 2: Reliability substantiation deliverables and due dates Deliverable Due Date 1 Reliability substantiation method established RFP response 2 Substantiation by similarity report RFP response (if applicable) 3 High level reliability substantiation schedule RFP response 4 Detailed reliability substantiation 30 days after source selection (Reference schedule Section 2.3) 5 Reliability test plan 60 days before the test starts and in coordination with Cessna Reliability Engineering 6 Reliability test results report 30 days after completion of testing 7 Development failure notification 24 hours after occurrence 8 Development failure report 14 days after occurrence 3. PRODUCTION AND FIELD SUPPORT PROCEDURES 3.1 Introduction Production Support governs the reliability activities during component production. The objective of reliability production activities are to detect reliability issues early and to implement corrective action to minimize reliability impact. Key activities include failure reporting, root cause failure analysis, and corrective action of production units. Field Support defines a managed business and engineering plan that focuses on measurable reliability issues of the supplier components in the field. The objective is to ensure that components meet or exceed specified reliability requirements in the operational environment. 7

13 The Cessna Aircraft Co. Page Production Support Reliability Screening Reliability screening is a proactive process to detect defects before components are shipped to Cessna. The supplier RFP response should indicate the supplier s capability and plans for conducting reliability screening and proof of screen. Where appropriate, environmental stress screening (ESS) or highly accelerated stress screening (HASS) is required to prevent infant mortality Production Failure Reporting All failures of production units that occur during testing or screening prior to shipment must be documented and available to Cessna Design and Reliability Engineering for review. The failures must be addressed in a closed loop RCCA process. Failure Review meetings may be called at Cessna s discretion Production Corrective Action A closed-loop root cause failure analysis process shall be utilized to prevent failure modes identified in the production process from reaching the end customer. In the event that a corrective action is warranted, the supplier is required to coordinate with Cessna Engineering to implement changes necessary to prevent the identified failure modes from reaching the customer. 3.3 Field Support Reliability Performance Cessna Reliability Engineering is responsible for tracking component reliability performance. Reliability information is available on and the supplier is responsible for monitoring component reliability. If the reliability performance falls below the established requirement, it is the supplier s responsibility to initiate RCCA. Cessna Engineering, Cessna Reliability, Product Support, and the supplier will coordinate as necessary to ensure that reliability issues are addressed No Fault Found (NFF) Policy NFF removals are considered as chargeable events from a reliability tracking standpoint. The supplier is expected to participate in NFF investigations. Cessna will coordinate with the supplier to determine the reasons and reduce the number of NFF removals Reliability Corrective Action Procedure Components removed from the field shall undergo failure analysis. Failure modes identified during failure analysis shall be documented and provided to Cessna Design and Reliability Engineering. When reliability performance, available on falls below the reliability requirement, the supplier and Cessna will jointly investigate to determine the root cause for the failure modes. If this review indicates the supplier is responsible, the supplier shall, at no cost to Cessna, initiate corrective action. Corrective action is considered acceptable when a business plan is agreed to by Cessna for production and field units. 8

14 The Cessna Aircraft Co. Page 9 Spare part inventory shall be updated to incorporate corrective actions. Additional consignment spares will be provided to Cessna inventory to preclude out-of-stock and aircraft-on-the-ground situations that may result from demands due to service bulletins or other field campaigns. 3.4 Production and Field Support Deliverables Table 3: Production and Field Support Deliverables Deliverable Due Date 1 ESS and HASS capabilities established RFP deliverable 2 ESS or HASS plan To be determined when applicable 3 Production corrective action plan To be determined when applicable 4 Production failure reporting To be determined when applicable 5 Field Failure Reporting To be determined when applicable 6 Field Corrective Action Plan To be determined when applicable 9