402. CORRELATION REPORT. After completion of the cell correlation program, a final report should be developed to document information necessary for subsequent engine performance and acceptance testing (e.g., test cell and engine configuration, correlation factors, performance calculations used). The final report is also useful to document a comparison of the applicant’s data to the reference data and to document any recommendations. The following should be included in the final Correlation Report.
a. A statement regarding the purpose of the correlation, including any relevant background and historical information.
b. A description of:
/g183/g32 The test cell geometry, preferably including sketches and engineering drawings /g183/g32 Correlation engine configuration, including its serial number and the bellmouth, fan exhaust nozzle, and primary exhaust nozzle areas /g183/g32 A listing of dress kit part numbers and serial numbers where possible /g183/g32 Results of the fuel sample analyses /g183/g32 Significant changes made to the test cell, dress kit, and engine since the last correlation /g183/g32 Significant changes made during the current correlation testing and the reasons for making such changes
NOTE: Detailed photographs are also useful for evaluating whether or not changes have occurred to the facility.
c. The test and performance calculation procedures used, including, where applicable, complete identification of any software programs used.
d. The analysis of the applicant’s performance data compared with the reference facility data, including the measured and corrected data and the curves for both facilities. This should also include a comparison of data between the reference and baseline facilities if the applicant used a reference facility that was not the OEM’s baseline facility.
e. The derived cell correlation factors and how they should be applied.
f. Recommendations for adopting any improvements in engine performance testing (e.g., in-service acceptance testing) that do not affect the validity of the current correlation results. This may include changes that would significantly improve the quality and dependability of future performance data, such as specific operator training, addressing deficiencies in instrument calibration procedures, instrumentation, and data documentation.
g. Conclusions, including any pertinent documentation (i.e., correspondence from the OEM, qualified consultants, DERs), that the applicant’s test cell is acceptable for specific engine model inservice acceptance testing based on the correlation analysis.
Par 402 Page 29
h. If applicable, the final report should include a statement indicating that it supersedes the previous report. The report should be made part of the facility operations manual or other similar documents, as discussed in paragraph 404 below.
403. MAINTAINING CORRELATION. Once a test cell correlation has been established, it must be satisfactorily maintained. Maintaining correlation relies on recognizing elements that could adversely affect the correlation. Care must be taken to control repairs and/or modifications to the test cell and/or engine test hardware (e.g., test cell inlet and exhaust airflow, thrust stand, measurement systems, data reduction software and procedures, configuration of the engines to be tested). Changes in any of these areas may affect correlation validity. This section provides information on the quality control aspects of test cell testing; how correlation can be satisfactorily maintained; items that may affect satisfactory correlation status; and good facility maintenance practices.
a. Configuration Control. Routine acceptance testing of engines following correlation should be accomplished utilizing an engine test hardware configuration that is consistent with that used for the correlation run, unless otherwise checked out as described in paragraph 305j.
(1) It is extremely important that any items affecting airflow in or around the engine or in the test cell be of the same configuration as that used for correlation testing (e.g., the bellmouth, nacelle, substitute fan reverser, bifurcated ducts, core cowl doors, applicable exhaust nozzle(s), and plugs).
Engine components projecting into the airflow, such as generators or hydraulic pumps, should also be of the same configuration. Each piece of critical test hardware must be serialized or otherwise identified. In the event that multiple sets of test hardware are used, back-to-back testing with each specific hardware configuration should be performed. Depending on the results, a separate correlation for each configuration may be required. Paragraph 403c(3) below describes back-to-back testing.
(2) Engine models using ancillary equipment projecting into the cell airflow should be identified at the time of correlation. If it is intended (or just possible) to run the engine with or without such equipment, correlation runs of the engine with and without the equipment should be performed.
b. Correlation Monitoring and Maintenance. The following paragraphs give several ways to maintain correlation. If an operator does not utilize any of the following recommended trending, periodic checks, and recorrelation testing, then it is recommended that the facility institute a process of recorrelation every seven years. This recommendation is based on reference 1-2a(1) of Appendix 1.
NOTE: If the correlation of the applicant’s facility was conducted using a reference facility other than the OEM’s baseline facility (e.g., a one-away facility), using one or more of the following methods to ensure that the correlation is maintained is important.
(1) Trending is the practice of recording and plotting engine performance parameters of satisfactory acceptance engine tests. The key parameters are plotted against results obtained from similar engine tests. These results are examined for signs of performance data shifts above and beyond normal data scatter. Trending can increase confidence in the correlation validity or can alert facilities’ organizations to a possible test anomaly or an unacceptable drift of recorded performance data over an extended period of time. To be interpreted correctly, analysis of trend data must be done with knowledge of any engine internal hardware modifications that result in a change in engine performance. In these cases, evidence of a significant performance data trend would not necessarily indicate a loss of correlation.
Page 30 Par 402
(2) Re-calibration of instrumentation in a test cell must be accomplished on a regular schedule to maintain the required measurement accuracy. A system of recording and forecasting instrumentation calibration requirements should be established. As with the case of initial correlation, all instrumentation calibrations should be performed using primary or secondary standards traceable to an accepted known standard. Paragraph 301 provides additional information on instrument calibration.
(3) Continued periodic checks provide additional confidence in the current validity of the test cell correlation. Periodic check opportunities could include running an engine in another correlated test cell and checking it against run data from the test cell under evaluation or running an engine dedicated for periodic checks in the test cell under evaluation. Data error stackup should be considered in the interpretation of test results. Maximum time intervals for recorrelation may be recommended by the OEM. Additional correlations may be made on an “as needed” basis. For instance, where a test cell has undergone significant changes, recorrelation will be required. This is further discussed in paragraph 403(c).
c. Maintenance of Test Cell Correlation Following Repairs or Modifications. To monitor changes to the test cell and its systems, adequate recordkeeping of events is necessary. Records may take the form of written logs, photographs, video, and other accurate documentation media.
(1) The following are examples of items where modifications can have significant facility effects:
/g183/g32 Engine test hardware (e.g., dress kit)
/g183/g32 Facility inlet and exhaust
/g183/g32 Data acquisition: manual to automated acquisition, manual to automated reduction (calculation), and scanning, averaging, and editing
/g183/g32 Instrumentation: type, quantity, and location
/g183/g32 Thrust stand
/g183/g32 Sizable equipment changes within the cell
(2) Repairs to test cell equipment should be evaluated for possible impact on engine performance or performance measurement.
(3) Back-to-back testing is the method most frequently used to determine the effects on engine performance of a repair or modification made to either the test cell or engine test hardware. This test is accomplished by using an engine with known stable performance that is capable of operating over the engine’s entire thrust range. Before any repair or modification in the cell or to the engine test hardware is made that may affect correlation, the engine must be run through the first stage of a back-to-back test.
The test procedure may be defined by the OEM or developed by the applicant. The schedule should include all power points that would be recorded during routine acceptance testing and may include other data points. It is good practice to perform this initial test twice, at a minimum, before any repair or modification. The data from these runs should be carefully examined to determine if engine performance is stable. When stable engine performance has been established, the engine should be stored for later testing. After the repair and/or modification has been accomplished and documented, the same engine should be tested in the cell to the same schedule as initially tested. Data from these runs should be Par 403 Page 31
analyzed to determine the effect, if any, the repair and/or modification had on engine performance and, thus, any cell correlation factor(s).
(4) Total cell airflow monitoring is a useful technique for determining whether test cell changes have affected engine performance. The measurement of the airflow, pressure, and temperature distribution in front of and around the engine under test may be determined by using a hot wire anemometer, pitot-static array, or a similar system. The data obtained during the test should be compared with that obtained during the last correlation.
(5) If any of the measured parameters that have been corrected and plotted on the characteristic performance curves have changed relative to the initial test, it should be determined whether the change(s) makes sense relative to the repair and/or modification. The parameters that have changed, the magnitude of change in their values, and the direction of their change should be considered during this evaluation. If a change to any of the parameters cannot be reconciled, an analysis of the data should be performed to determine if there is an error in the data measurement (i.e., data validation). If data validation analysis is unsuccessful in reconciling parameter differences, a recorrelation should be performed. Further, if it is determined that a new correlation factor and/or a significant change to an existing correlation factor is necessary following reconciliation of all measured parameter differences, the FAA recommends that a recorrelation be performed.
d. Test Cell Equipment and Facility Maintenance. Regular inspection and maintenance of all parts of the test cell and engine dress kit are highly recommended. A maintenance schedule should be established and followed. Maintenance should include:
/g183/g32 Instrument calibration
/g183/g32 Inspection or checks of measurement systems
/g183/g32 Inspection and repair of intake and exhaust systems (e.g., splitter panels, augmentor tube)
/g183/g32 Lubrication of moving parts
/g183/g32 Activation of valves and limit switches
/g183/g32 Inspection and repair of cell structural surfaces
/g183/g32 Intake screen debris removal
/g183/g32 Exhaust cleaning
/g183/g32 Engine intake and exhaust nozzle inspections
/g183/g32 Oil system flushing
/g183/g32 Emergency system testing
/g183/g32 Personnel training
NOTE: These practices can be characterized as good housekeeping and preventive maintenance.
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404. FACILITY OPERATIONS MANUAL. An FAA-approved facility performing in-service engine acceptance testing should have in place a facility operations manual, or other document(s) acceptable to the FAA, that defines a specific set of requirements for maintaining and operating the test cell and for maintaining a satisfactory correlation status. These requirements should include, but are not limited to, the following:
a. Recordkeeping. As a minimum, facility records must conform to the requirements of part 145.
The current edition of FAA AC 145-3, Guide for Developing and Evaluating Repair Station Inspection Procedures Manuals, prescribes recommended practices for recordkeeping.
b. Test Cell Operations. The engine make, model, and configuration for each operation in the test cell should be documented. Provisions should be made for recording the dress kit hardware and serial numbers, as applicable. This dress kit should be the same configuration as the one used for correlation, unless the dress kit has otherwise been checked out as described in paragraph 305j. Facility operating procedures should be developed. The procedures should include operations under normal and emergency conditions (such as fire, engine failure, compressor stalls, etc). In addition, procedures should be developed in the event of engine operational warnings, as indicated on the test cell console, including the disposition of these warnings.
c. Facility Maintenance Procedures. A procedure must be established to record all repairs and modifications to the facility, especially those that may affect test cell operation and correlation status.
This procedure should specify that the respective FSDO be notified of any facility modifications that may affect the correlation status. Also, a procedure should be developed to ensure that facility maintenance and instrument calibration is regularly scheduled and performed and that pertinent information is recorded.
d. Quality Control Procedures. The facility must have provisions in place to maintain a satisfactory correlation status. Various options for correlation monitoring and maintenance are discussed in paragraph 403. In addition, the facility should have a system to maintain, in a current status, the following:
(1) OEM’s documents, such as a facility planning manual, if published;
(2) Service engine acceptance test procedures taken from the OEM’s Instructions for Continued Airworthiness, and pertinent specifications and Technical Orders for each model being tested;
(3) Correlation reports; and
(4) Other pertinent documents.
NOTE: The provisions and systems discussed above should be defined in a facility operations manual or other documents(s) acceptable to the FAA.
Par 404 Page 33
Appendix 1
APPENDIX 1. RELATED TEST CELL PUBLICATIONS AND MATERIALS
1-1. FAA Advisory Circulars (AC), current edition.
a. The following free ACs may be obtained from the U.S. Department of Transportation Subsequent Distribution Center, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785.
(1) AC 20-77, Use of Manufacturers’ Maintenance Manuals.
(2) AC 20-88, Guidelines on the Marking of Aircraft Powerplant Instruments (Displays).
(3) AC 20-124, Water Ingestion Testing for Turbine Powered Airplanes.
(4) AC 20-125, Water in Aviation Fuels.
(5) AC 25.939-1, Evaluating Turbine Engine Operating Characteristics.
(6) AC 33-2, Aircraft Engine Type Certification Handbook.
(7) AC 33-5, Turbine Engine Rotor Blade Containment/Durability.
(8) AC 33.65-1, Surge and Stall Characteristics of Aircraft Turbine Engines.
(9) AC 39-6, Summary of Airworthiness Directives, Announcement of Availability.
(10) AC 43-9, Maintenance Records.
(11) AC 45-3, Installation, Removal, or Change of Identification Data and Identification Plates on Aircraft Engines.
(12) AC 145-3, Guide For Developing and Evaluating Repair Station Inspection Procedures Manuals. (Note: AC 145-3 may be superceded in the near future. Use the most current edition).
b. AC 43-4, Corrosion Control for Aircraft, is for sale and is obtainable from the Superintendent of Documents, U.S. Government Printing Office, 710 North Capitol Street, NW., Washington, D.C. 20402.
1-2. Industry Documents.
a. Society of Automotive Engineers (SAE) publications may be obtained from SAE Aerospace International, 400 Commonwealth Drive, Warrendale, PA 15096.
(1) SAE Aerospace Recommended Practice (ARP) 741B, Turbofan and Turbojet Gas Turbine Engine Test Cell Correlation, Revision B. Revised 2000-12-07 (or latest revision).
(2) SAE Aerospace Information Report (AIR) No. 4869, Design Considerations for Enclosed Turbofan/Turbojet Engine Test Cells. Issued October, 1995.
(3) SAE AIR Report No. 5026, Test Cell Instrumentation. Issued November, 1996.
Appendix 1
(4) SAE ARP Report No. 4990, Turbine Flowmeter Fuel Flow Calculations. Issued September, 1997.
b. American Society for Testing and Materials (ASTM) publications may be obtained from ASTM, 100 Barr Harbour Road, Conshohocken, PA 19428.
(1) ASTM D341-89, Volume 5.01. 1990.
(2) ASTM D287, Fuel Specification, Gravity API. Latest revision.
c. DM-009, NCR No. 30165, A Derivation of Gross Thrust for a Sea Level Jet Engine Test Cell.
MacLeod, James; National Research Council of Canada. May be obtained from: National Research Council of Canada, Montreal Road, Ottawa, Ontario, Canada K1A OR6.
d. Advisory Group for Aerospace Research & Development (AGARD) publications may be obtained from 7 Rule Ancelle, 92200 Nevilly Sur Seine, France.
(1) AGARD Lecture Series No. 169, Comparative Engine Performance Measurements.
(2) AGARD Advisory Report No. 248, Propulsion and Energetics Panel Working Group 15 on the Uniform Test Programme.
Appendix 2 *FSDO or Representative of the FAA
APPENDIX 2. ENGINE TEST CELL APPROVAL SCHEDULE FLOW CHART
Perform Testing at Baseline/Reference Facility. If Witnessed by FSDO*, FSDO* Acquires Copy of Raw Data Before Leaving Applicant Notifies FSDO of Test Schedule FSDO Performs Initial Checks
- Gets Verification of Baseline/Reference Facility FAA-Approval and Traceability Data, as Applicable
- Requests and Reviews Applicant’s Instrumentation Calibration Data FSDO/ACO Provide Relevant Information to Applicant on Cell Correlation Approval Procedures FSDO Requests Aircraft Certification Office Review of Correlation Plan and Follow-On Support for Correlation Applicant Submits Correlation Plan to FSDO Applicant Submits Letter To Local Flight Standards District Office (FSDO) Requesting Test Cell Approval
Perform Testing at Applicant’s Facility. If Witnessed by FSDO*, FSDO* Acquires Copy of Raw Data Before Leaving FSDO Approves Facility and Specifies any ACO or FSDO Recommendations/Requirements FSDO Reviews Facility Operations Manual (or Other Document(s)) ACO Reviews Report and Provides Findings to FSDO FSDO Forwards Correlation Report to ACO for Review Applicant Provides Correlation Report and Facilities Operations Manual (or Other Document(s)) to FSDO for Acceptance Page 1 (and 2)
Appendix 3
APPENDIX 3. SAMPLE CORRELATION PLOTS
CORRELATION 550 600 650 700 750 800 850 900 950 4000 6000 8000 10000 12000 14000 16000 18000 20000 CORRECTED FN (Lbf)
CORRECTED EGT (DEGREES FAHRENHEIT)
APPLICANTS CALIBRATION BASELINE CALIBRATION
CORRELATION
1.6
1.8 2
2.2
2.4
2.6
2.8 3
3.2
3.4
3.6 4000 4500 5000 5500 6000 6500 7000 CORRECTED N1 (RPM) COMPRESSION RATIO, PS3/PT2
APPLICANTS CALIBRATION BASELINE CALIBRATION
Page 1 (and 2)