Subject: CORRELATION, OPERATION, 

DESIGN, AND MODIFICATION 

OF TURBOFAN/JET ENGINE

TEST CELLS 

Date: 12/26/02 

Initiated by: AFS-340

AC No: 43-207 

Change: 

1. PURPOSE. This advisory circular (AC) provides guidance regarding test cell correlation procedures 

for test cells used for in-service acceptance testing of turbofan and turbojet engines. This AC discusses 

the effects of the design, operation, and modification of a test cell and engine test hardware on engine 

performance. The AC also provides guidance on conducting, evaluating, and maintaining test cell 

correlation. Like all advisory material, this AC is not in itself mandatory and does not constitute a 

regulation. The Federal Aviation Administration (FAA) issues it to describe an acceptable means, but not 

the only means, for correlating and maintaining a satisfactory correlation status of a test cell. 

2. RELATED REGULATIONS IN TITLE 14 OF THE CODE OF FEDERAL REGULATIONS 

(14 CFR).

a. Part 1, Definitions and Abbreviations. 

b. Part 21, Certification Procedures for Products and Parts. 

c. Part 33, Airworthiness Standards: Aircraft Engines. 

d. Part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alteration. 

e. Part 121, Operating Requirements: Domestic, Flag, and Supplemental Operations. 

f. Part 135, Operating Requirements: Commuter and On Demand Operations and Rules Governing

Persons On Board Such Aircraft. 

g. Part 145, Repair Stations. 

3. RELATED READING MATERIAL. References to additional documents relating to this subject 

may be found in Appendix 1. 

/s/ James J. Ballough 

Director, Flight Standards Service

12/26/02 AC 43-207 

CONTENTS 

Page

CHAPTER 1. INTRODUCTION ................................................................................................................ 1 

100. General............................................................................................................................................ 1 

101. Background ..................................................................................................................................... 1 

102. Calibration and Correlation Standards and Methods...................................................................... 2 

103. Alternative Correlation Methods..................................................................................................... 2 

104. Definitions of Terms....................................................................................................................... 3 

CHAPTER 2. CONFIGURATION AND CONSTRUCTION .................................................................... 5 

200. General Design Considerations....................................................................................................... 5 

201. Test Cell Configurations................................................................................................................. 5 

Figure 2-1. Test Cell Configuration: “L” Type ............................................................................ 6 

Figure 2-2. Test Cell Configuration: “U” Type............................................................................ 7 

Figure 2-3. Test Cell Configuration: Folded Inlet Type............................................................... 7 

202. Engine Test Cell Major Components/Systems ............................................................................... 8

Figure 2-4. Typical Thrust Mount Design..................................................................................... 9 

CHAPTER 3. MEASUREMENT SYSTEMS, CALIBRATION, AND CORRELATION ...................... 11 

300. Measurement Systems................................................................................................................... 11 

301. Instrument Calibration .................................................................................................................. 12 

302. Thrust Calibration ......................................................................................................................... 12 

303. Factors Influencing Correlation .................................................................................................... 13 

304. Performance Measurement............................................................................................................ 13 

305. Factors Affecting Performance ..................................................................................................... 14 

306. Data Acquisition ........................................................................................................................... 18 

CHAPTER 4. TEST CELL CORRELATION........................................................................................... 21 

400. Correlation Accuracy Assurance................................................................................................... 21 

401. Correlation Procedures.................................................................................................................. 22 

402. Correlation Report......................................................................................................................... 29 

403. Maintaining Correlation................................................................................................................ 30 

404. Facility Operations Manual........................................................................................................... 33 

APPENDIX 1. RELATED TEST CELL PUBLICATIONS AND MATERIALS (2 pages) .......... 1 

APPENDIX 2. ENGINE TEST CELL APPROVAL SCHEDULE FLOW CHART (1 page)....... 1 

APPENDIX 3. SAMPLE CORRELATION PLOTS (1 page)........................................................... 1 

APPENDIX 4. GLOSSARY OF ACRONYMS AND ABBREVIATIONS (1 page) ....................... 1 

Page i (and ii) 

12/26/02 AC 43-207 

CHAPTER 1. INTRODUCTION 

100. GENERAL. This AC describes an enclosed test cell or facility, with fixed instrumentation, that is 

used for in-service acceptance testing of turbofan and turbojet engines. The AC prescribes: 

General test cell design guidelines 

Initial correlation procedures for these test cells 

Procedures that may be necessary following repairs and/or modifications to the test cell and/or 

engine test hardware 

General procedures for maintaining a satisfactory correlation status 

101. BACKGROUND. Turbine original engine manufacturers (OEM) require that their turbine engines 

be evaluated for performance and operational characteristics by engine testing following overhaul and 

certain other maintenance. The OEM’s overhaul manual specifies engine acceptance test procedures, 

parameters to be measured, and “operational” limits. The FAA requires engine maintenance and testing

in accordance with 14 CFR part 43, section 43.2(a)(2). 

a. The design and construction of turbofan/jet engine test facilities will influence engine operation 

and performance. Hardware installed on engines, such as bellmouths, thrust reversers, exhaust nozzles, 

noise suppressers, cowling, and quick engine change (QEC) components, can alter engine performance 

and influence test results. Therefore, accurate turbofan/jet engine performance evaluation requires that 

the influences of both the test facility and the engine, including its installed equipment, be known. Test 

cell correlation testing is performed to determine the effect of these items on the performance of an 

engine relative to the baseline performance of that engine. The Federal Aviation Administration (FAA) 

intends for the incorporation of the information described in this AC to provide a controlled, accurate, 

consistent, and repeatable engine acceptance test of turbofan and turbojet engines. 

b. Test cell correlation is the recommended and most common method used to demonstrate that a test 

cell is operating correctly and producing engine performance data that matches the reference or baseline 

test cell data within an acceptable small tolerance. Therefore, the correlated test cell provides a means to 

ensure that accepted engines meet minimum rated requirements. Test cell correlation factors, which may

be determined to be necessary based on the results of correlation testing, would then be applied in all 

subsequent engine acceptance testing. When a test cell is correlated for a specific engine model, the 

correlation may also be valid for derivative models of engines having lower thrust but using the same

design installed hardware. Test cell correlation procedures, pertinent to specific engine models, may be 

provided in a document published by the OEM. These correlation procedures should be specific enough 

to ensure that future in-service acceptance testing will consistently result in obtaining the required engine 

performance parameters within the manufacturer’s prescribed accuracy. When an OEM’s correlation 

documents are nonexistent or nonspecific, this AC provides information for satisfactory test cell 

correlation test procedures. 

c. Unless an acceptable alternative method is performed, test cell correlation or recorrelation should 

be accomplished under the following circumstances: 

(1) Following construction of a new test cell; 

(2) When either a new engine model or derivative model of higher (or sometimes lower) thrust is 

introduced; 

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AC 43-207 12/26/02 

(3) When repairs or structural modifications have been made to an existing test cell that 

significantly affect engine performance; 

(4) When repairs or modifications that significantly affect engine performance are made to the 

engine test hardware, as well as to the entire engine configuration (e.g., QEC, thrust reverser, bare 

engine); 

(5) When modifications have been made to existing data acquisition or data reduction systems, 

and these modifications are introduced in the test cell in a manner that could affect engine performance 

evaluation; 

(6) If and when recommended by the OEM; and 

(7) Where the FAA has determined that there is valid reason to perform a test cell correlation. 

d. Reference engine testing, which is the first stage of a correlation, is usually performed at the 

OEM’s baseline test facility. This baseline test cell is correlated or referenced to an open-air condition 

through testing using an outdoor test facility or through analysis. For various reasons, the baseline test 

facility is sometimes not available for reference testing. In this case, another facility may be used for 

reference testing. This facility must be FAA-approved and traceable to the OEM’s baseline facility. The 

use of the OEM’s test cell, which is FAA-approved for production acceptance testing of engines of the 

same type and model, is permissible for correlation reference testing.

102. CALIBRATION AND CORRELATION STANDARDS AND METHODS. Test cell correlation 

is a separate requirement beyond the calibration requirements for the test cell instrumentation. During the 

performance of instrument calibration, each instrument must be tested for conformity to an accepted 

known standard (e.g., National Institute of Standards and Technology (NIST)). In addition, a check of 

each instrument system should be performed by comparing a particular readout device and its associated 

components from the engine interface point with either a primary or secondary standard or a known input 

source.

a. Test cell correlation testing should be accomplished by operating a designated correlation engine 

that exhibits stable performance and produces at least minimum thrust. Also, it should be of the same

type and model that is to be tested in the test cell. In some cases, correlation testing may also be 

accomplished by using an engine model of a higher thrust rating to substantiate test cell utilization for 

derivative models of lower thrust. 

b. The performance of the designated correlation engine should be established by conducting

performance tests at an open-air test site or in the OEM’s baseline test cell. However, an alternative 

accepted practice is to determine the performance of the correlation engine at another FAA-approved 

facility, provided the facility is traceable to the OEM’s baseline cell. This FAA-approved facility is 

designated a “Reference Facility.” 

103. ALTERNATIVE CORRELATION METHODS. There may be test cell correlation methods 

alternative to those methods described in paragraph 102. When a facility proposes to correlate its test cell 

by procedures that deviate from the OEM’s recommendations or this AC, the facility should refer the 

proposed correlation process to its respective FAA Flight Standards District Office (FSDO). Although 

the Regulations permit an alternative means of compliance, an FAA aviation safety inspector (ASI) 

should not make this determination alone because the proper correlation of a test cell is generally an 

engineering function. Facilities correlating test cells by alternative means may receive assistance from

one or more of the following: the OEM, respective FSDO, FAA regional engineering organization, and 

Page 2 Par 101 
12/26/02 AC 43-207 

FAA Designated Engineering Representatives (DER) with knowledge and experience in engine test cell 

correlation. 

104. DEFINITIONS OF TERMS. The following are clarifications of the terms used within this AC. 

They reflect the definitions generally accepted in the industry.

a. Facility. The facility under evaluation, which is to be correlated against the reference facility. 

Also termed Applicant’s Facility. 

b. Back-to-Back Test. A test comparing performance parameters measured on the same engine in 

the same facility, typically before and after a repair or modification to a test facility and/or engine test 

hardware. 

c. Baseline Facility. A facility designated by the OEM as the standard for certification of an engine 

model. 

d. Cell Depression (Pcd). The difference between ambient barometric pressure and the static 

pressure in the test cell chamber referenced to the engine inlet. 

e. Correlation. The comparison of performance parameters measured on the same engine (i.e., 

correlation engine) tested in two individual test facilities, where one facility is the reference/baseline. 

f. Correlation Engine. An engine of known and repeatable performance, possibly equipped with 

extra instrumentation, designated to be used for test cell correlation. 

g. Correlation Factor. A multiplier or an algebraic difference that is normally used to adjust 

corrected performance parameters measured at the facility to be correlated. This adjustment accounts for 

the difference in engine performance between the facility to be correlated and the reference, or baseline, 

facility. Correlation factors are also known as correction factors or facility modifiers. 

h. Engine Dress Kit. Hardware, consisting of external engine cowling, bellmouth, exhaust nozzle, 

accessories, and test instrumentation, to facilitate engine operation in a test cell. The terms engine dress 

kit and engine test hardware are used interchangeably throughout this AC. They are intended to have the 

same meaning and may include QEC package hardware. 

i. Engine Test Hardware. See Engine Dress Kit. 

j. Instruments. Measurement and readout devices (e.g., gauges and sensors such as probes and 

pickups) used for obtaining test cell and engine operation or performance measurements. 

k. Instrument Calibration. The comparison of a particular instrument with either a primary or 

secondary (transfer) standard. The standard should be traceable to a standard maintained by NIST or 

another national standards organization. 

l. Instrument System. A system comprising a readout device and its associated components (e.g., 

sensors, interconnecting cables, tubing, fiber optics) from the engine interface point to the respective 

readout device. 

m. One-away Facility. An FAA-approved facility that is used for reference testing and has been 

correlated directly to the OEM’s baseline facility. 

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AC 43-207 12/26/02 

n. Outdoor Test Facility. An open-air facility without any enclosure for testing engines in an 

environment not influenced by man-made surroundings (e.g., walls, silencers). Not considered a test cell 

within this AC. 

o. Quick Engine Change (QEC) Kit. Engine accessory packages that permit QECs. 

p. Reference Facility. A designated test facility of known performance that is traceable to the 

OEM’s baseline facility. The reference facility is the test facility against which the facility to be 

correlated is compared. The reference facility may be the OEM’s baseline facility. 

q. Test Cell. An enclosed facility that provides a controlled environment of fixed instrumentation 

designed to evaluate turbine engine performance following overhaul or other maintenance (when 

specified by the OEM). Test cells, as defined in this AC, do not include open-air facilities, outdoor test 

facilities, or on-wing test devices.

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12/26/02 AC 43-207 

CHAPTER 2. CONFIGURATION AND CONSTRUCTION 

200. GENERAL DESIGN CONSIDERATIONS. The primary function of the engine test cell (facility) 

is to provide a controlled environment for engine testing that is compatible with the engine under test and, 

thus, will not hinder engine operation. It is therefore necessary to conduct tests in a facility that can 

accurately and consistently provide a measurement of engine performance relative to the performance that 

would have been obtained if the engine had been tested at the OEM’s baseline facility. All test facilities 

affect the testing environment and influence the data obtained during testing. This is particularly true of 

indoor test cells. An OEM’s document, such as a test cell facility planning manual, may be used as a 

design guide. If a document is not available or if the facility elects not to use it, the information contained 

in this AC may be used as a general guideline in planning and operating a test cell facility. This AC can 

be useful in evaluating the design of a test cell, troubleshooting correlation results, and in maintaining a 

satisfactory correlation status of the facility. 

a. Generally, the cell construction is of reinforced concrete for primary support structures with 

control room construction that consists of either reinforced concrete or concrete block. Secondary cell 

support areas, such as preparation rooms, may be of any industrial construction. Additional information 

on design can be found in reference 1-2(a)(2) of Appendix 1. 

b. The following system elements are common to most cell configurations. The design of these 

components may affect engine performance and data accuracy and, thus, the correlation results. 

Intake section 

Engine test and mount system section 

Augmentor/diffuser section 

Exhaust section 

Data acquisition and reduction system

Instrumentation system and control room

Engine fuel supply system

Auxiliary system (may be required by a particular powerplant being evaluated) 

201. TEST CELL CONFIGURATIONS. The presence of vortices, turbulence, and non-uniform

temperatures and pressures in the area surrounding the engine under test can drastically affect engine 

performance and test repeatability. Therefore, all test cell configurations should be designed to provide 

stable testing conditions and minimize turbulent flow by minimizing pressure loss and temperature and 

pressure variations. Under most environmental conditions, a test cell configuration should not allow 

recirculation of engine exhaust gases from the cell exhaust stack into the cell inlet. It should also prevent 

reingestion of engine exhaust gases at the rear of the engine back into the engine inlet. Test cell designs 

are typically of the following three general configurations: 

Par 200 Page 5 
AC 43-207 12/26/02 

a. “L” Type. This design has a horizontal intake and a vertical exhaust. Airflow treatment may

include at least one turning vane to turn the intake air uniformly. A grid may be installed on the 

horizontal inlet to assist with airflow straightening and provide increased noise reduction. The type “L” is 

the simplest design and the least costly to construct. A horizontal inlet will generally have good flow

distribution and a reduced Pcd when the external wind is directly entering the inlet. This configuration is 

sensitive to prevailing wind conditions and loses efficiency and repeatability when the wind changes 

direction. This configuration requires a relatively large, unobstructed test area at the engine inlet station 

for maximum performance (see Figure 2-1 for details). 

FIGURE 2-1. TEST CELL CONFIGURATION: “L” TYPE

Page 6 Par 201 
12/26/02 AC 43-207 

b. “U” Type. This design incorporates a vertical stack for both inlet and exhaust. The vertical 

intake tends to have a more uniform inlet air velocity. This design is less subject to wind disturbances. 

Airflow treatment may include at least one turning vane to turn the intake air uniformly. The inlet may be 

designed to produce a uniform airflow within the test area at the engine inlet station, as well as a uniform

engine inlet temperature. A grid may be installed on the vertical inlet to assist with airflow straightening

and provide increased noise reduction (see Figure 2-2 for details). 

Primary Test Chamber Augment or Exhaust

Screen

Test St and wit h

Thrust Frame

Inlet

Acoust ic Baffles

FIGURE 2-2. TEST CELL CONFIGURATION: “U” TYPE

c. Folded Inlet Type. This design usually incorporates vertical inlets on the building sides, resulting

in a more accessible test section because the engine entry door can be located directly in front of the 

thrust stand. Another variant of this design includes a horizontal inlet on the building top. In both cases, 

the exhaust is configured vertically. Using a series of turning vanes, the inlet air is uniformly drawn 

through a winding flow path to a large plenum, which then supplies air to the test section. This 

configuration is also not significantly affected by wind direction (see Figure 2-3 for details). 

Primary Test Chamber Augmentor Exhaust

Test Stand with

Thrust Frame

Reverse Flow Inlet

Acoustic

Baffles

Retractable

Turning

Vanes

FIGURE 2-3. TEST CELL CONFIGURATION: FOLDED INLET TYPE

Par 201 Page 7 
AC 43-207 12/26/02 

202. ENGINE TEST CELL MAJOR COMPONENTS/SYSTEMS. 

a. Engine Test Section. The engine test section is the area immediately approaching the engine 

under test. Generally, this area will be of a sufficient cross section so that the air velocity approaching the 

engine inlet will not exceed approximately 50 feet per second (fps). In this section of a well-designed test 

cell, the airflow tends to have uniform pressure distribution. Test section design and construction may

incorporate tapered or concave corners at the rear section where the air flows into the augmentor. 

b. Interior Treatment.

(1) Steep floor grades should be avoided 

(2) All drains, fittings, and other floor access areas should be flush with the floor 

(3) Floor surfaces should be clean, dry, and sealed to prevent foreign object ingestion into the 

engine and degradation of the test cell surfaces due to leakage of engine oils, jet fuel, and other 

engine-related substances. 

(4) Interior walls and ceilings should be smooth and free of protrusions. 

(5) Moveable mechanical equipment should be removed from the engine test area during testing.

c. Engine Mounts. The engine mounts support the engine during testing and permit engine thrust to 

be accurately measured. Thrust of the engine is usually produced at the engine centerline and transmitted 

through the mounts to a thrust frame. The thrust frame then pushes against or pulls on a load cell. Thus, it 

enables the reaction to be measured. 

Page 8 Par 202 
12/26/02 AC 43-207 

NOTE: The most common method of engine mounting is overhead suspension. 

However, at some engine test facilities, the engine is mounted on a pedestal 

supported by the test cell floor. The overhead mount more closely simulates the 

mounting in many aircraft, and more easily accommodates the cleaning of the 

engine test section and the accessibility of bottom-mounted engine accessories. The 

engine mount should be designed to prevent transverse motion, fishtailing, or any 

type of lateral instability. With turbofans, poor lateral stability due to mount

flexibility can result in severe engine oscillations during testing. Thrust mount

designs should also ensure that engine axial alignment is maintained during testing. 

See Figure 2-4 for a schematic representation of a typical overhead mount 

installation. 

FIGURE 2-4. TYPICAL THRUST MOUNT DESIGN 

d. Test Cell Inlet System. The test cell inlet system conditions incoming air to reduce the effects of 

wind speed, direction, and extreme temperatures. This system consists of flow straighteners, heaters, 

screens, and noise suppressers. These components tend to create a pressure loss or Pcd. The following

test cell inlet design features may have an influence on engine performance: 

Area 

Blockage

Turning angle

Axial distance between engine inlet and exit of the cell inlet 

The angle of inlet turning vanes 

Par 202 Page 9 
AC 43-207 12/26/02 

e. Test Cell Exhaust System. The test cell exhaust system augmentor removes engine exhaust gases 

from the engine test section, induces the flow of secondary air for cooling, and provides some noise 

abatement. The mix of exhaust gases and the cooling secondary airflow that goes through the augmentor 

is then directed through an exhaust stack prior to exiting the facility. The following test cell exhaust 

design features may have an influence on engine performance: 

Augmentor configuration (i.e., convergent or divergent) 

Augmentor tube length and diameter 

Exhaust inlet tube diameter 

Axial distance between engine exhaust and augmentor inlet 

Area ratio of the engine exhaust to the augmentor area 

Page 10 Par 202 
12/26/02 AC 43-207 

CHAPTER 3. MEASUREMENT SYSTEMS, CALIBRATION, AND CORRELATION 

300. MEASUREMENT SYSTEMS. The following paragraphs provide a general description of typical 

measurement systems. Instrumentation quantity, position, range, and accuracy are usually specified in an 

OEM’s document, such as a facility planning manual or overhaul manual. 

NOTE: End-to-end checks of each of the systems addressed in this section are 

extremely important to assure the validity and accuracy of the data being collected. 

These checks involve the comparison of data from a particular readout with its 

associated primary or secondary standard or with a known source. During these 

system checks, many physical, electrical, or flow discrepancies can be detected and 

corrected before correlation testing begins. 

a. Pressure Measurement Systems. Pressure measurement systems usually use simple pressure 

gauges, individual dedicated pressure transducers, or a scanning-valve system. Scanning-valve systems 

are typically a single pressure transducer that alternately measures many pressure lines of similar pressure 

range. 

NOTE: High humidity or rain drawn into the test cell can result in water getting 

into the pressure lines and producing erroneous pressure measurements for both 

types of pressure management systems. (See section 305a(2) of this AC.) 

b. Temperature Measurement Systems. Temperature measurement systems should be capable of 

independently evaluating “low and medium” and “high” temperatures. Commonly, low and medium

temperature measurement systems utilize E- or J-type thermocouples to measure engine cold section and 

facility temperatures. High temperature systems typically use K-type thermocouples to measure exhaust 

gas temperatures. The parameters to be measured will depend on the OEM’s requirements for testing. 

Thermocouple junction locations should be minimized within the test cell environment to reduce system

noise and error. 

c. Engine Speed Measurement System. The engine speed measurement system must be capable of 

measuring all engine speeds. A typical system may consist of a digital electronic frequency counter 

device and a readout device, or an analog type with a graduated display dial readout. Both systems 

provide engine speeds in revolutions per minute or percentages. 

d. Fuel Flow Measurement Systems. A typical fuel flow measurement system may consist of one 

or more turbine flow meters (or comparable flow measuring device(s)), each connected to a digital 

frequency counter and display gauge. This total measurement system, from the flow meter through the 

frequency counter to the display gauge, must be checked end-to-end for the entire operating range of the 

system. For example, a defective frequency counter could provide an acceptable error in the low flow

range, while generating a divergently increasing unacceptable error in the high range. 

NOTE: Fuel flow measurement becomes increasingly important when it is used in 

turbine gas temperature calculations. This calculation is sometimes required by 

OEMs for acceptance testing. 

e. Vibration Measurement System. Vibration is not typically evaluated during test cell correlation 

testing because it does not normally affect engine performance. However, turbine engines cannot be 

properly evaluated during in-service acceptance testing, as required by the overhaul manual, without 

employing a system to provide vibration measurement. System components can include vibration 

pickups, amplifiers, tracking filters, spectrum analyzers, band pass filters, and audio oscillators. Engine 

Par 300 Page 11 
AC 43-207 12/26/02 

pickup locations can include the fan case, intermediate case, diffuser case, and turbine exhaust case. Hot 

section vibration pickups may require insulation to prevent high-temperature damage. 

f. Trim Balance System. Although trim balancing of the low speed compressor is not required for 

test cell correlation, performing such balancing before correlation testing is acceptable. In addition, the 

OEM may specify a trim balance during in-service engine acceptance testing to determine imbalance 

moment values and, thus, the location and weights of balance counterweights. Generally, trim balancing

is accomplished with the aid of a trim balance analyzer. However, procedures are also available for trim

balancing with trial balance weights. 

g. Thrust Measurement Systems. Thrust measurement is typically accomplished by either an 

electronic strain gauge or a hydraulic measurement system. The required system accuracy should be 

specified by the OEM. 

301. INSTRUMENT CALIBRATION. 

a. Engine Test Facility. The test cell can be considered a component of an engine’s test equipment. 

As such, it requires instrumentation calibration and an end-to-end check of the measurement systems. 

Instrument calibration plus system checks ensure acceptable measurement accuracy within engine 

acceptance testing limits specified in the OEM’s overhaul manual. The OEM’s overhaul manual and 

other documents, such as a facility planning manual, reflect the procedures and test equipment that are 

required to test engines and the parameters to be measured. Test cell instrumentation must be calibrated 

and traceable to an accepted, known national standard. 

b. Standards. In the United States, the NIST represents the United States at the International 

Conference on Weights and Measurements and has the primary responsibility for maintaining the national 

and international standard units of length, mass, time, temperature, and electrical quantities. Other 

nations have comparable standards bodies. An acceptable secondary or transfer standard has been 

generally regarded as any standard that is at least four times more accurate than the accuracy requirement 

for the instrument being calibrated and is traceable to a national standard, such as those maintained by

NIST. 

c. Calibration of Instruments and a Check of Associated Systems. Calibration is used to check

an instrument’s measurements against an accepted known standard and to eliminate unacceptable 

measurement errors. Instruments should be calibrated over the expected range of operation. Periodic 

calibration of individual instruments is necessary and can be performed in place or in the instrumentation 

shop. 

d. Traceability. Traceability of each instrument calibration is important to show where all possible 

error contributions occur between the instrument and the standard. Traceability should be well 

documented. The calibration hierarchy, with inherent accuracies at each point, must be documented. 

Traceability back to a specific standard does not reduce the uncertainty of a measurement; instead, it 

provides clear documentation of the process of its determination. 

302. THRUST CALIBRATION. To calibrate the load cell, a common procedure is to apply known 

centerline forces using a centerline pull rig. This calibration procedure results in the development of a 

calibration curve of the known force and the measured load cell reaction. This curve is used during the 

correlation to obtain a true force from the load cell measurement. Another method is the use of a 

calibration device built into the thrust stand. 

Page 12 Par 300 
12/26/02 AC 43-207 

303. FACTORS INFLUENCING CORRELATION. The following factors may influence the 

correlation of an engine test cell: 

Configuration of the test cell (particularly the test cell inlet, engine test section, and augmentor 

tube and exhaust stack configurations) 

Engine position in the test cell 

Ambient conditions and surrounding area configurations 

Instrumentation (including the calibration, location, measurement accuracy, and quantity) 

Test cell thrust measurement system

Test procedures 

Data acquisition system

Fuel properties 

Cell airflow

NOTE: In addition, engine test hardware, such as cowling inlets, bellmouths, QEC

packages, cowling thrust reversers and noise suppressers, and exhaust nozzles 

installed on the engine during testing may greatly influence the data. These 

components should be serialized for tracking control. 

304. PERFORMANCE MEASUREMENT. 

a. The primary function of the engine test facility is to obtain a proper performance evaluation of an 

engine. The test facility must provide a stable test environment conducive to a smooth, surge free 

operation of the specific engine model. The environment of test facilities always has an influence on the 

test data. This is particularly true of indoor test cells. In addition, the engine test hardware configuration 

influences the test data. The combined effects of the test facility and engine test configuration on 

performance parameters are generally the reason for differences in an engine’s performance between test 

cells. The test cell correlation provides a means to: 

Quantify these differences with respect to a standard 

Understand these differences 

Eliminate or reduce these differences, whenever possible 

Establish appropriate cell correlation factors 

b. Performance Parameters. During a test cell correlation, a variety of engine performance 

parameters should be examined, including those parameters specified in the overhaul manual for engine 

acceptance testing and any values or factors used to correct primary parameters. Parameters may include, 

but are not limited to, the following: 

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AC 43-207 12/26/02 

Engine fuel flow 

Engine thrust 

Engine rotor speeds 

Engine airflows 

Engine pressures and temperatures 

Engine inlet conditions 

Test cell temperatures and pressures 

Test cell inlet airflow

Engine control systems and variable geometry

Barometric pressure 

Ambient humidity

NOTE: Sufficient data must be obtained to establish the performance of the engine. 

Secondary parameters used in the derivation of any of the above items must also be 

measured and recorded. As an example, a fuel sample should be taken during the 

test and accurately analyzed for a lower heating value (LHV) and specific gravity 

value. In addition, redundant instrumentation can be useful for data verification 

and troubleshooting purposes. 

305. FACTORS AFFECTING PERFORMANCE. To compare performance parameters between 

various test facilities or conditions within the same test facility, correcting or normalizing the 

performance parameters to common reference conditions is necessary. These reference conditions fall 

into three groups: Ambient (humidity, temperature, and pressure); fuel properties (relative density, 

viscosity, and LHV); and aerodynamic (ram pressure ratio, cell depression, and cell bypass airflow 

interaction). 

a. Humidity. While it has been recognized for a long time that high humidity levels will affect the 

performance of gas turbine engines, no consensus exists on how to handle the associated effects or 

problems. Water vapor contained in the air may have several influences on the engine and its 

performance. Although the consequences are complex, they fall into two major categories: engine inlet 

condensation and changes in engine gas properties. While the relative humidity is related to the extent of 

engine inlet condensation, the absolute or specific humidity affects the gas properties of the engine cycle 

and, hence, the performance elements.

(1) Actual condensation in an engine inlet depends on a series of factors, such as relative 

humidity, air temperature, air pressure, inlet Mach number, and dwell time. For given humidity

conditions, the probability for condensation is higher in long inlet ducts and lower in bellmouth intakes. 

Bellmouths should be sized per the OEM’s specifications. For example, an undersized bellmouth could 

result in a high local inlet Mach number that might cause inlet condensation at lower relative humidities. 

Page 14 Par 304 
12/26/02 AC 43-207 

(2) Humidity corrections for most performance parameters have been found to be small. 

However, humidity can have an impact on performance and should be considered when accurate 

performance measurements are required. To minimize this effect, some test facilities and OEMs choose 

to impose limits on test cell humidity during correlation testing for particular engine models. A relative 

humidity restriction of 75 percent is not uncommon for correlation testing.

b. Engine Inlet Temperature and Pressure. All gas turbine engines are affected by the ambient 

conditions in which they operate (primarily air temperatures and pressures). Also, engine operation and 

correlation can be affected by an engine inlet temperature distortion or gradient due to exhaust gas 

recirculation or other sources of heat. This gradient should be minimized. Unstable and low pressures in 

the test chamber or engine inlet also affect engine operation and correlation. Distorted/non-uniform cell 

airflow can cause vortices and asymmetric pressure distribution in the engine inlet. These conditions can 

also be caused by exhaust gas recirculation, poorly designed test cell inlet and test chamber sections, too 

many items protruding into the inlet airflow stream, and marginal chamber secondary airflow. In most 

cases, unacceptable temperature or pressure conditions are obvious because of their effect on engine 

performance. Their cause should be corrected to the extent possible before correlation testing.

(1) It is usually not possible to control the engine inlet air temperature and pressure to sea level, 

static, standard day values. Therefore, to compare one engine run to another, the measured engine 

performance parameters must be adjusted to the values they would have with standard day inlet air. This 

process is called normalizing or making standard day corrections to the measured data. 

(2) The method for correcting performance parameter data often varies between different engine 

types and models. The procedures to correct parameters for a particular engine model can be found in a 

specification, Technical Standard Order, or the OEM’s engine overhaul manual. 

(3) Certain primary operating variables of a gas turbine engine are normalized or corrected as 

functions of total temperature and total pressure at the engine inlet. The basic normalizing parameters are 

as follows: 

(a) θ (theta) = (observed inlet total absolute temperature) divided by (absolute temperature 

of International Standards Organization [ISO] sea level, static, standard day reference atmosphere). 

(b) δ (delta) = (observed inlet total absolute pressure) divided by (absolute pressure of ISO 

sea level, static, standard day reference atmosphere). 

NOTE: These ratios require the use of consistent units and absolute values (e.g., 

temperatures in degrees Kelvin or degrees Rankine and pressures in psia, in-HgA, 

or kPa). 

NOTE: In some cases, measured data from certain gas turbine engines are 

corrected to conditions other than ISO standard day values. In these cases, refer to 

the applicable engine model specification, Technical Standard Order, or engine 

overhaul manual. 

(4) The correction or normalizing of the major engine performance parameters requires the use 

of θ and δ, as follows: 

(a) Rotor speed, N, is normalized when divided by θx

 (i.e., N/θx) where X is dependent on 

the engine type and defined by the manufacturer (commonly, 0.5 is used). 

Par 305 Page 15 
AC 43-207 12/26/02 

(b) Thrust, F, is normalized when divided by δ (i.e., F/δ). 

(c) Airflow rate, Wa, is normalized when multiplied by √(θx/δ) (i.e., Wa√(θx

/δ)). 

(d) Fuel flow rate, Wf, is normalized when divided by δθy

 (i.e., Wf/δθy) where Y is 

dependent on the engine type and defined by the manufacturer (typical values of Y range from 0.5 to 0.7). 

(e) Engine cycle absolute temperatures (such as T3, T4, T5, and T7) are normalized when 

divided by θz

 (i.e., T5/θz) where Z is dependent on the location within the engine and the engine type. 

Z is usually defined by the OEM (typical values of Z range from 0.85 to 1.1). 

(f) Engine cycle pressures (e.g., compressor discharge, turbine discharge, nozzle exit) are 

normalized when divided by δ (i.e., P3/δ). 

NOTE: The subscripts “3, 4, 5, 7” are designators of specific axial stations in the 

engine. They are peculiar to each manufacturer. Those shown in this AC are for 

illustrative purposes only. 

c. Fuel Properties. Experience has shown that fuel selected to a particular specification from a 

single supply source maintains reasonably stable properties. However, fuel taken from various sources, 

even when selected to the same specification, can vary in properties by several percent. When comparing

fuel property data taken from different sources, the factors in the following paragraphs should be taken 

into consideration. 

(1) Fuel Relative Density. The fuel relative density, also referred to as specific gravity, may be 

utilized in the fuel flow calculation as a first order correction. Therefore, accuracy of the specific gravity

measurement is of prime importance when using volumetric flow measurement devices, such as turbine 

flowmeters. Relative density calculations are made in two steps: the relative density at a given reference 

temperature, then the relative density at the temperature of the fuel measured at the flowmeter. Relative 

density determined at the reference temperature (usually 60.0 degrees Fahrenheit [F] or 15.6 degrees 

Celsius [C], as provided within references of section 1-2 of Appendix 1 of this AC) is then corrected to 

the actual fuel temperature, using either a graph or an empirical equation. Since the relative density is a 

direct multiplier on the fuel flow, any error in the former will be transferred to the latter. 

(2) Fuel Viscosity. Depending on the type of fuel flow measuring device utilized, the viscosity

of the fuel can play a role in the calibration of that device. For example, fuel flow device calibration 

factors for Jet A/A1 and Jet B fuels are significantly different due to their differences in viscosity. Also, 

viscosity is a significant function of temperature. The specific effect can be found in the SAE ARP 

Report No. 4990, Turbine Flowmeter Fuel Flow Calculations. 

(3) Fuel Lower Heating Value.

(a) Fuel flow measurements are corrected to a common fuel LHV base. This base is 

obtained by applying the direct ratio of the fuel’s LHV to the LHV of the engine model specification or to 

the LHV of the baseline test fuel (i.e., industry standard). 

(b) Analysis of the LHV for a given batch of fuel can usually be obtained from the fuel 

supplier. An acceptable accuracy for LHV can be obtained using the aniline point gravity product method 

of a fuel sample. The determination of the aniline point and the fuel density requires a minimum of 

laboratory equipment. A more accurate fuel LHV can be determined in a laboratory by a precision bomb 

calorimeter. 

Page 16 Par 305 
12/26/02 AC 43-207 

d. Ram Pressure Ratio. Defined as the engine inlet total pressure divided by the engine exhaust 

nozzle exit static pressure, it is the result of airflow through the test cell causing pressure differences 

between the front and rear of the engine. Positive ram pressure ratio values are equivalent to flying the 

engine at a low forward velocity that affects the engine thrust. Negative ram can be deleterious to the 

operation of the engine. Since the main objective of engine test cell tests is to determine static engine 

performance corrected to sea level, static, standard day conditions, the effects of ram pressure ratio must 

be measured, documented, and accounted for in thrust determination either separately or in a correlation 

factor. 

e. Cell Depression. The difference between ambient barometric pressure and the static pressure in 

the test cell test chamber referenced to the engine inlet is known as cell depression. The difference is 

caused by pressure loss due to the velocity of air through the cell. It is usually measured in inches of 

water and denoted by Pcd. High levels of cell depression are usually a result of cell inlet or exhaust 

pressure losses. Most test cell designs result in cell depression of 2-4 inches of water, but higher or lower 

pressures may be acceptable. However, very low cell depression may result in vortices in the test 

chamber or engine exhaust gas re-ingestion into the engine inlet, causing unacceptable performance. A

very high cell depression requires a large correlation factor, may indicate inadequate airflow to the 

engine, and can cause excessive loads on the test cell walls. 

f. Cell Bypass Airflow Interactions. When a gas turbine engine is operated in an indoor test cell, its 

performance is altered because of the aerodynamic interference between the engine and the cell. In order 

to establish the thrust of the engine, the interaction of the engine with the test cell environment must be 

evaluated. Aerodynamic thrust corrections result from flow-induced forces within the test cell, which can 

be divided into three components: 

(1) Inlet momentum drag; 

(2) Structural drag on the engine and thrust stand; and 

(3) Static pressure drag along the engine. 

g. Inlet Momentum Drag. The most significant aerodynamic component of the thrust measurement 

is the inlet momentum, also known as the intrinsic inlet momentum. As a result of drawing air into the 

test cell, a force is produced on the engine. For static engine testing (i.e., non-ram facility), the magnitude 

of this force may be substantial; values from 1 to 10 percent of the measured thrust are typical. Since this 

force is, in effect, a drag term, it must be added to the measured thrust of the engine. The inlet 

momentum is a function of the engine inlet airflow and the approach airflow velocity in front of the 

engine. The approach velocity is significantly affected by the amount of cell airflow and the geometry of 

the test cell. 

h. Structural Drag. Structural drag is generated by the cell bypass airflow scrubbing the exposed 

surface area of the engine casing and pushing against the exposed structure that supports the engine on the 

thrust measurement stand. 

i. Static Pressure Drag. Local acceleration of cell bypass airflow results in static pressure gradients 

along projected surfaces of the engine, particularly the bellmouth and exhaust nozzle. These pressure 

gradients generate horizontal forces that act in a direction opposite to the measured thrust of the engine. 

Static pressure drag is sometimes broken down into the bellmouth drag and boat-tail drag. The magnitude 

of the static pressure drag is very sensitive to the cell exhaust geometry and the spacing between the 

engine exhaust and the cell exhaust system. 

Par 305 Page 17 
AC 43-207 12/26/02 

j. Dress Kit Hardware. 

(1) Engine performance is influenced by the airflow in the engine test section. Airflow 

characteristics and pressure losses in the test section are affected by protrusions in close proximity to the 

engine. Dress kit hardware, such as external engine cowling, bellmouth, exhaust nozzle, accessories, and 

test instrumentations, are examples of typical protrusions. Therefore, dress kit hardware may influence 

engine performance and the resulting correlation factor(s). 

(2) For accuracy and consistency, the part number and serial number of each dress kit hardware 

item, where appropriate, and the bellmouth, fan exhaust nozzle, and primary exhaust nozzle area 

measurements should be documented during the correlation. Engine testing at the reference and the 

applicant’s facilities are generally performed using each of their respective dress kit hardware. The dress 

kit hardware that was used during the applicant’s correlation test should be used for all subsequent tests of 

the engine model in the applicant’s test cell, unless the following applies; 

(a) If the applicant owns several sets of engine dress kit hardware, it may be necessary to 

establish correlation factors for each dress kit configuration. In this case, immediately following

correlation of the applicant’s test cell, back-to-back testing using different dress kit hardware should be 

performed to determine if any change to the correlation factor is necessary. Test configurations need to 

be documented by dress kit part number, serial number, and area measurements and matched to the 

appropriate correlation factor. 

(b) If an applicant purchases a new piece of engine dress kit hardware, a similar 

back-to-back test should be performed at that time to establish if the correlation factor needs to be 

changed. 

NOTE: Paragraph 403 describes back-to-back testing. 

306. DATA ACQUISITION.

a. A primary consideration of engine performance measurements should be data acquisition. When 

computers are not utilized in a test facility, data must be collected by visually reading and hand recording

all measured parameters on a log sheet. The use of an automatic computer-operated digital data 

acquisition system improves the accuracy of measurements and recordkeeping.

NOTE: Technology advancement in automated data acquisition systems has given 

rise to potential problem areas. Close attention should be paid to potential

problems in the planning stages of developing this type of system. Special attention 

should also be paid to cell-to-cell engine performance differences during correlation 

when a difference exists between data acquisition systems.

b. The following paragraphs contain items that may have a significant effect on test cell correlation. 

(1) Data Scan Characteristics. Computer-operated digital data acquisition systems scan, within 

a short period of time, hundreds of channels of data (e.g., temperatures, pressures, vibrations, resolver 

angles) in short, controlled bursts of repetitive signal collection. These bursts of measured data collection 

may be averaged by a computer. The following additional information is offered to provide a better 

understanding of scan characteristics. 

(a) Recommended scan characteristics may be prescribed by the OEM. 

Page 18 Par 305 
12/26/02 AC 43-207 

(b) Taking multiple scans or measurements of the same parameter will obtain a better 

average value. Due to the total interaction of the engine control system and hardware, the performance 

parameters of even a well stabilized engine slowly oscillate around a steady state average. This parameter 

oscillation may resemble a sine wave characteristic with a period possibly lasting up to several minutes. 

(c) Whether data is manually or automatically recorded, this recording process or scan takes 

a finite amount of time. With a rapid scan, the engine operating conditions change negligibly during a 

single scan period. However, with a slow scan, the sequence in which the parameters are recorded can 

influence the data quality due to time skew. Therefore, thought should be given to the recording sequence 

and parameter groupings. 

(d) The period (i.e., engine cycle) of each measured parameter should be determined either 

analytically or empirically. This information should be used in designing a scan rate for each parameter. 

Data scan techniques, including the rates, may be different for digital versus analog data acquisition 

systems. An ideal technique would be to record several points per engine cycle over a large number of 

engine cycles, so that a true average value will be calculated from the data recorded. 

(e) The oscillating engine performance discussed in paragraph 306b(1)(b) is further 

complicated by engine thermal soak-in. Soak-in is a result of the turbine mass (particularly the disks) 

slowly heating up and causing reduced turbine blade-to-shroud clearances. Thermal soak-in initiates 

immediately upon reaching a given power point and results in a real and measurable shift in engine 

performance during thermal stabilization. Soak-in can take from a few minutes to as much as 15 minutes 

for complete thermal stabilization to occur. Data acquisition should not be initiated before full thermal 

stabilization. If data acquisition is initiated before full thermal stabilization, some parameters will incur a 

real migration in the average value (i.e., a performance shift). This can be accommodated by selectively

organizing the data scan. However, as previously stated, waiting for the engine to fully soak in is more 

desirable. 

NOTE: A selectively organized data scan should read the stable parameters that are 

unaffected by thermal soak-in (i.e., most pressures and cell temperature) toward the 

beginning of the scan after a minimal soak period, but before full thermal 

stabilization occurs. Soak-affected parameters (e.g., turbine temperature, core speed, 

fuel flow, variable vane angles) should be read toward the end of the scan. 

(f) Parameters such as fuel flow, which are measured as frequency, could have significant 

errors in the calculated average value that are solely attributable to scan rate and sequencing. Therefore, 

special attention should be given to cell-to-cell engine performance differences during a correlation when 

a mismatch exists between the data acquisition systems. This could become particularly difficult when 

trying to correlate a computer-driven acquisition system against a manual or hand-logged system. 

(2) Data Averaging and Editing. Once a data acquisition methodology has been selected, an 

averaging technique should be determined. Also, a procedure pertinent to editing the data should be 

considered. These parameters are then used in the performance calculations. 

(a) Several averaging techniques can be employed. A straight average of all measured data 

is commonly performed. Alternatively, more selective techniques requiring an automatic screening of all 

data can be applied, with some data being classified as possibly erroneous. 

(b) Averaging techniques can have a significant effect on the calculated parameter average 

and, thus, the resulting performance, particularly if the engine oscillates significantly or the data were 

acquired before full thermal stabilization. Therefore, any differences between averaging methodologies 

Par 306 Page 19 
AC 43-207 12/26/02 

should be carefully considered when correlating a test cell in which different averaging techniques have

been used between the test cells. 

(c) Along with the averaging techniques employed, an appropriate editing procedure should 

be considered. Different types of editing methods can be used in conjunction with the averaging

technique chosen to produce the most representative data. Editing methods include data tolerances, 

minimum and maximum limits, and an outlier test. Editing is especially useful on multiple pressure 

readings (e.g., bellmouth static or total pressures), where line leaks can affect the validity of the data. 

Caution should be used when applying editing to parameters, such as fuel flow and engine exhaust gas 

temperatures, where editing might mask engine stability problems. When using any editing method, all 

measured data should be displayed and the edited data flagged so mismeasurements can be corrected. 

(d) The goal of data editing is to discard the erroneous data points and use only the correct 

(i.e., true) data measurements. One goal of correlation testing is to find and remedy problems in the test 

cell measurement systems. When data editing is used, there is risk that data showing a real 

mismeasurement problem may be discarded as erroneous data. If this happens, the opportunity to find 

and correct a measurement problem may be missed. 

(3) Software Verification. Computer software may be used in data acquisition and reduction. 

The FAA recommends that steps be taken to ensure that: 

(a) The appropriate software program, including version (i.e., revision), is used. 

(b) The software reflects the test requirements and performance calculations of the engine 

manual. 

(c) For a given input, the reference and applicant’s facilities produce the same output. 

(d) Data known to be valid can be used to verify the software functionality. 

Page 20 Par 306 
12/26/02 AC 43-207 

CHAPTER 4. TEST CELL CORRELATION

400. CORRELATION ACCURACY ASSURANCE. Correlation relates an engine’s performance to a 

known standard so that the performance level of the engine can be compared with established limits. 

These limits are derived from a performance baseline for a particular engine model. This baseline 

performance standard is usually the average of a number of engine tests, as established by the OEM, and 

is defined for a specific engine test hardware configuration and test facility combination. This 

combination is thereafter considered the baseline test hardware configuration and test facility for that 

particular engine model. To conduct a successful correlation program, identifying a suitable reference 

facility is necessary. It is desirable to use the OEM’s baseline test facility as the reference test facility. 

However, access to the baseline facility is not always possible. In this event, another facility may be 

designated as the reference facility. This is discussed in paragraphs 101 and 102 of this AC. 

a. Uncertainty Stackup. Additional information on determining correlation factors for the 

applicant’s facility is provided in paragraph 401e(3)(d). 

(1) If a facility not designated as the OEM’s baseline facility is used for reference testing, an 

analysis of the stackup of uncertainty of the acquired data should be performed for all correlation steps 

between the baseline facility and the applicant’s facility. The applicant’s facility correlation should be 

deemed satisfactory if this uncertainty is shown to be smaller than the OEM’s recommended acceptance 

tolerances. 

(2) As the correlation of the applicant’s facility is further removed from the baseline facility, the 

uncertainty of the applicant’s test facility accuracy tends to increase. There are measures that may be 

used to increase confidence in the correlation and reduce uncertainty to the acceptable level. The 

following examples may reduce uncertainty: 

(a) Requiring in-service acceptance limits of engines tested in the applicant’s facility to be 

less than those tolerances specified by the OEM. 

(b) Applying correlation factors to replicate the characteristics of the OEM’s baseline 

facility. 

(c) Performing multiple cross-cell tests, which is also called round-robin testing. This 

involves running one or more engines in more than one previously correlated test cell. Confidence grows 

when more engines are used and more test cells compared. 

(d) Performing multiple correlation tests between the reference and the applicant’s facilities 

to develop sufficient confidence in the correlation. This could include conducting multiple consecutive 

runs at each facility or retesting at the reference facility following testing at the applicant’s facility (which 

is referred to as A-B-A testing). 

NOTE: All of these techniques assume that an unbroken sequence of correlation 

tests exists between the baseline and the applicant’s facilities. If this sequence does 

not exist, then the correlation method described in this AC is not possible. In this 

event, efforts to substantiate that a test cell is relating engine performance back to 

the known standard will have to be found acceptable by the FAA. This is discussed 

in paragraph 103. 

b. Engine Test Hardware Configuration For Reference Testing. As previously stated, correlation 

relates an engine’s performance to a known standard for a specific engine model. This standard is defined 

Par 400 Page 21 
AC 43-207 12/26/02 

not only for testing an engine in a specific facility (i.e., the OEM’s baseline test facility), but also for 

testing a specific engine test hardware configuration (i.e., the OEM’s baseline test hardware 

configuration). 

(1) For testing at the reference facility, the FAA recommends that the engine test hardware 

configuration be the same as: 

(a) The hardware to be used during correlation testing at the applicant’s facility; 

(b) The hardware to be used for future in-service acceptance testing at the applicant’s 

facility; and 

(c) The OEM’s baseline test hardware configuration. 

(2) However, the configurations that were used during testing at the baseline, reference, and 

applicant’s facilities may be different. These differences should be evaluated for their impact on 

correlation. 

401. CORRELATION PROCEDURES. 

a. Procedure Overview. The following activities are a general overview of the step-by-step 

correlation process. Following this overview, details of these activities are discussed in paragraphs 401b 

through 401d. 

(1) Identify a correlation engine. The engine must: 

(a) Develop minimum rated thrust. 

(b) Exhibit stable performance. 

(2) Calibrate the applicant’s test cell instruments and perform an end-to-end check of systems. 

(3) Notify the respective FSDO and verify FAA-approval and the correlation status of the 

reference facility with respect to the baseline facility. 

(4) Perform a shakedown engine run at applicant’s test cell. The run will: 

(a) Verify instrumentation accuracy. 

(b) Check out all other systems. 

(5) Perform an engine test at the reference facility using the correlation engine. 

(6) Notify the respective FSDO.

NOTE: The FAA recommends that reference testing be performed before testing at 

the applicant’s facility. However, this process may be performed in reverse, if

necessary. 

(7) Perform the applicant’s facility test cell correlation. 

Page 22 Par 400 
12/26/02 AC 43-207 

(a) Notify the respective FSDO.

(b) Perform an 8- to 15-data point engine run. 

(c) Perform engine run in the same sequence and direction of approach to the test points (i.e., 

acceleration versus deceleration) as that performed at the reference facility. 

(d) Shut down the engine in preparation for an engine and facility repeatability check. 

(e) Repeat the engine test using the same procedure. 

(8) Perform a retest at the reference facility (recommended, but optional). 

(9) Perform data analysis. 

(a) Apply corrections to measured data for common reference (e.g., standard day). 

Graphically plot the data and draw a smooth characteristic line through the data for each plot. Regression 

analysis of the data is also an acceptable means of determining the characteristic line. 

(b) Analyze the data for measurement error (e.g., perform data validation). 

(c) Analyze the data for performance shift. 

(d) Determine the cell correlation factor(s) and apply to (usually) corrected common 

reference data. Plot the adjusted, corrected data. 

(e) Perform an acceptance test in accordance with the OEM’s overhaul manual to ensure the 

applicant’s test cell is capable of being utilized for satisfactory in-service acceptance testing.

(10) Develop documentation. 

(a) Write the Correlation Report, as described in paragraph 402, to document details for the 

entire correlation exercise. 

(b) Develop and document procedures for operating and maintaining the test cell and 

ensuring satisfactory maintenance of the test cell correlation status (i.e., develop a facility operations 

manual). 

b. Pre-correlation Procedure. The following activities should be performed before correlation 

testing:

(1) Determine correlation test procedures in accordance with the OEM’s correlation test 

requirements or recommendations. 

(2) Instrument the engine in accordance with the OEM’s recommendations. 

(3) Obtain fuel samples at both facilities, before or during correlation testing, and determine 

specific gravity and LHV. 

(4) Identify and record appropriate engine test hardware configuration(s) to be utilized at the 

reference and applicant’s facilities (see paragraphs 305j and 400b). Obtain measurements of the 

Par 401 Page 23 
AC 43-207 12/26/02 

bellmouth, fan exhaust nozzle, and primary exhaust nozzle areas to be used for reference and applicant 

facility testing. These measurements should be compared and may be useful when evaluating the 

correlation. Additionally, when specified by the OEM, bellmouth area measurement may be required for 

calculating airflow. 

(5) Identify an acceptable correlation engine. A new, used, or rebuilt engine can be used as long

as it demonstrates at least minimum takeoff thrust and maintains stable performance across the corrected 

thrust range from idle to takeoff. The engine’s ability to reach rated takeoff thrust without 

overtemperaturing or overspeeding is important. It allows engine testing to be performed without safety

or performance deterioration concerns. The use of an engine experiencing a gradual run-to-run variation 

in performance, such as a gradual performance deterioration, could result in a nonstandard and needlessly

complex correlation evaluation. 

(6) Immediately before the correlation run, calibrate the applicant’s test cell instrumentation and 

engine instrumentation to the selected standard. Also, perform an end-to-end check of the applicant’s 

facility measurement systems (see paragraph 301). 

(7) Notify the respective FSDO:

(a) Early in the planning process so that all requirements are identified, and 

(b) Prior to testing at both the reference and the applicant’s facility, should the FAA elect to 

witness the test. 

NOTE: If applicable, obtain proof that the reference facility is FAA-approved and

traceable to the OEM’s baseline facility. 

(8) Perform a full power shakedown run prior to the correlation run at the applicant’s facility. 

The entire facility, including the test cell, data system, and calculation procedures, should be thoroughly

tested. This may be performed with an engine other than the correlation engine. This is also another 

opportunity to investigate and eliminate facility measurement system problems, since a check of the entire 

system operating together may not have been previously performed. 

c. Correlation Procedure. The test procedure used at the applicant’s facility should be the same in 

all aspects as the procedure conducted at the reference facility. This includes: 

The number of data points acquired 

Thrust levels 

Stabilization time 

Sequence 

Direction of approach to the test points 

The parameters recorded 

Page 24 Par 401 
12/26/02 AC 43-207 

(1) Once the facility to be correlated (i.e., applicant’s facility) is thoroughly tested via the 

shakedown run, the formal correlation process can begin. In most cases, the correlation engine is first 

tested in the reference test facility. A correlation engine test usually includes 8 to 15 data points 

distributed across the thrust range. 

NOTE: Under certain conditions, fewer data points could be acceptable. 

(2) Care should be taken to fully stabilize the engine thermally and dynamically before 

data acquisition is initiated. The stabilization time should be recorded so that it can be duplicated 

during testing at the applicant’s facility. 

(3) Weather conditions should be recorded at both facilities at the time of test, as well as any

weather changes occurring during the test. It is desirable to minimize the ambient temperature and 

humidity differences between the two facilities. Any preestablished climatic envelopes are to be observed 

for satisfactory testing.

(4) To ensure consistent and repeatable engine testing, the proposed test procedure should 

include a listing of parameters to be measured and the measurement precision and range. The following

parameters should be recorded: 

Engine fuel flow 

Engine thrust 

Engine rotor speeds 

Engine airflows 

Engine pressures and temperatures 

Engine inlet conditions 

Test cell temperatures and pressures 

Test cell inlet airflow

Engine control systems and variable geometry

Barometric pressure 

Ambient humidity

NOTE: Sufficient data must be obtained to meet acceptance test procedures 

specified by the OEM. Secondary parameters used in the derivation of any of the 

above items must also be measured and recorded. In addition, redundant 

instrumentation can be useful for data verification and troubleshooting purposes. 

(5) During the engine test at the reference test facility, the sequence and direction of approach to 

the test points performed (i.e., acceleration or deceleration) should be recorded. The data points taken at 

Par 401 Page 25 
AC 43-207 12/26/02 

the facility to be correlated should also be collected in the same sequence and approach to eliminate 

performance variability due to control system hysteresis. 

(6) Once the engine test at the reference facility is complete, the correlation engine should be 

immediately preserved and shipped to the applicant’s facility for correlation testing. This will minimize

engine performance deterioration due to additional operation. 

(7) Following the initial correlation engine run at the applicant’s facility, the engine should be 

shut down for a minimum of several hours to reach a cool engine state. Time periods for cooling can 

vary; refer to the OEM’s instructions. After the shutdown period, the engine test should be repeated for 

an engine and facility repeatability check. The repeatability check is intended to demonstrate stable 

engine performance and engine run-to-run repeatability of the data measurement, acquisition, and 

reduction systems. 

(8) Ideally, the test cell correlation should include engine runs at the reference facility, at the 

applicant’s facility, and again at the reference facility (i.e., A-B-A). If the engine is routinely used for 

correlation testing, a retest at the reference facility may not be necessary if correlation engine data from

several previous runs are consistent. 

(9) Following the performance correlation runs, the correlation engine or another suitable engine 

should be tested at the applicant’s facility using the overhaul manual in-service acceptance procedures. 

This will ensure that the applicant’s facility is capable of being utilized for satisfactory engine acceptance 

testing. This should not be performed until after all correlation testing is complete and the correlation 

data has been reduced, analyzed, and accepted. 

(10) Data obtained during testing at the reference and applicant’s facilities must be recorded in a 

manual or automatic log sheet at the time of test. The FAA recommends that copies of these records be 

provided to the FAA representative witnessing the testing (if applicable) immediately upon conclusion of 

testing.

d. Post-correlation Procedure. The following paragraphs identify the post-correlation steps. The 

FAA recommends that the correlation engine be carefully stored until the correlation analysis is complete, 

in case further testing is necessary. 

(1) Following completion of correlation testing, the data must be reduced (i.e., calculations must 

be performed). Paragraph 305b describes the process of correcting or normalizing the measured data to 

sea level, static, standard day conditions. The corrected data is typically graphically displayed, and a 

smooth characteristic curve is drawn through the data. 

(2) Paragraph 401e below gives a detailed description of the post-test correlation data analysis of 

the plotted data. The OEM’s manuals and reports should also be referenced for a more thorough analysis 

description relative to a specific engine model. 

e. Correlation Data Analysis. Once engine tests at both facilities are complete (all data has been 

edited, averaged, corrected, and plotted graphically) and a smooth characteristic line has been drawn 

through the data for each performance plot, the data must be analyzed. Data analysis is an engineering

function and requires specialized knowledge. It is typically performed by the applicant, OEM, or other 

qualified personnel. It should include the following three steps: data validation with instrumentation 

error isolation, performance shift determination, and correlation factor determination. Each of these three 

elements should be isolated independently in the order given. If data errors or real performance shifts are 

not recognized, their respective effects on performance might be erroneously lumped into the third item,

Page 26 Par 401 
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the correlation factor. This could result in possible inconsistencies during future in-service acceptance 

testing of engines at the applicant’s facility. 

(1) Data Validation. Data validation analysis is the process of determining the acceptability of 

the measured, corrected data. The process of data validation requires specialized knowledge of 

standardized methods (e.g., cross-plotting of various parameters, error and cycle derivatives, influence 

coefficients) and general knowledge (preferably engine model specific) of aerodynamic/thermodynamic 

cycle effects. The following paragraphs provide some general methods of determining data validity by

analyzing the characteristic plots. 

(a) Plots should be constructed with the reference and applicant’s facility data plotted 

together for comparative analysis. Sample correlation plots are given in Appendix 3. Generally, each 

corrected parameter is plotted separately on the y-axis, while either the corrected thrust, engine pressure 

ratio (EPR), or corrected rotor speed is plotted on the x-axis of each plot. Utilizing a practice of plotting

the same ordinate (y-axis) values against another parameter, such as corrected rotor speed, is a useful way

of independently judging data validity. 

(b) Plotting each pressure ratio against corrected rotor speed can be useful in determining

possible pressure mismeasurements, though care should be taken to verify that there is not a real 

performance shift. 

(c) Once a parameter is determined to have an unacceptable error, every effort should be 

made to eliminate that error. Extensive troubleshooting of the measurement system should be performed. 

Not only should all gauges, signal conditioners, instrumentation lines, pressure probes, thermocouples, 

and rakes be carefully examined in an end-to-end check, but the data acquisition system and correction 

methodology should also be checked. Once the measurement or calculation error has been found and 

corrective action taken, a determination must be made as to whether another correlation run is necessary. 

Some errors, such as a calculation error or gauge scalar error, may be corrected without having to conduct 

another engine run. 

(2) Performance Shift Determination. 

(a) Once unacceptable measurement errors have been eliminated or compensated for, an 

assessment must be made as to whether the engine’s performance remained unchanged between the 

reference and applicant’s facilities. This can be done by cross-plotting the corrected data. If a shift in 

performance is not recognized, an incorrect correlation factor could be developed and applied to all future 

engine test data, resulting in repeated errors in assessing subsequent engine test data. 

(b) If there is an apparent performance difference between the two test runs (i.e., reference 

facility and applicant’s facility) that cannot be accounted for by expected facility and/or engine test 

configuration influences, further testing may be necessary. Follow-on actions will be determined from

the results obtained. Paragraph 303 describes factors that influence correlation. 

NOTE: Facility configuration and engine or facility instrumentation differences 

can be difficult to uncover and quantify. 

(3) Correlation Factor Determination. 

(a) Correlation factor determination should be done only after the first two parts of the 

correlation analysis (data validation and performance shift determination) have been satisfactorily

completed. 

Par 401 Page 27 
AC 43-207 12/26/02 

NOTE: Some OEMs specify run-to-run parameter tolerances for engine correlation 

testing. If the OEM’s baseline facility was used for reference testing and the data 

obtained at the two facilities was within the specified tolerances, then the applicant’s 

facility should be deemed correlated and would not require a correlation factor. See 

paragraphs 400a and 401e(3)(d) for facilities other than the baseline facility that are 

used for reference testing. 

(b) Turbofan and turbojet engines with a choked core exhaust nozzle generally require that a 

correlation factor be applied only to thrust. However, engines with unchoked core exhaust nozzles may

require additional correlation factors (e.g., exhaust gas temperature (EGT), fuel flow, rotor speeds). 

(c) OEM’s manuals should be referenced for correlation factor determination and application 

methodology. Generally, correlation factors are applied as a curve input (algebraic difference) or a scalar 

(multiplier, usually greater than unity). They also usually represent the differences in corrected data 

obtained during testing at the reference and applicant’s facilities. Correlation factors are usually applied 

to corrected, not raw, data. For example, when a correlation factor is developed for a choked engine, the 

x-axis may represent corrected thrust, corrected rotor speed, or EPR, and the y-axis would be used for 

plotting the appropriate correlation factor. 

(d) When using a one-away facility for reference testing, caution should be used in 

determining correlation factors for the applicant’s facility. The one-away facility may not have exactly

repeated the OEM’s baseline facility performance curve characteristics. As long as the one-away’s 

characteristics were within the manufacturer’s acceptable run-to-run tolerance, then a correlation factor 

applied to the one-away facility would not have been necessary. When a third facility’s (or applicant’s) 

characteristics are compared to the one-away’s performance characteristics and found to be within the 

same manufacturer’s acceptable run-to-run tolerance, there exists a potential for compounding the 

acceptable tolerance. This results in an error greater than the allowed tolerance relative to the baseline 

facility. The potential compounded tolerance error can be averted by taking into account the 

characteristic differences between the one-away and baseline facilities when evaluating the correlation 

factor for the applicant’s facility. The possibility of compounding tolerance errors becomes greater the 

further the reference facility is from the baseline facility, with respect to correlation. Paragraph 400a 

provides additional information on this. 

NOTE: As previously discussed, every effort must be made to completely eliminate 

or compensate for all measurement errors during data analysis. Once this is 

accomplished, attributing the remaining known minor, but elusive, differences to 

the correlation factor is generally acceptable. For example, there might be a 

5-degree measured and corrected EGT difference between the applicant’s facility 

and the reference facility. The applicant’s facility would then apply the 5 degree 

difference to all future measured and corrected EGT data. This methodology 

should be applied only when the parameter has a constant error over the entire 

engine operating range and is constant from test to test. 

NOTE: If the characteristic curve shapes for a particular parameter measured at 

the two facilities are divergent (not parallel), then this error should not be applied as 

a correlation factor. The error would result in the cell producing erroneously 

variable data during future acceptance testing of engines at the applicant’s facility. 

In this case, a continued effort should be made to determine the cause and eliminate 

the error.

Page 28 Par 401 
12/26/02 AC 43-207 

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: 

The test cell geometry, preferably including sketches and engineering drawings

Correlation engine configuration, including its serial number and the bellmouth, fan exhaust 

nozzle, and primary exhaust nozzle areas 

A listing of dress kit part numbers and serial numbers where possible 

Results of the fuel sample analyses

Significant changes made to the test cell, dress kit, and engine since the last correlation 

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 
AC 43-207 12/26/02 

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 
12/26/02 AC 43-207 

(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: 

Engine test hardware (e.g., dress kit) 

Facility inlet and exhaust 

Data acquisition: manual to automated acquisition, manual to automated reduction 

(calculation), and scanning, averaging, and editing

Instrumentation: type, quantity, and location 

Thrust stand 

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 
AC 43-207 12/26/02 

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: 

Instrument calibration 

Inspection or checks of measurement systems 

Inspection and repair of intake and exhaust systems (e.g., splitter panels, augmentor tube) 

Lubrication of moving parts 

Activation of valves and limit switches 

Inspection and repair of cell structural surfaces 

Intake screen debris removal 

Exhaust cleaning

Engine intake and exhaust nozzle inspections 

Oil system flushing

Emergency system testing 

Personnel training

NOTE: These practices can be characterized as good housekeeping and preventive 

maintenance. 

Page 32 Par 403 
12/26/02 AC 43-207 

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 

12/26/02 AC 43-207 

 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. 

 Page 1 
AC 43-207 12/26/02 

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. 

Page 2 
12/26/02 AC 43-207 

 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) 

12/26/02 AC 43-207 

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)

C

O

R

R

E

CTED EGT (

DEG

R

EES FA

H

REN

H

EIT)

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) 

12/26/02 AC 43-207 

Appendix 4

APPENDIX 4. GLOSSARY OF ACRONYMS AND ABBREVIATIONS

AC advisory circular 

ACO Aircraft Certification Office

ARP Aerospace Recommended Practice 

ASTM American Society for Testing and Materials 

DER Designated Engineering Representative 

EGT Exhaust Gas Temperature 

EPR Engine Pressure Ratio 

F Temperature in degrees Fahrenheit 

FAA Federal Aviation Administration 

fps feet per second 

FSDO Flight Standards District Office 

in-HgA Inches of Mercury Absolute 

ISO International Standards Organization 

K Temperature in degrees Kelvin 

kPa kilopascal absolute 

LHV Lower Heating Value 

NIST National Institute of Standards and Technology

OEM Original Engine Manufacturer 

Pcd Cell Depression 

psi Pounds Per Square Inch 

psia Pounds Per Square Inch Absolute 

QEC Quick Engine Change

R Temperature in degrees Rankine 

SAE Society of Automotive Engineers 

Page 1 (and 2)