Part of GE’s Aviat ion Business

 SERVICE BULLETIN .

SERVICE BULLETIN

SERVICE BULLETIN 61-A1125

TRANSMITTAL LETTER FOR REVISION NO.2

Aug 25/10

1. REASON

A. Service Bulletin compliance changed to ALERT.

B. To advise operators that the requirement for the continued inspection of hub assemblies 

Part No. 660709201can be terminated by the introduction of a revised hub assembly in accordance with 

Dowty Propellers Service Bulletin 61-1143.

C. Service bulletin reformatted.

2. ACTION

A. Remove and destroy existing pages 1 to 3 of the service bulletin and replace with revised pages 1 to 3 

dated Aug 25/10.

B. Remove and destroy existing pages 1 to 6 of Appendix A and replace with revised pages 1 to 6 dated 

Aug 25/10.

C. Remove and destroy existing pages 1 of Appendix B and replace with revised pages 1 dated Aug 25/10.

D. Remove and destroy existing pages 1 to 13 of Appendix C and replace with revised pages 1 to 13 dated 

Aug 25/10.

E. Remove and destroy existing pages 1 to 7 of Appendix D and replace with revised pages 1 to 7 dated 

Aug 25/10.

Dowty Propellers

Anson Business Park, Cheltenham Road East, Gloucester, GL2 9QN ENGLAND

Telephone: 01452 716000 Facsimile: 01452 716001

Page 1 of 3

ALERT

CAGE CODE: U7387

For Europe, Africa, India and

Middle East contact:

Dowty Propellers

Anson Business Park

Cheltenham Road East,

Gloucester, GL2 9QN, United Kingdom

T: + 44 (0)1452 716000

F: + 44 (0)1452 716001

For Asia, Australasia and the Pacific

contact:

Dowty Propellers

Anson Business Park

Cheltenham Road East,

Gloucester, GL2 9QN, United Kingdom

T: + 44 (0)1452 716000

F: + 44 (0)1452 716001

For the Americas

contact:

Dowty Propellers

114 Powers Court

Sterling, VA 20166

United States of America

T: + 1 (703) 421 4434

F: + 1 (703) 450 0087

Copyright (2010), GE Aviation Systems Ltd., U.K

The information contained in this document is GE Aviation Systems Ltd proprietary information and is disclosed in confidence. It is the

property of GE Aviation Systems Ltd and shall not be used, disclosed to others or reproduced without the express written consent of GE

Aviation Systems Ltd, including, but without limitation, it is not to be used in the creation, manufacture, development, or derivation of any

repairs, modifications, spare parts, designs, or configuration changes or to obtain FAA, CAA, EASA, or any other government or 

regulatory approval to do so. If consent is given for reproduction in whole or in part, this notice and the notice set forth on each page of

this document shall appear in any such reproduction in whole or in part.

All technical documentation and information contained herein, with respect to assembly and disassembly, cleaning, inspection methods

and limits, repair methods and limits, operational limits, life limits and the like, have been developed and approved for use with this

equipment and parts that have been manufactured and/or approved by GE and that have been maintained in accordance with GE 

technical documentation and recommendations. GE has no contractual or legal obligation for, nor knowlege of, non-GE-approved parts

and repairs. Accordingly, this document is not intended to apply to non-GE-approved parts and repairs.

Manual Ref: 61-10-20

SERVICE BULLETIN

PROPELLER - HUB WALL CRACKING

1. Planning Information

WARNING: FAILURE TO IMPLEMENT ANY INSTRUCTION GIVEN HERE, AS AMENDED FROM TIME TO

TIME BY DOWTY PROPELLERS, MAY ENDANGER HEALTH AND SAFETY.

A.

B. Effectivity

Aircraft affected : Merlin IVC/Metro III

Unit affected : Propeller

Part/Type No. : All R321/4-82-F/8 propellers

C. Reason

(1) On a similar propeller type, there have been reports of cracks originating from around the threaded

insert holes of the rear half hub which in one instance has resulted in a complete propeller

separation from the engine flange.

(2) To inspect for cracks in the rear wall of propeller hub assemblies Part No. 660709201.

D. Description

(1) Hub assemblies Part No. 660709201 are to be inspected in accordance with Appendix A or

Appendix D of this bulletin.

Non. Mod.

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ALERT

E. Compliance: ALERT

(1) Hub assemblies Part No. 660709201 included in propellers installed on aircraft must:

- have a repetitive inspection at an interval of not more than 1000 flying hours.

(2) Hub assemblies Part No. 660709201 included in propellers in storage must:

- have a repetitive inspection at an interval of not more than 1000 flying hours after the

installation of the propeller to an aircraft.

(3) Hub assemblies Part No. 660709201 in storage must:

- have a repetitive inspection at an interval of not more than 1000 flying hours after the

installation of the hub assembly onto an aircraft.

(4) The requirement for the continued inspection of hub assemblies Part No. 660709201 can be

terminated by the introduction of a revised hub assembly in accordance with Dowty Propellers

Service Bulletin 61-1143.

F. Approval

(1) This service bulletin was approved and classified as MANDATORY by the United Kingdom Civil

Aviation Authority. The technical content of this bulletin which affects airworthiness was approved

by a representative of the United Kingdom Civil Aviation Authority dated Apr 30/02.

G. Manpower

(1) Normal time for propeller removal and installation plus approximately 0.5 manhour to carry out the

NDT inspections. 

NOTE : The above manhours are given for shop planning purposes only. Dowty Propellers will not

be responsible for the cost of these manhours. The estimate assumes that the equipment

has been placed in a maintenance status and does not include preparation or

administrative functions.

H. Material

(1) None.

I. Tooling

(1) Equipment and materials as listed in Appendix A or Appendix D of this bulletin. Equipment in

Appendix A, para 2.B. and 2.C. and Appendix D, para 2.B. is available from Dowty Propellers on

request.

J. Weight and Balance

(1) None.

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ALERT

K. References

(1) Aircraft Maintenance Manual.

(2) Dowty Propellers Aircraft Maintenance Manual Pub. No. 1009.

(3) Dowty Propellers Component Maintenance Manual 61-10-20.

(4) Appendices A, B, C and D of this bulletin.

L. Other Publications Affected

(1) None.

2. Material Information

A. None.

3. Accomplishment Instructions

A. Embodiment Instructions

(1) Inspect the propeller hub rear half rear wall to the instructions at Appendix A or Appendix D of this

bulletin. Record all data from the inspections carried out on Appendix B and forward all reports to

Dowty Propellers as per para 3. B. (1). Defective hubs, if any, are to be returned to Dowty

Propellers for further investigation.

B. Reporting Instructions

(1) Reports of all inspections are to be forwarded by FAX to the Technical Support Manager, Dowty

Propellers, Fax. No. 44 1452 716001. The following information is required. 

(a) Hub serial number.

(b) Hub total flying time since new.

(c) Hub flying time since overhaul.

(d) Hub crack details if found, or report ‘Satisfactory’ if uncracked.

(e) Confirmation of use of NDT methods specified in this service bulletin.

(f) A photocopy of the hub log cards.

C. Recording Instructions

(1) Record the compliance with the instructions of this service bulletin in the propeller log book.

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APPENDIX A

THE ULTRASONIC INSPECTION OF THE MERLIN/METRO PROPELLER HUB (REAR HALF)

1. Introduction

A. This technique is designed for the detection of fatigue cracking originating from and around the threaded

insert holes. (Figure 1).

B. This technique will necessitate removal of the propeller. It is not necessary to remove the backplate.

C. The scan area as shown in Figure 1 must be clean and free from surface damage.

2. Equipment Required

A. Ultrasonic flaw detector operating in the 1 to 15 Mhz range. (A Sonatest Masterscan 335 was used in the

preparation of this technique, operating at 15 Mhz).

B. A 3 mm (0.125 in) diameter 5Mhz longitudinal probe type No. Panametrics V1091 or equivalent.

C. Reference block Part No. DAPT 09-0001-00 detail 9 (Apply to Dowty Propellers for a manufacturing

drawing. Appendix C includes NDT 5DAP which is required for the manufacture of the reference block).

D. Suitable couplant.

3. Calibration Procedure.

A. Using a suitable couplant, place the probe on the reference block.

B. Using standard calibration procedure establish the probe zero position.

C. By probe movement identify the signal from the flat bottom hole and set at 6.0 on the timebase. (See

Figure 3).

D. Maximise this signal and set amplitude to 80% full screen height. (See Figure 3).

4. Inspection Procedure

A. Apply couplant to hub mounting face in scan area and position probe as shown in Figure 1.

B. A back wall echo will appear at approx. 6.0 on the timebase. (See Figure 4). This signal will vary in

amplitude from 5 - 100% full screen height due to the inside face geometry.

C. Scan 360_ of scan area.

D. Discontinuity indications may appear at any position along the timebase, between 1.0 and the back wall

echo signals. They may appear as a single indication or a multiple peak indication as shown in Figure 5.

5. Inspection Standard

A. Any indication which, after careful cross-checking of calibration procedure, is 20% of full screen height or

more is to be considered as a defect and rejected.

NOTE : Indications from the thread flanks may appear up to 15% full screen height. (See Figure 4).

B. Mark up a ’Status Report’ reproduced from Appendix B of this service bulletin. Supply all the information

required in lines 1 to 9. Record all data from the inspection and FAX to the Product Support Manager,

Dowty Propellers, Fax. No. 44 1452 716001.

C. Rejected hubs are to be returned to Dowty Propellers for further investigation.

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Scan Areas A

Figure 1

61-10-27

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Possible Crack Orientation

Figure 2

61-10-27-1

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Signal From Reference Block

Figure 3

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Back Wall Echo And Thread Signal

Figure 4

Appendix A

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Typical Crack Signal

Figure 5

Appendix A

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APPENDIX B

STATUS REPORT

THE ULTRASONIC INSPECTION OF THE MERLIN/METRO PROPELLER HUB (REAR HALF)

1. Operator .............................................................

2. Aircraft Serial No. ..............................................

3. Propeller Installation (delete whichever is not applicable)

4. Propeller Serial No. .........................................

5. Hub Serial No. ..................................................

6. Hub total flying hours since new ..................... Flying Hours

7. Hub total flying hours since overhaul ..................... Flying Hours

8. Crack indications and details if any (illustrate above) ...........................................................................................

..............................................................................................................................................................................

Report ‘Satisfactory if no cracks are found.

9. Inspectors stamp or signature ..............................................................................................................................

61-10-27-2

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Appendix B

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APPENDIX C

NDT 5DAP

ULTRASONIC FLAW DETECTION

1. Scope.

A. NDT 5DAP supersedes NDT 5 for all future Dowty Aerospace Propellers contracts. Where existing

drawings/documents call up NDT 5, NDT 5DAP must be used in lieu.

B. This specification explains the control and calibration requirements for all ultrasonic inspection equipment

(sets, probes and reference blocks) at DAP. Sub-contracting agencies must also meet the requirements

described here-in when inspecting components for DAP. Wherever possible National or International

standards have been referenced, this is planned to reduce the need for frequent re-issues, and make this

specification easier to adhere to.

C. Individual inspection procedures are issued at DAP as separate documents. E.g. for Immersion

longitudinal or Contact etc. In addition to these procedures an individual technique must be raised to each

component or part number. These procedures and techniques must be approved by an appropriate level

III NDT engineer, and, technique numbers must be referenced on the relative drawing or layout. Subcontracting agencies must maintain Procedures and techniques relevant to their own equipment.

D. The requirements to carry out ultrasonic flaw detection on raw materials are given in BS L100 and 

BS S100 such ultrasonic inspection is normally the responsibility of the supplier. When carried out at DAP,

the methods and standards referred to in the British Standards shall be applied. Sample inspection may

be applied in this case.

E. Where parts are manufactured by DAP on a sub-contract basis, the ultrasonic inspection requirements of

the main contractor will apply unless agreement has been reached to apply this specification.

F. Repair and overhaul ultrasonic inspection of parts for the purpose of detection of in-service defects, is

covered by techniques associated with service bulletins or Ministry of Defence instructions, usually

servicing instructions (SI’s) or special technical instructions (STI’s).

These techniques are usually derived from product support techniques prepared by DAP NDT technicians.

NOTE : Where deemed necessary DAP may use the product support technique system for cases not

covered by paragraph F.

When the repair or overhaul of a part uses methods or processes used on production to which

ultrasonic inspection would apply, the same inspection technique shall be applied to the repair of

the used part.

2. Personnel Requirements.

A. Personnel operating this inspection procedure at DAP must be qualified in accordance with the

requirements of NDT 10DAP. Sub-contracting agencies must maintain their own personnel certification

scheme, this in turn, must be approved by DAP.

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3. References

A. BS L100 Inspection & testing of wrought aluminium and aluminium alloys.

B. BS S100 Inspection & testing of wrought steel.

C. ASTM E 114 Practice for ultrasonic pulse-echo straight beam testing by the contract method.

D. ASTM E 127 Practice for fabricating and checking aluminium alloy ultrasonic standard reference

blocks.

E. ASTM E 214 Practice for immersed ultrasonic examination by the reflection method using pulsed

longitudinal waves.

F. ASTM E 317 Practice for evaluating performance characteristics of pulse-echo testing systems

without the use of electronic measurement instruments.

G. NDT 10DAP Approval of personnel for NDT Inspection.

4. Procedure and Techniques

A. The procedures in use at DAP are separate documents to this specification. In addition to the procedures,

an individual technique for each component or part number is required. (See paragraph 1.C.). As a

minimum each technique shall include the following:-

(1) Company Name

(2) Technique Number

(3) Related Inspection Procedure

(4) Acceptance Class (Refer to international/national standards or drawing requirements)

(5) Inspection Scan Cover

(6) Part No. & Material

(7) Manufacturing Stage

(8) Transducer Type Diameter & Frequency

(9) Couplant

(10) Transfer Method (If Used)

(11) Reference Standards

Appendix C

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5. Equipment Calibration Requirements.

A. Electronic Flaw Detector Unit.

(1) Calibration Requirements:-

(a) Electronic Flaw Detector units which are to be used for immersion techniques are to be

calibrated annually in accordance with the procedure stated in paragraphs 5.A.(2) (a) to (e).

This is to be carried out by a level II or III approved NDT Technician and tagged with a

calibration label. All calibration graphs are to be kept on file in the calibration control area.

(b) Electronic Flaw Detector units which are to be used in the contact mode alone are to be

calibrated in accordance with the procedure stated in paragraphs 5.A (2) (a), (b) and (e).

This calibration is to be carried out be a level II or II approved NDT Technician on a6 monthly

basis and tagged with a calibration label. All calibration graphs are to be kept on file in the

calibration control area.

(2) Calibration Procedure

This procedure is based on the requirements and methods described in ASTM-E-317. If this

procedure is used for evaluating contact sets consistent and uniform coupling must be ensured.

When used for immersion equipment ensure the probe exit surface and test blocks are free form air

bubbles, always allow time for equipment to stabilise.

(a) Horizontal limit and linearity

Select an appropriate test block that when coupled to the search unit (either by contact or

immersion) will produce eleven back reflections on the flaw detector which is being checked.

Use the instrument gain, delay and calibration settings to set the leading edge of the third and

ninth back reflection at 20% and 80% scale division respectively (when reading reflection

positions always set at the amplitude of that reflection to 50% full screen height). Once the

third and ninth reflections are positioned at 20% and 80%, read and record the scale position

of each other multiple.

Interpretation of results:-

The horizontal limit is given by the maximum available trace length falling within the screen

graticule. This must, in all cases be 100%. Failure to obtain full scale deflection may indicate

an equipment malfunction. Horizontal linearity results are best plotted in graphical form as

shown in figure 3. The deviation is given by the displacement (in % of full scale) from the

straight line through the set up points, which represents ideal linearity. The maximum

displacement allowed is 5% of full scale.

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(b) Vertical limit and linearity

This check requires the use of a test block which, when coupled to a suitable search unit will

produce signals having an amplitude ratio of 2 to 1 on the flaw detector being examined.

(Signals do not have to be successive or in any particular order). Designate these signals HA

and HB (HA being larger) and ensure that there is sufficient range in the gain control to vary

HA from 10% fsh to 100% fsh. Set signal HA to 60% fsh, this should give a resultant HB

signal of 30% fsh (some deviation allowed see Table 1).

Once this is set adjust the gain control to increase HA up to 100 fsh in increments of 10% or

less. At each step read and record the amplitude of HA and corresponding amplitude HB.

Return gain setting to original position and check that HA and HB are also at original levels.

Now, reduce gain to bring HA to 10% fsh in increments of 10% or less, read and record HA/HB

values at each increment.

Interpretation of results:-

Vertical limit is given by the maximum vertical deflection within the graticule range that can be

obtained from a large reflector. This figure must in all cases be 100% of full scale deflection

failure to obtain full scale deflection may indicate an equipment malfunction.

Vertical linearity results are best displayed graphically as shown in figure 3. Ideal linearity is

indicated by a line from the origin through the set up point (HA60, HB30) to full scale.

Actual linearity must be within ± 5% of ideal linearity.

(c) Resolution

Any method for determination of equipment resolution may be used, if authorised by an

approved level III NDT Engineer. This section describes one method, it is an overall system

check, therefore it may be used for both search units and flaw detector sets.

This check requires the use of test block number DAPT 09-0045-00. The block incorporates

both front and back surface flat bottom hole references of 2/64, 3/64 and 5/64ths′′ diameter,

each at distances of 0.060′′, 0.125′′ and 0.250′′ from the respective front or back surface (see

drawing DAPT 09-0045-00).

First, couple the search unit to the near surface check area of the block, and determine by

careful probe movement the smallest hole diameter detectable and the shortest metal trace

distance it can be resolved from the entry surface indication.

A hole is said to be resolved when a signal of 80% fsh can be established from that hole; it is

clearly separated from the adjacent interface indication down to at least 20% fsh, and there

are no residual indications over 20% fsh throughout the test region.

Next move the probe to the back surface check section of the block and repeat process, this

time establish the smallest hole size resolvable, at the shortest metal travel distance from the

back wall echo.

Interpretation of results:-

Record the smallest resolvable hole diameter, at the shortest metal path distance from front

and back surfaces on the relevant test certificate. This information may then be used to

verify the suitability of equipment for a certain task.

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(d) Sensitivity and Noise

This check requires the use of ASTM-E-127 light alloy reference standards, various blocks

are suggested for various search unit frequencies:-

Test Frequency 0.4-1.5Mhz 1.0-2.5Mhz 2.0-10Mhz

5.0300 to 2.0300 to 1.0300 to

8.0300 6.0300 5.0300

With the instrument sensitivity at maximum, determine the smallest hole size that will give an

indication having an amplitude of at least 60% fsh and baseline noise of no more than 20%

fsh in the test region. If the dimensions of the test block allow move the search unit just away

from the hole and determine that noise at maximum sensitivity exceeds 20% fsh, reduce the

gain until 20% fsh is obtained and determine the smallest hole that will then produce a 60%

fsh or greater indication. Record the block number, noise level, signal amplitude and reduced

gain. If the indication from the smallest hole available exceeds 100% fsh use the gain control

to lower the hole indication to 60% fsh, and record the remaining available gain that does not

cause the noise to exceed 20% fsh.

Interpretation of results:-

Record all the information derived i.e. Block No. noise level, signal amplitude, reduced gain (if

applicable) and gain in hand (if applicable) on the appropriate calibration certificate. This

information may then be used to verify the suitability of equipment for a certain task.

(e) Linearity of equipment gain

This check relies upon the vertical linearity of the flaw detector previously being established

as acceptable [see paragraph 5.A.(2) (b)].

Using test block ASTM-E-127 5-0300 establish by probe manipulation and flaw detector

adjustments, an 80% fsh indication from the flat bottomed hole. Note the gain setting and

designate this XdB. Next, ensuring constant probe coupling and no other flaw detector

alterations adjust the gain settings by the dB amounts shown in Table 2, and record the

resultant % fsh indications from the flat bottomed hole.

Interpretation of results.

All the indications must lie between the maximum and minimum limits as designated in Table

2.

B. Calibration and Control of Transducers. (Probes).

This section covers calibration of contact probes (both compressional and shear wave) and immersion

probes (focused and unfocused). All immersion probes must be calibrated annually, the calibration

certificate kept on file and the probe tagged with a calibration due date. For all probe calibrations use a

flaw detector calibrated to paragraph 5.A.

(1) Contact Transducers

Providing a contact transducer meets the set-up and calibration requirements of a specific

technique it can be used for that technique, therefore there would be no requirement to assess the

transducer for parameters such as dead zone, beam profile, resolution, sensitivity etc.

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(2) Calibration of Unfocused immersion transducers

(a) This procedure is to be carried out on all unfocused water immersion probes.

(b) Equipment

1 An immersion tank of suitable size with an adjustable probe manipulator is to be used.

2 A 12,5 mm diameter ball is to be used as the target.

3 An instrument, capable of measurement of 0,025 mm or better is to be used to measure

beam width.

(c) Procedure

NOTE : For the Beam Axis alignment procedure which follows, use the bracketed alternative

position when NF is less than 150 mm.

1 Carry out the following calculations.

a Calculate the theoretical Near Field (NF) distance for the probe:

NF=(D x F) where D = Probe diameter

 8c F = Frequency of probe

c = Speed of sound in immersion 

 fluid water = 1483 m/s at 20°C

b Calculate the 2/3 rds NF distance

c Where NF is 150 mm or greater, calculate the 5/6th NF distance.

2 Mount the ball at least 75 mm below water level.

3 Position the probe against the ball and adjust such that the crystal is concentric with the

ball.

4 Move the probe back to the 2/3 rds NF position. Using Tilt and Vertical adjustment,

obtain the maximum amplitude signal, ensuring the crystal remains concentric with the

ball.

5 At the 2/3 rds NF distance, obtain maximum amplitude signal using the Swing and

Lateral adjustments.

6 At the 5/6 ths NF distance check that no increase in amplitude can be obtained by

Vertical or Lateral adjustment.

7 Carry out the same check at full NF distance. Adjustments must be made such that

maximum amplitude signal can be obtained at the three positions without alteration of

adjustments. This ensures that the ball remains on Beam Axis with probe movement.

8 Move the probe over the theoretical NF distance. A maximum amplitude signal should

be obtained in the middle region. Adjust its amplitude to just below full screen height, or

to the upper linear limit.

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9 Position the probe 5 mm from the ball and record the amplitude of the signal. Repeat at

5 mm increments over the 2/3 rd NF range. Continue at 10 mm increments until the

signal has reduced at approximately 1/5 th screen height.

NOTE : The following procedure of adjustment will eliminate errors due to backlash in

the lateral movement.

10 Beam width is now measured, starting at this final probe position. Adjust the signal

amplitude to 80% screen height. Using lateral adjustment, move the probe until the

signal reduces to below 40% of screen height. Carefully adjust in the opposite direction

until the signal is 40% screen height (6dB down). Using the measuring instrument,

measure and record the position of the carriage. Continue the lateral movement of the

carriage such that the signal increases, then decreases to the 40% height. Care must

be taken not to overshoot this position. Measure and record the carriage position.

Deduct the smaller from the larger reading to obtain beam width.

11 Repeat this beam width measurement procedure at the 5/6 th and 2/3 rd position.

12 Beam width measurements are to be taken at gradually reduced increments as the

probe is advanced closer to the ball. Prior to each position measurements at less than

2/3 rds NF, the probe is to be returned to beyond the 2/3 rds position and maximum

height signal obtained on the lateral movement.

13 Using figure 1 ‘Probe Calibration’ sheet, record details and readings, and plot the

Distance/Amplitude Curve and Beam Width.

(d) Assessment of Results

1 A good result has been achieved when beam width is wide when amplitude is low, and

narrow when amplitude is high. The result must satisfy this before acceptance.

2 Mark on the curve the near and far positions where the signal amplitude falls to 50% of

maximum. From this, the following Optimum Operational Data is to be entered on the

sheet.

a Water Gap Distance to the ’near’ mark

b Working Range Distance between the two marks in water (Divide by 4 for

steel or aluminium)

c Scan Index Beam width at ’near’ mark. This should be in excess of 3mm

for standard search probes.

(3) Calibration of focused immersion transducers

(a) This procedure is to be carried out on all focused water immersion probes.

(b) Equipment

1 An immersion tank of suitable size, is to be used.

2 A 12.5 mm diameter steel ball is to be used as the target.

3 An instrument capable of measurement of 0,025 mm or better is to be used to make

beam profile measurements.

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(c) Procedure

1 Obtain the manufacturer’s nominal focal distance for the probe.

2 Mount the ball at least 75 mm below water level.

3 Position the probe against the ball and adjust such that the crystal is concentric with the

ball.

4 Move the probe back to the nominal focal distance. Using Tilt and Vertical adjustment,

obtain the maximum amplitude signal, ensuring the crystal remains concentric to the

ball.

5 Still at the nominal focal distance, obtain the maximum amplitude signal using the Swing

and Lateral adjustments.

6 Increase the distance of the probe to the ball by 20 mm. Check for increase in amplitude

by Vertical and Lateral adjustment. Carry out adjustments until maximum signal is

obtained at nominal focal distance and at this position + 20 mm without any further

adjustment being necessary. This ensures that the ball remains on Beam Axis with

probe movement. It may be necessary to check this maximum at a third position.

7 Move the probe towards the ball until maximum signal is obtained. Adjust signal to

upper Linearity limit for the equipment. Re-check concentricity of probe and ball.

8 Position the probe 5 mm from the ball and record the amplitude of the signal. Repeat at

5 mm intervals (or less where necessary) over the nominal focal distance. Continue at

10 mm intervals until the signal has reduced to approximately 1/10 th screen height.

9 Beam width measurement is now carried out in the same way as outlines in para 10 of

Part 2(c). Measurements are taken at 5 mm intervals from the ball to at least 20 mm

past the maximum height position. Thereafter at 10 mm intervals over the remainder of

the Distance Amplitude plot.

10 Record all details and construct graphs of Distance/ Amplitude and Beam Width on the

left half of figure 2.

11 Beam Profile measurements are now carried out at the actual maximum amplitude

distance from the ball and at approximately 1.3 times this distance, e.g.: If actual max.

amplitude distance is 30 mm., the second position could be taken as 40 mm.

12 At the 1.3 times max. position, set the signal amplitude to the upper linearity limit. Using

the lateral adjustment on the rig, move the probe in increments of 0,25 mm one

direction, recording amplitude, until below 5% fsh. Repeat in the opposite direction.

13 This is repeated at the maximum amplitude position in two planes at 90° (i.e. rotate

probe in holder for second run). The probe is to be moved at least 5 mm each side of

centre line and any side lobes are to be plotted.

14 Plot the results on the right hand half of figure 2.

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(d) Assessment of Results

1 Actual Focal Distance - This is the distance on the Distance/ Amplitude Curve at which

the amplitude is at maximum. This may differ considerably from the nominal figure given

by the manufacturer, but should be similar for probes of the same specification. Record

this distance in the Block on figure 2.

2 Focal Spot Size - This is to be measured at Actual Focal Distance and recorded in the

Block in figure 2.

3 Beam Profile - This is to be assessed for symmetry about the centreline and side lobe

conditions.

4 Symmetry:- The ratio of distance each side of centreline at which amplitude is 50% of

max. - should not exceed 1.5 to 1.

5 Side lobes:- Amplitude must not exceed 20% of maximum.

C. Calibration of Ultrasonic Reference Blocks

(1) General Requirements

(a) It is advisable to calibrate reference blocks by comparing them to other reference blocks of

known accuracy. In the case of Aluminium Alloy and Steel standard reference blocks, this

can be done by comparing them with blocks of known accuracy.

(b) Master Reference Blocks.

Master reference blocks shall be used only for calibrating other reference blocks of the same

part number. They shall not be used as a working block. Calibration is carried out at initial

issue, to the relevant drawing.

(c) Working Reference Blocks

Working reference blocks are to be calibrated on initial issue and 5 yearly thereafter.

Blocks that are to be used with contact techniques only may be calibrated by the contact

method using an instrument qualified to section 5A and a suitable transducer. When blocks

are to be used with immersion techniques an instrument, qualified to section 5A, is to be used

in conjunction with a 10 MHz, 10mm diameter standard water immersion probe, calibrated to

section 5C. The serial numbers of the instrument and Probe are to be entered on the

calibration certificate (DAP 614). When re-calibration is being carried out, the same

Instrument and Probe combination as originally employed should be used. If an alternative

probe is necessary, select one with calibration curve nearest to the original.

(d) When it is required to compare a flat bottomed hole of a different diameter to the master the

following factors are to be used.

1/64 to 2/64′′ = 12dB

2/64 to 3/64′′ = 7dB

3/64 to 5/64′′ = 9dB

5/64 to 6/64 = 8dB

(e) The amplitude of the signal form a block being calibrated must be within ± 3dB of the master

reference block. Blocks within tolerance are to have their error marked on them. When the

signal is less in amplitude than the master, the correction factor is to be marked positive, and

vice-versa.

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Table 1

Acceptable Initial Values for HA and HB

Table 2

SET-UP LIMITS

RATIO 2.2 2.0 1.8

HA HB MIN. HB NOM. HB MAX.

65

64

63

62

61

30

29

29

28

27

33

32

32

31

31

36

36

35

34

34

PREFERRED 60 27 30 33

59

58

57

56

55

27

26

26

25

25

30

29

29

28

28

33

32

32

31

31

Nominal HA values are preferred for any give HB value.

Gain Setting Expected % fsh

 Response

Maximum % Minimum %

X+2dB 100 100+ 90

XdB 80 - -

X-6dB 40 45 35

X-18dB 10 12 8

X-24dB 5 - Signal must be visible

 above base line 

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Figure 1

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Figure 2

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Figure 3

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APPENDIX D

NDT UT72

THE ULTRASONIC INSPECTION OF THE GENERAL AVIATION

3 & 4 METAL BLADED PROPELLER HUBs

1. Scope.

A. This technique details the contact pulse echo method of ultrasonic inspection for the detection of fatigue

cracking from the 8 threaded insert holes, on the rear half hub.

B. It will be necessary to remove the propeller from the engine drive flange remove the backplate and slip

ring.

C. The ultrasonic equipment is to be calibrated in accordance with NDT 5DAP.

D. Personnel carrying out this technique must be qualified to NDT 10DAP.

2. Equipment Required.

A. Ultrasonic flaw detector operating in the 1 to 15 Mhz range. (A Sonatest Masterscan 335 was used in the

preparation of this technique).

B. A 3 mm (0.125 in) diameter 5Mhz longitudinal probe type No. Panametrics V1091 or equivalent.

C. Suitable couplant.

3. Calibration Procedure.

A. Using a suitable couplant, place the probe on the hub adjacent to the dowel hole as shown in Figures 1

and 2.

B. Using standard calibration procedure establish the probe zero position.

C. By probe movement identify the signal from the dowel hole and set at 1.6 on the timebase. (SeeFigure 4).

D. Maximise this signal and set amplitude to 80% full screen height, (see Figure 4), then add 6dB.

4. Inspection Procedure.

A. Apply couplant to hub mounting face in scan area and position probe as shown in Figures 2 and 3.

B. A back wall echo will appear at approx. 6.0 on the timebase. (See Figure 5). This signal will vary in

amplitude from 5 - 100% full screen height due to the inside face geometry.

C. Scan 360° of scan area.

D. Discontinuity indications may appear at any position along the timebase, between 1.0 and the back wall

echo signals. They may appear as a single indication or a multiple peak indication as shown in Figure 6.

5. Inspection Standard.

A. Any indication which, after careful cross-checking of calibration procedure, is 20% of full screen height or

more is to be considered as a defect and rejected.

NOTE : Indications from the thread flanks may appear up to 15% full screen height. (See Figure 5).

B. Rejected hubs are to be returned to Dowty Propellers for further investigation.

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Probe Position for Calibration

Figure 1

UT 72 F1

PROBE POSITION FOR CALIBRATION

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Figure 2

UT 72 F2

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Typical Crack Orientation

Figure 3

UT 72 F3

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Signal From Hub Dowel Hole

Figure 4

Appendix D

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Signals From Back Wall Echo and Threads

Figure 5

Appendix D

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Typical Crack Signal

Figure 6

Appendix D

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