REASON 

MODEL 

402C 

414A 

SERIAL NUMBERS 

402C0001 thru 402C1020 

414A0001 thru 414A1212 

Cracks have been discovered on some engine beams. The cracks extend from behind the doubler 

located forward of the aft engine mount or aft of the forward engine mount. 

DESCRIPTION 

This service letter provides instructions to do a radiographic (x-ray) and eddy current inspection of the 

engine beams for the left and right engine nacelles. 

NOTE: This x-ray inspection will require a radiographer that is qualified and certified to Level 2 or 3 per 

the requirements of NAS41 0 or equivalent. 

NOTE: The eddy current technician must be qualified and certified to Level 2 or 3 per the requirements 

of NAS 410 or equivalent. 

COMPLIANCE 

MANDATORY. This service letter must be accomplished on engine beams (5654109-X) with 15,000 or 

more flight hours as listed in the table that follows, and then every 200 flight hours until all four engine 

beams (56541 09-X) are replaced. 

Airplane Flight Hours Flight Hours and Days to comply 

Over 30,000 25 flight hours or 30 days, whichever occurs first 

25,000-30,000 50 flight hours or 45 days, whichever occurs first 

20,000-24,999 75 flight hours or 60 days, whichever occurs first 

15,000-19,999 100 flight hours or 90 days, whichever occurs first 

NOTE: After the initial inspection, this service letter inspection must be completed every 200 flight 

hours until all four engine beams (56541 09-X) are replaced. 

March 20, 2015 

MEL-54-01 

Page 1 of 12 

Cessna Aircraft Company, Cessna Customer Service, P.O. Box 7706, Wichita , KS 67277, U.S.A. 1-316-517-5800 

This document contains technical data and is subject to U.S. export regulations. This information has been exported from the United States 

in accordance with export administration regulations. Diversion contrary to U.S. law is prohibited. ECCN: 9E991 

COPYRIGHT© 2015 
0.12 Stainless Steel Commercially Available To measure the penetrating 

Penetrameter power of the X-ray. 

Lead Exposure Commercially Available Protection from X-ray 

Screens Exposure. 

0.12" AI. Shim Block Fabricate Locally To shim the penetrameter. 

0.1 0" SS Shim Block Fabricate Locally To shim the penetrameter. 

Eddy current Nortec 500 Olympus Eddy Current Test system. 

instrument 48 Woerd Ave 

Waltham, MA 02453 

0.125 in. Diameter MP905-60FX- Olympus Probe for Eddy Current Test 

right angle probe 1-3M system. 

Stainless Steel VMSS3RS-1.0 VM Products To test the Eddy current 

Reference Standard 11208 62nd Ave. E. System Calibration. 

(Note) Puyallup, WA 98373 

NOTE: If an equivalent is used in place of the Stainless Steel Reference Standard, the equivalent 

standards must have a 0.020" deep surface EDM notch. If a stainless steel reference standard is 

not available, a 6AL4V titanium reference standard may be used. 

REFERENCES 

Cessna Model 402C Maintenance Manual 

Cessna Model 414 Maintenance Manual 

PUBLICATIONS AFFECTED 

None 

ACCOMPLISHMENT INSTRUCTIONS 

1. Prepare the airplane for maintenance. 

A. Make sure that the airplane is electrically grounded. 

B. Make sure that all switches are in the OFF/NORM position. 

C. Disconnect electrical power from the airplane. 

(1) Disconnect the airplane battery. (2) Disconnect external electrical power. 

D. Attach maintenance warning tags to the battery and external power receptacle that have "DO NOT 

CONNECT ELECTRICAL POWER - MAINTENANCE IN PROGRESS" written on them. 

2. Open the cowl doors for each engine nacelle. (Refer to the appropriate sections in the Model 402C 

and 414 Maintenance Manual.) 

3. Remove the upper cowling from each engine nacelle. (Refer to the appropriate sections in the Model 

402C and 414 Maintenance Manual.) 

4. Disconnect or remove components as required to gain access to the engine beam. 

A. Secure disconnected or removed components so they do not interfere with the inspection. 

MEL-54-01 

Page 2 March 20, 2015 
NOTE: The steps that follow are required for each engine beam. Each engine beam will have two X

Ray 

images. One image will be forward of the aft engine mount and the second image will be aft of the 

aft engine mount. There will be a total of eight X-Ray images. 

NOTE: The radiographer must be qualified and certified to Level 2 or 3 per the requirements of NAS41 0 

or equivalent. 

A. (Refer to Table 1.) Place identification tape to the cassette. 

B. (Refer to Figure 1.) Place 0.12 inch stainless steel penetrameter on engine beam just forward or 

aft of the angle as shown. 

(1) (For the location forward of the aft engine mount.) Place shim blocks of 0.12 inch aluminum 

and 0.10 inch of stainless steel on top of penetrameter. 

(2) (For the location aft of the aft engine mount.) Place a shim block of 0.10 inch of stainless 

steel on top of penetrameter. 

C. (Refer to Figure 1.) Position the 5x7 film cassette on top of the engine beam and against the forward 

or aft side of the aft engine mount. 

D. (Refer to Figure 1.) Locate the x-ray tube as follows: 

24 inches below the engine beam. 

Primary x-ray beam to be perpendicular to the upper surface of the engine beam. 

The focal point is in the middle of the engine beam centerline and centered on the last row 

of fasteners that attach the upper angle to the beam (approximately 2 inches forward or aft 

of the aft engine mount). 

WARNING: WARNING: X-RADIATION PRESENTS A HAZARD TO HUMANS. 

FOLLOW ALL APPLICABLE FEDERAL, STATE AND LOCAL 

REGULATIONS FOR SAFE OPERATIONS OF X-RAY PRODUCING 

EQUIPMENT. 

E. (Refer to Table 1.) Expose film per Table 1 requirements. 

NOTE: Film density in the area of interest must be 1.8 to 3.5 H&D. Satisfactory sensitivity will be 

indicated by the penetrameters 2-2T hole. 

March 20, 2015 

MEL-54-01 

Page 3 
0.010B 

1A LH OB 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

2F LH INBD 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

2A LH INBD 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

3F RH INBD 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

3A RH INBD 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

4F RH OB 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

4A RH OB 5x7 0.005F/ 0.3 inch 24 inch 115 300 

0.010B 

NOTE: 1. Kodak M film was used to test this technique. Equivalent films may be used. 

NOTE: 2. 1.5 mm2 focal spot constant potential x-ray tube. Larger focal spot x-ray tube is 

acceptable if the 2-2T penetrameter sensitivity is attained. 

7. Do an examination of all the films looking for transverse cracks to the long axis of the engine. 

NOTE: If an obvious crack is not visible, use 7x to 1 Ox magnification as necessary. 

A. (Refer to the attachment) Add notes of any findings to the INSPECTION RESULTS FORM. 

B. If a crack is found. Contact Cessna Structures at: csstructures@txtav.com, or phone: 316-517-6061 . 

8. (Refer to Figure 3.) Calibrate the Eddy current probe. 

NOTE: The eddy current technician must be qualified and certified to Level 2 or 3 per the requirements 

of NAS 41 0 or equivalent 

A. Connect the probe to the eddy current instrument 

B. Set the eddy current instrument frequency to 2.0 MHz. 

C. Place the probe on the standard away from the EDM notches. 

D. Push the null (balance) button. 

E. Place the null point in the lower right quadrant of the instrument display at approximately the 70% 

horizontal and 20% vertical screen position. 

F. Adjust the phase angle to place the signal from lift-off traveling horizontal and to the left of the 

null point 

G. Adjust the instrument parameters to achieve a minimum vertical separation of 3 major screen 

divisions in signal amplitude between the null point and the 0.020 inch surface notch on the standard. 

MEL-54-01 

Page4 

NOTE: This is the scan reference or sensitivity level, this is not a reject level. There are no 

acceptable cracks. All relevant crack indications are suspect and shall be rejected 

regardless of the signal response amplitude. 

March 20, 2015 
A. Insert the eddy current probe into the lightning hole. 

CAUTION: There is a tooling hole on the forward side of the forward nut plate. The 

proximity of the hole to the nut plate may be close enough to influence the 

eddy current probe. 

B. Scan around each of the nut plate assemblies (2 each per beam) common to the forward engine 

mount installation. 

C. If the tooling hole influences the inspection, carefully scan up to the tooling hole from both directions 

and monitor the instrument display. 

D. If you are unsure if you have an indication from the tooling hole or a crack use a visual aide such as 

a video-probe to inspect the area adjacent to the hole. 

E. If a crack is found. Contact Cessna Structures at: csstructures@txtav.com, or phone: 316-517-6061 . 

F. (Refer to the attachment) Add notes of any findings to the INSPECTION RESULTS FORM. 

10. Do a detailed visual inspection of the external surfaces of each engine beam for cracks, corrosion and 

loose fasteners. Use a flashlight and a mirror or a flexible baroscope as necessary to complete a detailed 

visual inspection. 

NOTE: A detailed visual inspection is described as an intensive visual examination of a specific structural 

area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting 

is normally supplemented with a direct source of good lighting at an intensity deemed appropriate by the inspector. Inspection aids such as mirrors, magnifying lenses, etc. may be used. Surface 

cleaning and elaborate access procedures may be necessary 

A. If a crack or severe corrosion is found. Contact Cessna Structures at: csstructures@txtav.com, or 

phone: 316-517-6061 . 

B. (Refer to the attachment) Add notes of any findings to the INSPECTION RESULTS FORM. 

11. (Refer to the attachment) Complete the INSPECTION RESULTS FORM and return to Cessna at 

csstructures@txtav. com. 

12. Install any components that were removed to gain access to the engine beam in Step 4. 13. Install the upper engine cowling for each nacelle. 14. Close the cowl doors for each engine nacelle. 15. Remove the maintenance warning tags and connect the airplane battery. 

16. Send the INSPECTION RESULTS FORM to csstructures@txtav.com. 

17. Make an entry in the airplane logbook that states compliance and method of compliance with this service 

letter. 

March 20, 2015 

MEL-54-01 

Page 5 
MEL-54-01 

Page 6 

X-Ray Film 

(Forward) 

DETAIL A 

VIEW A-A 

Figure 1. Engine Beam X-Ray, Aft Engine Mount (Sheet 1) 

X-Ray Film 

(Aft) 

5210T1014 

March 20, 2015 
X-Ray Film 

(Forward) 

Aft Engine Mount 

(Reference) X-Ray Film 

(Aft) 

c 

i- + + + 

+ + iO+ + + + 

X-Ray Source 

(Forward) VIEW 8-8 

Penetrameter and 

Shims 

(Forward) 

X-Ray Film 

Position 

(Forward) 

Focal Point 

(Forward) 

Last Fastener Row On 

Angle As Shown 

VIEW C-C 

(Typical, All Locations) 

0-___ 

Penetrameter and 

Shim 

(Aft) 

c 

X-Ray Source Position 

(Aft) 

Penetrameter and 

Shim 

(Aft) 

X-Ray Film 

Position 

(Aft) 

Figure 1. Engine Beam X-Ray, Aft Engine Mount (Sheet 2) 

March 20, 2015 

MEL-54-01 

Page 7 
241nches 

Angles Installed By 

SK414-17 

X-Ray Film 

(Reference) 

J ..--- Engine Beam 

___.-- (Reference) 

Primary X-Ray Beam 

(Reference) 

X-Ray Source Position 

(Reference) 

VIEW 0-0 

Figure 1. Engine Beam X-Ray, Aft Engine Mount (Sheet 3) 

MEL-54-01 

Page 8 

March 20, 2015 
FWD t 

Penetrameter 

Figure 1. Engine Beam X-Ray, Aft Engine Mount (Sheet 4) 

March 20, 2015 

MEL-54-01 

Page 9 
Eddy Current 

Probe Access 

Eddy Current 

Probe Access 

Figure 2. Engine Beam Eddy Current, Forward Engine Mount (Sheet 1) 

MEL-54-01 

Page 10 

March 20, 2015 
March 20, 2015 

Eddy Current 

Probe Access 

.-----'--------J 

Figure 2. Engine Beam Eddy Current, Forward Engine Mount (Sheet 2) 

MEL-54-01 

Page 11 
MEL-54-01 

Page 12 

Lift-Off 

Figure 3. Eddy Current Calibration (Sheet 1) 

Minimum 

Sensitivity 

Level 

Null Point 

March 20, 2015 
Airplane Serial Left Engine Hours 

Number 

Total Airframe Hours Right Engine Hours 

Owner's Name Inspection Facility 

Name 

Owner's address Inspection Facility 

Address 

List all STC installed 

on the airplane 

In the table that follows please provide detailed and dimensioned descriptions of any crack(s). Attach pictures 

to this form as necessary. 
LEFT OUTBOARD ENGINE BEAM LEFT INBOARD ENGINE BEAM 

Was a crack found Yes/No? Was a crack found Yes/No? 

Detailed description: (Attach pictures and additional Detailed description: (Attach pictures and additional 

details as necessary) details as necessary) 

RIGHT INBOARD ENGINE BEAM RIGHT OUTBOARD ENGINE BEAM 

Was a crack found Yes/No? Was a crack found Yes/No? 

Detailed description: (Attach pictures and additional Detailed description: (Attach pictures and additional 

details as necessary) details as necessary) 

-

Send completed form/attachments to Cessna Structures at csstructures@txtav.com