NUMBER 

## ENGINEERING

REPORT # 281 SNOW ENGINEERING CO.

W ICHITA F ALLS , T EXAS


### ORDE R X MODEL

TITLE BY CHK’D 

### See Below

D avid Li g on L S SERIAL

DATE 

### SERVICE LETTER #281

PAGE OF 

### 0 8/01/09 1 1 2

SUBJECT:

Split Sleeve Cold Expansion of Lower Spar Cap Holes - Rework of In-service Aircraft in the 9-hole Configuration

MODELS:

AT-802, AT-802A S/N 802-0092 through 802-0269

REFERENCE:

(1) – Fatigue Technology Inc. Process Specification 8101D (2) - Snow Engineering Co. Drawing 20995, sheet 3

GENERAL:

This Service Letter provides a set of detailed instructions for cold working the 2 outboard-most wing center splice block holes in the lower spar cap. This document addresses airplanes in the 8 hole block configuration.

For clarification, the splice block bolt holes are numbered from inboard to outboard. The inboard-most hole is defined as the “#1 Hole” and the outboard-most hole is defined as the “#9 Hole”. See Figure 1 below. The terms “#9 Hole” and “#8 Hole” will be used throughout this document to identify holes being cold worked.

**Figure 1** - 9 Hole Block Numbering Scheme



### CAUTION:
A MIS-DRILLED OR MIS-REAMED HOLE WILL RUIN THE SPAR CAP. THERE IS NO
FIX FOR AN OVERSIZED OR EGG-SHAPED HOLE. OVERSIZED OR EGG-SHAPED HOLES WILL REQUIRE SPAR CAP REPLACEMENT. REPLACING A DAMAGED SPAR
CAP CAN LEAD TO SIGNIFICANT COST AND SIGNIFICANT AIRCRAFT DOWNTIME.
EXERCISE EXTREME CAUTION AND GOOD AVIATION MAINTENANCE PRACTICES AND TECHNIQUE WHEN PERFORMING THE STEPS IN THIS SERVICE LETTER.NUMBER 

## ENGINEERING

REPORT # 281 SNOW ENGINEERING CO.

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### ORDE R X MODEL

TITLE BY CHK’D 

### See Below

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### SERVICE LETTER #281

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EQUIPMENT:

The tools required to accomplish this rework are separated into 3 different
tool kits and are color coded for ease of identification. The “Yellow” Tool Kit A is used when cold working the “#9 Holes”. The “Blue” Tool Kit B is used when cold working the “#8 Holes”. The “Red” Tool Kit C contains all other general tools used for this process. The instructions in this document specify that each hole size be worked separately. This is not only to eliminate opportunities for tool selection errors, but also to hold the spar cap stackup in place during the cold working process. While working from the “Yellow” tool kit, the “Blue” tool kit should be closed, latched, and out of reach. While working from the “Blue” tool kit, the “Yellow” tool kit should be closed, latched, and out of reach.

P/N DESCRIPTION CASR-60-1 Starting Reamer

CAG-60 Combination Gage CAMG-60 Mandrel Gage
CAS-60-36F Flared Sleeve (2 ea.)

CAM-60-2-60-V2 Mandrel MEN-26B-1223F Nosecap Assembly CAR-60-1-.3750 Gage Finish Reamer

Table 1 – **Cold Work Tool Kit List** – 3/8 Finished Holes (STDN = 60)

P/N DESCRIPTION CASD-80-1-C Starting Drill (Ref .453 Dia)

CASR-80-1 Starting Reamer (Ref .470 Dia.)

CAG-80 Combination Gage CAMG-80 Mandrel Gage
CAS-80-40F Flared Sleeve (2 ea.)

CAM-80-2-60-V2 Mandrel MEN-26B-1601F Nosecap Assembly CAR-80-1-.5000 Gage Finish Reamer

Table 2 – **Tool Kit B “Blue Tool Kit”** – 1/2 Finished Holes (STDN = 80)

P/N DESCRIPTION

MB-30 Medium Brute Puller Unit

FT-20 Power Pak PS200-1 120 microinch surface finish comparator plate SK398-1 Cold Work Tooling Fixture (See SK398-1 for complete list of parts)

Table 3 – **Tool Kit C “Red Tool Kit”** – General ToolsNUMBER 

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DATE 

### SERVICE LETTER #281

PAGE OF 

### 0 8/01/09 3 1 2

PERSONNEL QUALIFICATION:

In order to perform the steps in this Service Letter, personnel must:
a.) possess the tooling specified in the “Equipment” section of this

document. b.) be trained and certified for eddy current inspection.
c.) attend an Air Tractor sponsored training course and receive a certificate of completion for the Split Sleeve Cold Expansion process. This requirement may also be fulfilled by attending a Fatigue Technology Inc. training session and receiving a Certificate of Training after the completion of that training.

PROCEDURE:

**SECTION A - CLEAN AND GAIN ACCESS TO REPAIR AREA**

B. 1. Before accomplishing this Service Letter, thoroughly clean the airplane, especially the hopper, gatebox, and wing splice area.

B. 2. Gain access to the repair area as follows:

B. 2.1. Remove hopper dump push rod mechanism

B. 2.2. Remove spray pump to spray valve tube

B. 2.3. Remove bottom load fill tube

B. 2.4. Remove spray pump supply tube

B. 2.5. Remove gatebox fairing

B. 2.6. Remove gatebox
B. 2.7. Remove fiberglass enclosure skin

**SECTION B - REMOVE HARDWARE, INSPECT #7 AND #8 HOLES**

B. 1. Shore aircraft wings as follows:

B. 1.1. Place wing jacks at wing tie-down ring locations.

B. 1.2. Simultaneously raise both jacks until jack pads “just contact” the tie-down ring on both left and right wings.

B. 1.3. Simultaneously raise both jacks an additional 11/16 + 1/16 to unload the bolts in the lower cap splice connection and
facilitate bolt removal.

B. 2. Identify the spar lower cap “#8 and #9 hole” bolt locations. See Figure 1.

B. 3. Remove nuts from the two 3/8 bolts, both left and right side, in the lower wing spar splice using good aviation maintenance practice. Use 1/4” aluminum pin punch to CAREFULLY tap bolts up and out of lower spar cap and splice blocks.

NOTE: USE EXTREME CAUTION NOT TO SCRATCH INSIDE OF HOLES WITH PUNCH.

B. 4. Remove nuts from the two 7/16 bolts, both left and right side, in the lower wing spar splice using good aviation maintenance practice.NUMBER 

## ENGINEERING

REPORT # 281 SNOW ENGINEERING CO.

W ICHITA F ALLS , T EXAS


### ORDE R X MODEL

TITLE BY CHK’D 

### See Below

D avid Li g on L S SERIAL

DATE 

### SERVICE LETTER #281

PAGE OF 

### 0 8/01/09 4 1 2

Use 1/4” aluminum pin punch to CAREFULLY tap bolts up and out of lower spar cap and splice blocks.

NOTE: USE EXTREME CAUTION NOT TO SCRATCH INSIDE OF HOLES WITH PUNCH.

B. 5. Clean #8 and #9 holes using solvent and a soft bristle brush or rag. Use compressed air to remove all solvent residue from the holes.

B. 6. Eddy Current inspect “#8 and #9 Holes” per Air Tractor PS 197.

**SECTION C – COLD WORK #8 AND #9 HOLES**

C. 1. Install and locate SK398-1 attach block Tooling Fixture (See SK398):

C. 1.1. Remove the two #3 5/8” dia. bolts from the center splice. Install the tooling fixture with two 5/8” dia. studs, nuts, and washers as shown on SK398. Tighten the stud nuts.

C. 1.2. Install drill press onto the drill press mounting plate. Do not tighten 2 mounting bolts.

C. 1.3. Lock Tapered Alignment Pin into drill chuck.

C. 1.4. Position drill press so alignment pin slips into hole.

C. 1.5. With Tapered Pin still in hole, tighten 2 mounting bolts.

C. 1.6. Withdraw drill chuck from hole and remove alignment pin.

C. 1.7. Drill fixture is now aligned with hole.

COLD WORK “#9 HOLE” TO 3/8 (STANDARD TOOL DIAMETER NUMBER, STDN = 60)

Note: Accomplish the following Cold Work steps concurrently for both the left hand and right hand “#8 Holes”.

C. 2. Acquire “3/8 Cold Work Kit A and inventory for proper tools using

Table 1.
C. 3. Ream the “#9 Hole” using the CASR-60-1 starting reamer. Sulfur based cutting oil should be used for starting hole ream and all subsequent ream steps. After reaming, move SK398-1 Tooling Fixture out of the way and clean the hole with solvent and dry with compressed air. See Figure 2. IMPORTANT!
IF BOTH #8 HOLES AND BOTH #9 HOLES PASS THE EDDY CURRENT INSPECTION IN PS 197, PROCEED WITH THE STEPS IN THIS SERVICE LETTER. IF ANY HOLES
FAIL THE EDDY CURRENT IN SPECTION IN PS 197, DISCONTINUE THIS SERVICE
LETTER.NUMBER 

## ENGINEERING

REPORT # 281 SNOW ENGINEERING CO.

W ICHITA F ALLS , T EXAS


### ORDE R X MODEL

TITLE BY CHK’D 

### See Below

D avid Li g on L S SERIAL

DATE 

### SERVICE LETTER #281

PAGE OF 

### 0 8/01/09 5 1 2

C. 4. The starting hole diameter must be .348-.351. Check the starting hole using the CAG-60 Go-No Go Combination Gage, or a ball gage and micrometer. When using the Go-No Go Combination Gage, a gage that can only be inserted to the first machined “step” identifies a properly reamed hole. The starting hole should be checked for
ovality by inserting the gage a second time, rotated 90  . See Figure

3.

C. 5. Select the CAM-60-2-60-V2 mandrel and inspect using the CAMG-60 GoNo Go gage or a micrometer. The mandrel major diameter shall be .3428 - .3438. The mandrel shall be checked at the beginning of each aircraft job because the mandrel diameter is critical for proper cold expansion of the hole. An excessively worn mandrel will pass through the CAMG-60 Go-No Go gage and shall be replaced. If the mandrel fails the diameter check, contact Air Tractor Customer Service Department for a replacement mandrel. See Figure 4.

C. 6. Clean the hole using solvent and a soft bristle brush or rag. Use compressed air to remove all solvent residue from the holes. Mandrel Check Fixture Mandrel Check

Reject and Discard Mandrel A ccept



### Figure 4 A ccept Reject



### Fi g ure 3 Starting Drill

Starting Reamer



### Figure 2NUMBER 

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### ORDE R X MODEL

TITLE BY CHK’D 

### See Below

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### SERVICE LETTER #281

PAGE OF 

### 0 8/01/09 6 1 2

C. 7. Cold expand the hole. See Figure 5:

C. 7.1. Select the CAS-62-30F split sleeve and slide it over the mandrel. Orient sleeve so that the split is pointing along the spar cap centerline facing inboard and the flared end is toward the Puller nosecap.

C. 7.2. Insert the mandrel and sleeve into the starting hole. Ensure sleeve orientation is correct per step 13.1 above. The sleeve should protrude from the topside of the hole
1/32” or more.
C. 7.3. Place nosecap firmly against and perpendicular to the lower surface of the splice block.

C. 7.4. Activate Puller. Continue holding the trigger until mandrel is through the entire lower spar cap stackup. Release trigger when the mandrel is clear of the structure.

C. 7.5. Remove sleeve from the cold worked hole and discard. **Sleeves are used only once.**

C. 8. Check the cold expanded hole diameter using the CAG-60 Go-No Go Combination gage. The gage will fit into a properly expanded hole.
The cold worked hole should measure .3530 as a **minimum** before the finish ream process. If the Go-No Go Combination gage will not fit 

### Figure 5 SPLIT FACES
INBOARDNUMBER 

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### SERVICE LETTER #281

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into the hole, check for proper tool selection, check mandrel for proper diameter, then follow step 13 a second time. Note that a surface upset is created during the cold working process at each hole face. This surface upset is normal. See Figure 6.

C. 9. Follow the Tooling Fixture alignment procedure previously described.

C. 10. Finish ream the cold worked hole using the CAR-60-1-.3750 gage
finish reamer. Finish reamed final hole must have a surface roughness of 120 microinches or smoother measured with surface finish comparator plates. See Figure 7.

C. 11. Inspect finished hole. Finish reamed final hole must have a diameter of .3750 +.002 / -.000 and must have a surface roughness of Gage Finish Reamer Go-No-Go Gage

Combination Gage

or or Hole has been cold expanded.

Hole has not been cold expanded. Gage Finish Reamer



### Fi gu r e 6

Finish Reamer



### Figure 7NUMBER 

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W ICHITA F ALLS , T EXAS


### ORDE R X MODEL

TITLE BY CHK’D 

### See Below

D avid Li g on L S SERIAL

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### SERVICE LETTER #281

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### 0 8/01/09 8 1 2

120 microinches or smoother measured with surface finish comparator plates. Holes may be inspected using a ball gauge and micrometer, or air gauge with the proper calibrated hole standards.

C. 12. Install new hardware in accordance with Drawing 20995, sheet 3.

**SECTION 3 - REMOVE HARDWARE, INSPECT, COLD WORK “#8 HOLE” TO 1/2 HOLE**
**(STANDARD TOOL DIAMETER NUMBER, STDN = 80)**

C. 13. Acquire “Blue” Tool Kit B and inventory for proper tools using Table

2.
C. 14. Identify the spar lower cap “#8 Hole” bolt locations. See Figure 1.

C. 15. Remove clamp bolts at #7 hole locations.

C. 16. Clean holes using solvent and a soft bristle brush or rag. Use compressed air to remove all solvent residue from the holes.

C. 17. Follow the Tooling Fixture alignment procedure previously described.

C. 18. Drill the entire stackup of upper and lower blocks and lower cap at the “#8 Hole” location using CASD-80-1-C starting drill. Sulfur based cutting oil should be used for starting hole drill and all subsequent ream steps.
C. 19. Ream the “#8 Hole” using the CASR-80-1 starting reamer. After reaming, move SK398-1 Tooling Fixture out of the way and clean the hole with solvent and dry with compressed air. See Figure 8.

C. 20. The starting hole diameter must be .470 - .473. Check the starting hole using the CAG-80 Go-No Go Combination Gage, or a ball gage and micrometer. When using the Go-No Go Combination Gage, a gage that can only be inserted to the first machined “step” identifies a properly reamed hole. The starting hole should be checked for
ovality by inserting the gage a second time, rotated 90  . See Figure

9. Starting Drill

Starting Reamer 

### Figure 8NUMBER 

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REPORT # 281 SNOW ENGINEERING CO.

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TITLE BY CHK’D 

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### SERVICE LETTER #281

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### 0 8/01/09 9 1 2

C. 21. Select the CAM-80-2-60-V2 mandrel and inspect using the CAMG-80 GoNo Go gage or a micrometer. The mandrel major diameter shall be .4643-4653. The mandrel shall be checked at the beginning of each aircraft job because the mandrel diameter is critical for proper cold expansion of the hole. An excessively worn mandrel will pass through the CAMG-80 Go-No Go gage and shall be replaced. If the mandrel fails the diameter check, contact Air Tractor Customer Service Department for a replacement mandrel. See Figure 10.

C. 22. Clean the hole using solvent and a soft bristle brush or rag. Use compressed air to remove all solvent residue from the holes.

C. 23. Cold expand the hole. See Figure 11:

C. 23.1. Select the CAS-80-36F split sleeve and slide it over the mandrel. Orient sleeve so that the split is pointing along A ccept Reject



### Figure 9

Mandrel Check Fixture Mandrel Check

Reject and Discard Mandrel A ccept



### Figure 10NUMBER 

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### SERVICE LETTER #281

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the spar cap centerline facing inboard and the end is toward the Puller nosecap.
C. 23.2. Insert the mandrel and sleeve into the starting hole. Ensure sleeve orientation per step 29.1 above. The sleeve should protrude from the topside of the hole 1/32” or more.

C. 23.3. Place nosecap firmly against and perpendicular to the lower surface of the splice block.

C. 23.4. Activate Puller. Continue holding the trigger until mandrel is through the entire lower spar cap stackup. Release trigger when mandrel is clear of the structure.

C. 23.5. Remove sleeve from the cold worked hole and discard. **Sleeves are used only once.**

C. 24. Check the cold expanded hole diameter using the CAG-80 Go-No Go Combination gage. The gage will fit into a properly expanded hole.
The cold worked hole should measure .4780 as a **minimum** before the finish ream process. If the Go-No Go Combination gage will not fit into the hole, check for proper tool selection, check mandrel for proper diameter, then follow step 30 a second time. Note that a 

### Fi g ure 11 SPLIT FACES INBOARDNUMBER 

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surface upset is created during the cold working process at each hole face. This surface upset is normal. See Figure 12.

C. 25. Follow the Tooling Fixture alignment procedure previously described.

C. 26. Finish ream cold worked hole using CAR-80-1-.5000 gage finish reamer. Finish reamed final hole must have a surface roughness of 120 microinches or smoother measured with surface finish comparator plates. See Figure 13.

C. 27. Inspect finished hole. Finish reamed final hole must have a diameter of .4995 +.002 / -.000 and must have a surface roughness of 120 microinches or smoother measured with surface finish comparator Gage Finish Reamer Go-No-Go Gage

Combination Gage

or or Hole has been cold expanded.

Hole has not been cold expanded. Gage Finish Reamer



### Figure 12

Finish Reamer



### Figure 13NUMBER 

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### 0 8/01/09 12 1 2

plates. Holes may be inspected using a ball gauge and micrometer, or air gauge with the proper calibrated hole standards.

C. 28. Install new hardware in accordance with Drawing 20995, sheet 1.

**SECTION 4 - REASSEMBLE AIRPLANE AND RETURN TO SERVICE**

C. 29. Reinstall gatebox and all equipment removed in accordance with Airplane Owners Manual.

C. 30. Make the following maintenance log entry in aircraft logbook:

“This aircraft, Air Tractor (model number) -(s/n) , has been reworked in accordance with Snow Engineering Co. Service Letter #281 and is approved for return to service, this date (date) , signed (signature) , (certificate and number).