Service Bulletin 644E supersedes Service Bulletin 644D in its entirety and voids Service Bulletin 534 completely. 

Aircraft that have previously complied with Service Bulletin 664D are already in compliance with Service Bulletin 

644E. Aircraft that have previously complied with Service Bulletin 534 must also comply with Service Bulletin 644E.

SUBJECT: TURBOCHARGER EXHAUST COUPLING 

INSPECTION/REPLACEMENT

REASON FOR REVISION: To add pressurized models PA-31P and PA-31P-350 and 

 rescind SB 534.

MODELS AFFECTED: SERIAL NUMBERS AFFECTED:

PA-31 and PA-31-325 Navajo 31-2 through 31-8312019

PA-31-350 Chieftain 31-5001 through 31-8452021

PA-31-350 T-1020 31-8253001 thru 31-8553002

PA-31P Pressurized Navajo 31P-1 through 31P-7730012

PA-31P-350 Pressurized Mojave 31P-8414001 through 31P-8414050

NOTE: All further references to PA-31-350 below apply to both the Chieftain and T-1020 models.

COMPLIANCE TIME:

Part I. All aircraft within ten (10) hours of operation or at the next scheduled inspection, whichever occurs first, 

determine the type of turbocharger exhaust coupling installed. If Turbocharger Exhaust Coupling, Piper part number 

(P/N) 555-511 or 555-366 (segmented type), inspect every one-hundred (100) hours time-in-service (TIS). Replace 

turbocharger exhaust coupling at one-thousand (1000) hours TIS.

NOTE: If Turbocharger Exhaust Coupling is Piper P/N 556-962 or 556-053, it is no longer an approved part 

and must be replaced with an approved exhaust coupling prior to further flight.

Part II. At Owner/Operator’s discretion, or when required by PART I.

Part III. Within the next ten (10) hours of operation or at the next regularly scheduled maintenance event, 

whichever occurs first.

APPROVAL: The technical content of this Service Document has been shown to comply with 

the applicable Federal Aviation Regulations and is FAA approved.

PURPOSE: Field reports indicate several service problems associated with turbocharger to 

tailpipe couplings. A field investigation into the cause has revealed that in many 

instances the recommended maintenance, inspection, and torquing procedures 

in this very important part of the exhaust system have not been followed. The 

failure of a turbocharger to tailpipe coupling may allow hot turbocharger exhaust 

gases to be expelled into the coupling area, creating a fire hazard.

 SERVICE NO. 644E

 BULLETIN

PIPER CONSIDERS

COMPLIANCE MANDATORY

Piper Aircraft, Inc.

2926 Piper Drive

Vero Beach, Florida, U.S.A. 32960

Date: May 9, 2012 (M)

ATA: 8123

(OVER)
SERVICE BULLETIN NO. 644E PAGE 2 of 6

PART I of this Service Bulletin provides instructions for a more detailed inspection and torquing of the segmented 

type Turbocharger Tailpipe Coupling, Piper P/N 555-511 or 555-366, at each one-hundred (100) hours; requires the 

use of the revised One-Hundred Hour Inspection Forms; and requires that coupling be replaced at one-thousand 

(1,000) hours of coupling TIS.

PART II announces the availability of a new, heavy-duty field tested turbocharger exhaust coupling that, when 

installed, relieves the Inspection Requirement of PART I and the one-thousand (1,000) hour mandatory replacement.

NOTE: Compliance with PART II also relieves the one-thousand (1,000) hour replacement requirements 

called for in the PA-31 and PA-31-325 Navajo Service Manual, P/N 753-704; in the PA-31-350 

Chieftain Service Manual, P/N 761-488; in the PA-31P Pressurized Navajo Service Manual, P/N 753-

770; and in the PA-31P-350 Pressurized Mojave Maintenance Manual, P/N 761-781.

NOTE: The requirements for compliance with this Service Bulletin will vary according to the V-band Coupling 

part number that is installed on each engine. See TABLE 1 for a summary of these requirements.

Part I.

INSTRUCTIONS:

Refer to the latest revision of the following Piper Aircraft Inspection Reports:

1. Within the next ten (10) hours of operation, determine type of turbocharger exhaust coupling installed:

a. If single-piece type, Piper P/N 556-962 (PA-31, PA-31-325) or 556-053 (PA-31-350, PA-31P, PA-31P-350), 

replacement is required prior to further flight. Proceed to Part II.

b. If segmented-type, Piper P/N 555-511 (PA-31, PA-31-325) or 555-366 (PA-31-350, PA-31P, PA-31P-350), 

proceed to Instruction 2 below, in accordance with Compliance Time, Part I.

2. Remove upper engine cowlings.

3. Remove turbocharger exhaust couplings. Inspect couplings for cracks, spreading of sides, and indication of 

exhaust pipe flanges bottoming in coupling. (Refer to Sketch “A” attached). Inspect coupling clamp bolt for 

bending, overstress and cracks. (Refer to Sketch “A”.)

CAUTION: ANY TIME AN EXHAUST SYSTEM COMPONENT IS INSTALLED OR REMOVED, USE 

CAUTION NOT TO SPREAD OR FORCE THE COUPLING BEYOND ITS NORMAL OPEN 

POSITION. TO DO SO WILL EITHER DISTORT ITS SHAPE AND CAUSE AN INEFFECTIVE 

SEAL OR IT WILL DAMAGE THE METAL AND RESULT IN EVENTUAL FAILURE OF THE 

COUPLING.

4. Inspect turbocharger exhaust pipe flange area for proper mating of surfaces and for leaks. Inspect flanges for 

cracks and distortion. Carbon deposits should be removed from mating flanges before reassembly.

5. Should any parts of the above inspection reveal any of the described faults, the failed component(s) must be 

replaced before further flight.

6. Reinstall turbocharger exhaust pipe and coupling onto the tailpipe assembly and turbocharger.

NOTE: Waste gate exhaust clamps should be loosened to facilitate installation of the exhaust pipe and insure 

proper alignment of exhaust flanges without unnecessary strain on exhaust system components.

7. Install coupling on exhaust flange and torque nut in accordance with Sketch “A” while tapping gently around the 

periphery with a soft mallet to distribute band tension.

PA-31, PA-31-325 Piper Part No. 230-211

PA-31-350 Piper Part No. 230-764

PA-31P-350 Piper Part No. 230-1088

PA-31P Piper Service Manual P/N 753-770, Section III
SERVICE BULLETIN NO. 644E PAGE 3 of 6

PART II.

INSTRUCTIONS:

1. Remove upper engine cowlings.

2. Remove turbocharger exhaust couplings and discard.

3. Inspect turbocharger exhaust pipe flange area for proper mating of surfaces and for leaks. Inspect flanges for 

cracks and distortion. Carbon deposits should be removed from mating flanges before reassembly.

4. Install new style exhaust couplings. (See MATERIAL REQUIRED.)

NOTE: Waste gate exhaust clamps should be loosened to facilitate installation of exhaust pipe and insure 

proper alignment of exhaust flanges without unnecessary strain on exhaust system components.

5. Tighten couplings to torque value of 30 in-lbs minimum, 35 in-lbs maximum. Tap gently around the periphery 

with a soft mallet to distribute band tension. Recheck torque.

6. Secure and tighten waste gate exhaust clamps previously loosened per NOTE above.

7. Inspect couplings for positive clearance between safety latch and “T” bolt, and between coupling segments 

after final torque. See Sketch “B” attached.

8. Reinstall upper engine cowlings.

9. Make appropriate logbook entry of compliance with PART II of this Service Bulletin.

8. Turbocharger to tailpipe coupling with one-thousand (1,000) hours or more TIS must be replaced. (See 

MATERIAL REQUIRED.)

NOTE: If a coupling has more than one-thousand (1,000) hours TIS, and if a new coupling is not immediately 

available, the existing coupling may be continued in use for up to an additional two-hundred (200) 

hours if the coupling is inspected for cracks every twenty-five (25) hours without removal with a 10X 

magnifying glass. This twenty-five (25) hour inspection requirement does not relieve the one-hundred 

(100) hour inspection requirement for couplings with Piper P/N 555-511 or 555-366.

9. Reinstall upper cowling.

10. Make appropriate logbook entry of compliance with PART I of this Service Bulletin.

PART III.

INSTRUCTIONS:

1. If Turbocharger Exhaust Couplings, Piper P/N 557-584 and 557-369 have been installed prior to the date of this 

publication and PART II has not been previously completed, comply with the following instructions.

2. Remove upper cowlings on left and right engines.

3. Inspect couplings for positive clearance between safety latch and “T” bolt, and between coupling segments, 

after final torque. See Sketch “B” attached.

4. Inspect couplings for security and that “T” bolt is not bottomed out.

5. If couplings are found to be distorted and/or bottomed out, replacement is required. (See MATERIAL 

REQUIRED.)

6. Reinstall upper cowlings on left and right engines.

7. Make appropriate logbook entry of compliance with PART III of this Service Bulletin.
MATERIAL REQUIRED: Two (2) each Couplings, Piper P/N 557-584 for PA-31 and PA-31-325. 

Two (2) each Couplings, Piper P/N 557-369 for PA-31-350, PA-31P, PA-31P-350.

AVAILABILITY OF PARTS: Your Piper Service Facility.

EFFECTIVITY DATE: This Service Bulletin is effective upon receipt.

SUMMARY: Please contact your Factory Authorized Piper Service Facility to arrange for 

compliance with this Service Bulletin in accordance with the Compliance Time 

indicated above.

NOTE: Please notify the factory of any address/ownership corrections. Changes should include aircraft model, 

serial number, current owner’s name and address.

Corrections and/or changes should be directed to:

 PIPER AIRCRAFT, INC.

Attn: Customer Service

2926 Piper Drive

 Vero Beach, FL 32960

SERVICE BULLETIN NO. 644E PAGE 4 of 6

Aircraft Model Piper V-band Applicable Maintenance Action Summary

 Coupling P/N Sketch

 556-962 n/a Replace prior to next flight. 

 PA-31 Navajo 555-511 Sketch A Inspect every 100 hrs TIS.

 PA-31-325 Navajo Replace upon reaching 1,000 hrs TIS.

 Routine inspection per Service Manual

 557-584 Sketch B instructions. Replace on condition. 

 (no life limit)

 

 556-053 n/a Replace prior to next flight.

 PA-31-350 Chieftain 

 PA-31-350 T-1020 555-366 Sketch A Inspect every 100 hrs TIS.

 PA-31P Pressurized Navajo Replace upon reaching 1,000 hrs TIS.

 PA-31P-350 Pressurized Mojave 

 Routine inspection per Maintenance 

 557-369 Sketch B Manual/Service Manual instructions.

 Replace on condition. (no life limit)

 

Summary of compliance requirements for this Service Bulletin.

Read the entire Service Bulletin to obtain complete instructions.

TABLE 1
SERVICE BULLETIN NO. 644E PAGE 5 of 6

Inspect Tailpipe and Turbocharger

Flanges for proper mating

Tailpipe

COUPLING - Refer

to Chart for correct

P/N and Proper Torque

Inspect Turbocharger

Flange for carbon

deposits, cracks

and distortion

Inspect Coupling Bolt

for bends, distortion,

cracks and thread

damage

Inspect Coupling Strap

for cracks, separation

and distortion

Inspect Coupling V Bands

for cracks, separation from

strap and distortion

Inspect Tailpipe Flange

for carbon deposits,

cracks and distortion

VIEW LOOKING AFT AT TURBOCHARGER

Torque the coupling in accordance with this chart

Model Clamp P/N Torque

 PA-31-350, PA-31P, PA-31P-350 555-366 (MVT68049-450M) 45-55 in-lbf

 PA-31, PA-31-325 555-511 (MVT69861-377M) 40-50 in-lbf

SKETCH “A”
SERVICE BULLETIN NO. 644E PAGE 6 of 6

“T” Bolt Retaining 

Strap

After installation and Final Torque to 35 in-lbs,

Positive Clearance must be evident between

Safety Latch and “T” Bolt 

Positive clearance

V BAND CLAMPING DETAILS

Safety Latch

Torque the coupling in accordance with this chart

Model Clamp P/N Torque

 PA-31-350, PA-31P, PA-31P-350 557-369 (NH1005798-10) 30-35 in-lbf

 PA-31, PA-31-325 557-584 (NH1005834-10) 30-35 in-lbf

SKETCH “B”