SYNOPSIS
CH-47-93-ASAM-04 AVIATION SAFETY ACTION MESSAGE, INFORMATIONAL, ALL
CH-47 AND MH-47 SERIES AIRCRAFT, MAINTENANCE INFORMATION
FOR T-55-L-712 ENGINES.
201730Z APR 93, BRAD MEYER, AMSAT-C-XS, X2085.
NOTE: Enter a <Q> to exit or <SPACEBAR> to view the
entire message.
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01 12 201730Z APR 93 PP PP UUUU
:CDRATCOM ST LOUIS MO //AMSAT-C-XS//
TO
:AIG 6713
:AIG 9004
:AIG 8708
:AIG 9042
:DEFARM CANBERRA AS //DOHS-A//
:DEFNAV CANBERRA AS
:CDRUSARDSG CANBERRA AS
:HQLCENG MELBOURNE AS //DAIRENG//
:LOG CON OTTAWA ONT CAN //DTHEM 6-3//
:AUSTNAV WASHINGTON DC //DEFNAV//
:AUSTAIR WASHINGTON DC //SENGSO//
:USOMC CAIRO EG //AV//
:ODC ATHENS GR //ODCSA-A//
:CDR4THBN228THAVN SOTO CANO HO //AVN-AMO//
:CDR160TH SOAR FT CAMPBELL KY //AOAV-SI//
:CDRBGAD RICHMOND KY //SDSBG-GC//
:CHMUSLO RABAT MO //AF//
:CHUSAS RIYADH SA //ASAV//
:ODC MADRID SP //ARMY AND NAVY SEC//
:CJUSMAG BANGKOK TH
:CDRUSARDSG LONDON UK //AMXSN-UK-SE//
INFO
:CDRAMCCOM ROCK ISLAND IL //AMSAR-QAS-P//
:CDRAMC ALEXANDRIA VA //AMCMR/AMCCS/AMCSM-WAA//
XMT
:USDAO DHAKA BG
:USDAO RANGOON BM
:USDAO COLUMBO CE
:USDAO SUVA FJ
:OMADP JAKARTA ID
:DSA NEW DELHI IN
:USDAO ANTANANARIVO MA
:SAO KUALA LUMPUR MY
:USDAO KATMANDU NP //SAO//
:USDAO SINGAPORE SN //SAO//
:UNCLAS RELEASABLE TO NATO ADDRESSEES
:AIG 9004 TAKE FOR INFO ONLY
:AIG 8708 TAKE FOR INFO ONLY
:AIG 9042 TAKE FOR INFO ONLY
:UNCLAS
SUBJECT - AVIATION SAFETY ACTION MESSAGE, INFORMATIONAL, RCS
CSGLD-1860(R1), ALL CH-47 AND MH-47 SERIES AIRCRAFT, MAINTENANCE
INFORMATION FOR T55-L-712 ENGINES (CH-47-93-ASAM-04).
NOTE - THIS IS AN AVIATION SAFETY ACTION MESSAGE ISSUED PER AR 95-3,
CHAPTER 5 REVISION VIA MESSAGE HQ AVSCOM, AMSAV-XSOF, 181900Z SEP
90, SUBJECT: CHANGE TO AR 95-3, CHAPTER 5, SAFETY OF FLIGHT
MESSAGES. THIS MESSAGE HAS NOT BEEN TRANSMITTED TO UNITS
SUBORDINATE TO ADDRESSEES. ADDRESSEES SHOULD IMMEDIATELY RETRANSMIT
THIS MESSAGE TO ALL SUBORDINATE UNITS, ACTIVITIES OR ELEMENTS
AFFECTED OR CONCERNED. THE RETRANSMITTAL SHALL REFERENCE THE
MESSAGE. ACTION ADDRESSES WILL IMMEDIATELY VERIFY THIS
RETRANSMISSION TO COMMANDER, ATCOM, ATTN - AMSAT-C-XS (SOF
COMPLIANCE OFFICER).
1. PRIORITY CLASSIFICATION - N/A.
2. TASK/INSPECTION SUSPENSE DATE - N/A.
3. REPORTING COMPLIANCE SUSPENSE DATE - N/A.
4. SUMMARY OF PROBLEM -
A. THERE HAVE BEEN NUMEROUS INCIDENTS OF HUNG STARTS
(FAILURE OF THE ENGINE TO ACCELERATE TO GROUND IDLE WITH HIGH PTIT)
AND N1 ROLLBACK (UNCOMMANDED DECELERATION OF GAS PRODUCER TURBINE)
WHICH HAVE BEEN INVESTIGATED AND ANALYZED.
B. THE PURPOSE OF THIS MESSAGE IS TO INFORM THE USER OF
ACTIONS TAKEN, APPROPRIATE MAINTENANCE PROCEDURES, AND OTHER
FORTHCOMING MANUAL CHANGES.
5. END ITEMS AFFECTED - ALL CH-47 AND MH-47 SERIES AIRCRAFT.
6. ASSEMBLY COMPONENTS TO BE INSPECTED -
NOMENCLATURE PART NO. NSN
T55-L-712 ENGINE 2-001-020-23 2840-01-030-4890
7. PARTS TO BE INSPECTED - N/A.
8. INSPECTION PROCEDURES - ENGINES THAT HAVE EXHIBITED HUNG STARTS
OR N1 ROLLBACKS SHOULD USE THE PROCEDURES IN PARAGRAPH 9.
9. CORRECTION PROCEDURES -
A. THE CAUSE OF HUNG STARTS CAN BE ATTRIBUTED TO A NUMBER OF
ITEMS BUT MAINLY THE CONDITION OF THE COMPRESSOR, IMPROPER ENGINE
BLEED AND THE FUEL FLOW DURING THE STARTING SEQUENCE. A
TROUBLESHOOTING GUIDE (PAGE 1-218, CHANGE 7) TO ENHANCE MAINTENANCE
ACTIONS AND A PROCEDURE TO ADJUST THE JP-4/JP-5 FUEL SELECTOR SWITCH
(PAGE 1-528, CHANGE 7) HAS BEEN ADDED TO THE TM 55-2840-254-23. A
REVISED STARTING PROCEDURE AND ACCELERATION CHECK HAS BEEN ADDED TO
THE TM 55-1520-240-10 AND MAINTENANCE TEST FLIGHT MANUAL. IN
ADDITION TO THE ADDED PROCEDURES, SPECIAL ATTENTION SHOULD BE GIVEN
TO THE FOLLOWING ITEMS:
(1) ASSURE THAT THE COMPRESSOR BLEED BAND IS CLOSED
DURING COMPRESSOR WASHES AND COMPLY WITH THE SPECIFIED SOAKING
PERIOD. FAILURE TO CLOSE THE BLEED BAND GREATLY REDUCES THE
EFFECTIVENESS OF THE WASH, ESPECIALLY THE LAST FEW STAGES OF THE
COMPRESSOR.
(2) ASSURE THAT THE BLEED BAND STROKE IS AT LEAST ONE
INCH. THE COMPRESSOR IS VERY SENSITIVE TO PROPER BLEED FLOW DURING
STARTING AND A SHORT BLEED BAND STROKE MAY INDUCE A HUNG START.
ADJUST THE BLEED BAND STROKE TO MAXIMUM POSSIBLE OPENING (PROVIDED
THE BLEED BAND CLOSES COMPLETELY) TO ALLOW AS MUCH BLEED FLOW AS
POSSIBLE.
(3) ASSURE THAT THE BLEED BAND ACTUATOR IS SERVICEABLE
UTILIZING THE TWO GAUGE METHOD DESCRIBED IN PARAGRAPH 9B1.
(4) ADJUST THE FUEL SELECTOR SWITCH AND/OR MAKE AN
ACCELERATION SCHEDULE CHANGE IF THE CAUSE OF THE HUNG START IS
DETERMINED TO BE FUEL FLOW RELATED.
(5) IF THE HUNG START OCCURS DURING HOT RESTARTS, MOTOR
THE ENGINE UNTIL PTIT IS BELOW 200C BEFORE MOVING THE START SWITCH
TO START.
(6) ASSURE THAT THERE IS NO LEAKAGE OF AIR, SUCH AS
LEAKING P3 AIR LINE OR STUCK OPEN COMBUSTOR DRAIN VALVE, DURING
STARTING.
B. THE CAUSE OF RECENT N1 ROLLBACKS HAS BEEN ATTRIBUTED TO
BLEED BAND ACTUATORS THAT HAVE INTERNAL LEAKAGE THAT ALLOWS THE
BLEED BAND ACTUATOR TO REMAIN CLOSED, OR OPEN VERY SLOWLY, WHEN THE
BLEED BAND SHOULD BE OPENED UPON DECELERATION. THE ACTUATOR CAN BE
CHECKED UTILIZING THE TWO GAUGE METHOD AS FOLLOWS:
(1) CONNECT A 50 PSIG AIR SOURCE AND 0-100 PSIG
PRESSURE GAUGE INTO THE P3 PORT OF ACTUATOR AS FOLLOWS. CONNECT
0-100 PSIG PRESSURE GAUGE INTO PM PORT OF ACTUATOR. MAKE SURE PM
GAUGE OUTLET IS PLUGGED AND NO LEAKAGE EXISTS. PRESSURIZE P3 PORT
TO 50 PSIG. IF PM PRESSURE EQUALS OR EXCEEDS 45 PSIG, REPLACE THE
ACTUATOR.
(2) IN ADDITION, A N1 ROLLBACK IS POSSIBLE IF THE OLDER
CONFIGURATION FUEL CONTROLS (PRIOR TO THE -64/68 CONFIGURATIONS) ARE
RIGGED SO THAT THE MINIMUM N2 STOP IS LESS THAN 10 DEGREES AS IS
SOMETIMES NECESSARY ON CH-47C AIRCRAFT. THE LATEST CONFIGURATION
FUEL CONTROLS (-64/68) ARE CALIBRATED AT THE 5 DEGREE STOP TO BE
ACCEPTABLE ON EITHER CH-47C OR D AIRCRAFT. THE OLDER CONFIGURATIONS
WERE ONLY CALIBRATED AT THE 15 DEGREE SETTING FOR USE ON THE CH-47D
AIRCRAFT.
C. ATCOM IS CURRENTLY QUALIFYING A FUEL CONTROL THAT HAS A
REDUCED FUEL FLOW SCHEDULE DURING STARTING. AN ENHANCED BLEED BAND
ACTUATOR, 2-160-350-35 WAS RELEASED THAT SHOULD BE MORE DURABLE AND
LESS SUSCEPTIBLE TO INTERNAL LEAKAGE. A DETAILED ANALYSIS OF THE
LOW SPEED COMPRESSOR CHARACTERISTICS OF THE T55 ENGINE IS BEING
PERFORMED IN AN EFFORT TO ENHANCE THE STARTING CAPABILITY OF THE
T55. HOWEVER, IT MUST AGAIN BE EMPHASIZED THAT THE PROCEDURES
DESCRIBED IN PARAGRAPH 9A ABOVE WILL GREATLY ENHANCE THE STARTING
CAPABILITY.
D. IN ADDITION TO THE ABOVE CORRECTIVE PROCEDURES, SOME OF THE
OTHER MANUAL CHANGES OF PARTICULAR INTEREST ARE DESCRIBED FOR
INFORMATIONAL PURPOSES.
(1) COMPRESSOR STATOR VANES HAVE FAILED FROM TWO
SEPARATE CAUSES. FIRST, COMPRESSOR STATOR VANE ASSEMBLY RETAINING
BOLTS HAVE OFTEN BEEN FOUND LOOSE. LOOSE BOLTS CAN ALLOW THE VANE
ASSEMBLY TO DEFLECT AND MAKE CONTACT WITH THE COMPRESSOR ROTOR AS
WELL AS ALLOW EXCESSIVE VIBRATORY STRESSES. AN UPCOMING MANUAL
CHANGE WILL INCREASE THE TORQUE ON THE 15 INCH POUND TORQUE STATOR
VANE RETAINING BOLTS TO 22 INCH POUND TORQUE. THE SECOND CAUSE IS
DUE TO EXCESSIVE VIBRATORY STRESSES ON THE FIRST STAGE STATOR VANE
WHICH LEADS TO VANE CRACKING AND POSSIBLE VANE SEPARATION. THE
CORRECTIVE ACTION IS A DEPOT MODIFICATION TO MODIFY THE STATOR VANE
ASSEMBLY AND INJECT ROOM TEMPERATURE VULCANIZING (RTV) BETWEEN THE
STATOR VANE ASSEMBLY AND THE COMPRESSOR HOUSING. A MANUAL CHANGE IS
FORTHCOMING TO PROVIDE INSTRUCTIONS TO INJECT THE RTV SHOULD
SUBSEQUENT REPLACEMENT OF THE FIRST STAGE STATOR VANE ASSEMBLY BE
REQUIRED.
(2) THERE HAVE BEEN SEVERAL REPORTS OF LEAKING OUTPUT
SHAFT SEALS. IT IS SUSPECTED THAT THE LEAKS AND SEAL FAILURES ARE
DUE TO CONTAMINATION OF THE SEALING AIR PASSAGES IN THE SEAL
RETAINER AND ITS HOUSING. A MANUAL CHANGE IS FORTHCOMING TO REQUIRE
CAREFUL INSPECTION AND CLEANING OF THE SEALING PASSAGES AT EACH
REPAIR OF THE SEAL TO REDUCE THE NUMBER OF LEAKS AND NEED FOR SEAL
REPLACEMENT.
(3) THE RELIABILITY OF THE CURRENT THERMOCOUPLE
HARNESSES HAS LED TO THE DEVELOPMENT AND QUALIFICATION OF A NEW
SERIES THAT SHOULD BE MUCH MORE DURABLE AND ACCURATE. WHILE
PROCUREMENT OF THE NEW SERIES IS TAKING PLACE, A MANUAL CHANGE IS
FORTHCOMING TO ALLOW THE CONTINUED OPERATION OF AN ENGINE WITH ONE
THERMOCOUPLE HARNESS DISCONNECTED. IF A RESISTANCE CHECK REVEALS A
DEFECTIVE THERMOCOUPLE HARNESS, THAT HARNESS MAY BE DISCONNECTED
FROM THE BUSBAR AND ITS LEADS TAPED WITH FIBERGLASS TAPE AND TO THE
BUSBAR IN ORDER TO REMOVE THE SIGNAL INPUT AND PREVENT DAMAGE DURING
OPERATION. AN ENGINE MAY BE OPERATED WITH ONLY ONE HARNESS
DISCONNECTED. IN ADDITION, THE RESISTANCE CHECK MAY BE PERFORMED *ON
WING' BY REMOVING THE TAILPIPE AND THE HARNESS LEADS FROM THE BUSBAR
INSTEAD OF REMOVING THE ENGINE/HARNESSES AS CURRENTLY DESCRIBED IN
THE MANUAL.
(4) RECENTLY MANUFACTURED AND OVERHAULED ENGINES
INCORPORATE HARDWARE CHANGES THAT IMPROVE ENGINE PERFORMANCE AND
TEMPERATURE MARGIN. AS A RESULT, THESE ENGINES CANNOT BE TRIMMED
DURING THE TURBINE ENGINE ANALYSIS CHECK (TEAC) TO MEET THE MINIMUM
PTIT (860C) WITHOUT EXCEEDING THE N1 SPEED LIMIT. AS A RESULT, A NEW
TEAC PROCEDURE WAS PUBLISHED THAT ALLOWS SETTING OF THESE ENGINES
NEAR THE N1 SPEED LIMIT DURING A BASELINE CHECK AND DETERMINING THE
MINUMUM PTIT FOR EACH ENGINE. IT SHOULD BE NOTED THAT A LOWER LIMIT
IS REQUIRED TO ASSURE THE INTEGRITY OF THE TEMPERATURE MEASUREMENT
SYSTEM SINCE THE THERMOCOUPLE PROBES TEND TO READ LOWER OVER TIME
DUE TO OXIDATION.
(5) THERE HAS BEEN ANOTHER INSTANCE OF THE OLDER
MATERIAL OIL LEVEL FLOAT (P/N 2-300-194-01) DISSOLVING AND
DISINTEGRATING IN THE OIL TANK OF AN ENGINE. AN IMPROVED OIL LEVEL
FLOAT (P/N 2-300-994-01) WAS RELEASED AND THE SUPPLY SYSTEM PURGED
OF THE OLD FLOATS BUT SOME ENGINES STILL HAVE THE OLD FLOAT
INSTALLED. THEREFORE, AT THE NEXT ACCESS TO THE OIL FLOAT DURING
MAINTENANCE OF THE INLET HOUSING, CHECK THE OIL FLOAT AND REPLACE IF
IT IS THE OLDER MATERIAL. THE OLDER MATERIAL FLOATS ARE MADE OF
MATERIAL THAT IS WHITE, WHEREAS THE IMPROVED FLOAT HAS A BROWNISH
COLOR.
(6) THERE HAS BEEN A FAILURE OF THE ACCESSORY GEARBOX
SCAVENGE PUMP WHICH HAS LED TO THE INCREASING OF TORQUE REQUIRED
DURING ASSEMBLY. THEREFORE, TASK 5-7 OF TM 55-2840-254-23-3 WILL BE
REVISED TO CHANGE THE TORQUE REQUIRED DURING ASSEMBLY AND
INSTALLATION OF PLUG (STEP 14) FROM 45 INCH-POUNDS TO 125-150 INCH
P0UNDS. THIS CHANGE WILL ONLY AFFECT SUBSEQUENT PERFORMANCE OF TASK
5-7.
10. SUPPLY/PARTS AND DISPOSITION - N/A.
11. SPECIAL TOOLS, JIGS AND FIXTURES REQUIRED - N/A.
12. APPLICATION -
A. CATEGORY OF MAINTENANCE - N/A.
B. TIME REQUIRED - N/A.
C. ESTIMATED COST IMPACT OF STOCK FUND ITEMS TO THE FIELD -
N/A.
D. TB/MWOS TO BE APPLIED PRIOR TO OR CONCURRENTLY WITH THIS
INSPECTION - N/A.
E. PUBLICATIONS WHICH REQUIRE CHANGE AS A RESULT OF THIS
INSPECTION - TM 55-2840-254-23 IS CURRENTLY BEING CHANGED TO REFLECT
THIS MESSAGE. A COPY OF THIS MESSAGE SHALL BE INSERTED IN THE TM AS
AUTHORITY TO IMPLEMENT THE CHANGE UNTIL THE PRINTED CHANGE IS
RECEIVED.
13. REFERENCES - TM 55-2840-254-23, AVIATION UNIT AND INTERMEDIATE
MAINTENANCE MANUAL, ENGINE, GAS TURBINE, MODEL T55-L-712, NSN
2840-01-030-4890, DTD 26 APR 83 WITH CHANGES.
14. RECORDING AND REPORTING REQUIREMENTS -
A. REPORTING COMPLIANCE SUSPENSE DATE (AIRCRAFT) - N/A.
B. TASK/INSPECTION REPORTING SUSPENSE DATE (AIRCRAFT) - N/A.
C. REPORTING COMPLIANCE SUSPENSE DATE (SPARES) - N/A.
D. TASK/INSPECTION REPORTING SUSPENSE DATE (SPARES) - N/A.
E. THE FOLLOWING FORMS ARE APPLICABLE AND ARE TO BE
COMPLETED IN ACCORDANCE WITH DA PAM 738-751, 15 JUN 92 - N/A.
15. WEIGHT AND BALANCE - N/A.
16. POINTS OF CONTACT -
A. TECHNICAL POINT OF CONTACT FOR THIS MESSAGE IS MR. GARY
KELLOGG, AMSAT-R-EPE, DSN 693-1157 OR COMMERCIAL 314/263-1157.
B. LOGISTICAL POINT OF CONTACT FOR THIS MESSAGE IS MR. NORM
HUSTON, SFAE-AV-CH-L, DSN 693-1415 OR COMMERCIAL 314/263-1415.
C. SAFETY POINT OF CONTACT FOR THIS MESSAGE IS MR. BRAD
MEYER, AMSAT-C-XS, DSN 693-2258/2085 OR COMMERCIAL
314/263-2258/2085.
D. FOREIGN MILITARY SALES (FMS) RECIPIENTS REQUIRING
CLARIFICATION OF ACTION ADVISED BY THIS MESSAGE SHOULD CONTACT MW4
JAY NANCE/MR. RON VAN REES, AMSAT-I-IA, DSN 693-3826/3659 OR
COMMERCIAL 314/263-3826/3659.
E. AFTER HOURS CONTACT ATCOM COMMAND OPERATIONS CENTER (COC)
DSN 693-2066/7 OR COMMERCIAL 314/263-2066/7.