High Starting Fuel Flow 
Figure 104
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL //////////////////////// 
PREREQUISITES
FUEL FLOW IS NOT 
ENGINE OPERATION OR ENGINE MOTORING CAN BE NECESSARY
STABLE DURING START
YES 
NO
7 DO THE CIT SENSOR TEST 
(AMM 71-00-00/501, TEST 11). 
IS THE CIT SENSOR SERVICE-ABLE?
YES
Fuel Flow is Not Stable During Start 
Figure 105
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL //////////////////////// 
ENGINE WILL NOT  PREREQUISITES  
START ON ONE  115V AC ELECTRICAL POWER; ENGINE OPERATION MAY BE  
IGNITION SYSTEM  REQUIRED 
1
PERFORM IGNITION SYSTEM AUDIBLE CHECK ON FAILED SYSTEM (71-00-59, FIG. 109). 
IS SPARK HEARD? 
NO
11 REPLACE IGNITER PLUG 
(74-21-02). REPEAT AUDIBLE 
CHECK.
 IS SPARK HEARD? 
YES
(73-11-04) OR REPLACE ENGINE (71-00-02) AS REQUIRED. 
Engine will not Start on One Ignition System 
Figure 106
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL //////////////////////// 
INSTANTANEOUS  PREREQUISITES  
LIGHTUP (TORCHING)  NONE  
WITH START LEVER  
MOVEMENT/INTERNAL  
ENGINE FIRE AFTER  
SHUTDOWN 
YESYES
1 
VISUALLY EXAMINE ENGINE 
INLET AND EXHAUST AREAS FOR 
OBVIOUS SIGNS OF DAMAGE.
NO
IS DAMAGE FOUND?
YESNO 23 DO THE INSPECTION FOR ENGINE FIRE, HIGH NACELLE TEM-PERATURE, OR USE OF FIRE EXTINGUISHING AGENTS(AMM 72-00-00/601).
IS DAMAGE MORE THAN THE LIMITS FOUND? 
NO
25 REPAIR/REPLACE THE COMPO-NENTS AS NECESSARY. CONTINUE TO DO TROUBLESHOOTING AT BLOCK 5. 
YES
3 DO THE INSPECTION FOR 
ENGINE FIRE, HIGH NACELLE TEM-PERATURE, OR USE OF FIRE 
EXTINGUISHING AGENTS
(AMM 72-00-00/601).
IS DAMAGE MORE THAN THE LIMITS FOUND? 
SEE SHEET 2 
(BLOCK 7)
Instantaneous Lightup (Torching) with Start Lever Movement/Internal 
Engine Fire After Shutdown 
Figure 107 (Sheet 1)
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CFM56 ENGINES