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• Lightoff
-Typically within
2-3 seconds
•EGT start limit
- 725°C
• Idle
- Indicated by
EGT and
fuel flow
reduction
- Typical start
time: 45 to
60 seconds
Idle
N2
Time
Lightoff
(2-3 sec)
35-45 seconds
to idle from lightoff
Idle
N1
Time
Lightoff
EGT
Time
Lightoff
460-550°C EGT
at idle
FF
Time
Fuel shutoff
open
650-800 pph
at idle
Peak EGT = 550-650°C Peak FF = 300-420 pph prior to lightoff
600-800 pph after lightoff
Noorrmaall Oppeerraattiioonn
127
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Low Speed Stall Characteristics
• Engine speed stagnates immediately after
lightoff
• EGT rises rapidly
• Not self-recovering
- Recovery requires FADEC or flight
crew intervention
Idle
N2
Time
Lightoff
Idle
N1
Time
Lightoff
EGT
Time
Lightoff
EGT continues
to rise
FF
Time
Fuel shutoff
open
N2 40% i n stall N1 10% i n stall
725°C EGT limit
Idle
N2
Time
Lightoff
Idle
N1
Time
Lightoff
EGT
Time
Lightoff
725°C EGT limit
FF
Time
Fuel shutoff
open
Stall
Stall
Stall
Stall High Sub-idle Stall
• Engine stalls just below idle
• EGT rises rapidly
• Not self-recovering
- Recovery requires FADEC or flight crew
intervention
Lightoff Stall
Noorrmaall Oppeerraattiioonn
Start Stall Results (LPT 1)
128
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Autostart Failure to Lightoff Logic
Ground
Lightoff detected when EGT increases
55°C above initial EGT
If no lightoff within 15 seconds (20
seconds cold engine)
• Fuel and ignition turned off
• Dry-motored for 30 seconds
In-flight
If no lightoff within 30 seconds
• Flight crew must turn fuel off
• Observe a 30 second windmill/dry
motor period between start attempts
Selected Abbnnoorrmaall Coonnddiittiioonnss
Second start attempted with both ignitors for 15 seconds
If no lightoff on second attempt
• Start is aborted
• Fuel and ignition turned off
• Dry-motor for 30 seconds to purge the system of fuel
• Flight deck advisory
129
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Autostart Hot Starts, Start Stalls, Overtemperature Logic
Ground
If a hot start, start stall, or overtemperature
is detected
• Fuel metering valve closes for 6 seconds,
then opens with 7% fuel decrement
• Start fuel flow schedule is reduced at a
total of 21% in three 7% decerements
In-flight
If a hot start, start stall, or
overtemperature is encountered
• The flight crew must abort the
start
• Observe a 30 second
windmill/dry period between
start attempts
If the abnormality occurs after the third increment
• Start is aborted
• Fuel and ignition off
• Flight deck advisory
Selected Abbnnoorrmaall Coonnddiittiioonnss
130
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Start
Starter air pressure
• 25 psi desirable (start valve open)
•Warmer, slower starts with lower
pressure
Note: the practical minimum
starter air pressure is that
required to motor the engine to
22% N2 for auto start
(programmed fuel on speed) or
20% N2 for manual start
(minimum N2 for fuel on)
Ignition selection is automatic
•Autostart: FADEC alternates A
and B igniters on every other start
•Manual start: both igniters are
used
Fan rotation
• No restriction on opposite fan rotation
(tailwind)
- Initial N1 indication slower with a tailwind
• If no N1 rotation detected by ~51% N2, an
ECAM start fault message (“No N1”) is
provided to crew
- Start must be aborted
Tailwinds
• Starts demonstrated with 53 knot tailwind
• For CFM56-5A and –5B high tailwinds do not
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CFFM556 Flight Operations Support(18)
