Operational features of the DEC
Hot Start Preventer (HSP
Transient Droop Improvement
TGT limiting
NP overspeed protection
On the DEC, when does TGT limiting not prevent an overtemp?
Compressor stalls
Engine starts
Lockout
When does the DEC switch from the 10 minute TGT limit to the 2,5 minute limit?
When the opposite engine torque is less than 50%
Hoe does DEC TGT limiting work
The DEC commands the HMU to limit fuel flow to the engine when TGT reaches the dual engine 10 minute limiting value (879 degrees +/- 9)
What 3 things has to happen in order for the HSP to activate?
NG < 60%
NP < 50%
TGT >900
Before attempting a restart after the HSP has activated, the TGT must decrease below?
300 degrees or wait 25 seconds
Signals required for Transient Droop Improvement to work?
NR sensor mounted on the left accessory module
Collective position transducer mounted with two previous transducers on a modified bracket assembly in the mixing unit
Engine torque signal
Is NP overspeed protection still functional during DEC lockout operations?
Yes
When will the the EDECU switch from the 10 minute dual TGT limit to 2,5 minute s/e limit?
NP drops below 96%
Greater than 3% droop between reference NP and actual NP
Greater than 5% per second NP droop rate exists and NP less than or equal to NP reference speed
Two main differences between the DEC and EDECU (flight line supplement)
- The EDECU is not dependent on the other engines Q being less than 50% Fuel flow is regulated to hold a constant TGT. Transient increase above 903 is normal when pilot demands maximum power
- The EDECU has Discrete Application Selection Plug (DAS) installed allowing the engine to operate with 701D limiting values.
What is the TGT bias for the DEC?
112 degrees
Two power sources for the DEC/EDECU?
Primary: Engine alternator
Secondary: 400 Hz, 120 Vac Airframe Power
DEC functions (IN FLT HHOT)
- Isochronous NP Governing. DEC will maintain
Np reference - NP Reference from the cockpit, (INCR/DECR
from 96-100%) - Fault Indication. DEC code sent to corresponding ENG Q indicator and the FMS DEC status page.
- Load Sharing/Torque Matching. Increase Q
of low side to match up to 3% NP above
reference. - Transient Droop Compensation. 4-1
improvement to compensate for transient
rotor droop. Uses coll. Pos. transducer signal. - History Counter. Sends signals to History
Counter. - Hot Start Preventer. Tells ODV to shut off fuel
when 900°C is reached, Ng<60, Np<50. - Overspeed Protection. Triggered when Np
reaches 120±1%. - TGT Limiting. Limits fuel flow
when reaching appx. 879 Dual Eng,
903 (2½ min) when opp Q is < 50%.
