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Old 8th Sep 2019, 11:42
  #35 (permalink)  
H Peacock
 
Join Date: Sep 2004
Location: Yorkshire
Posts: 607
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I never understood the switch on Tucano that went from ground idle to ‘flight mode’ or similar, but was overridden by throttle being advanced anyway...why was that required? Anyone recall?
The switch was for you to tell the EEC what rpm you wanted on the ground; 72% was somewhat quieter than the normal 100%. Provided you'd blipped the switch to 70% pre-start then the engine would start and sit at 72% (the setting of the underspeed governor) When you put the Air Con on it was pushed up to 80% for a tad more bleed air. Runway checks got you to select 100% to re-datum the underspeed governor, but if you forgot then the EEC would respond to a forward throttle movement and do it for you. The latter did cause a slight EGT spike as the increased fuel flow (throttle) exceeded that demanded by the underspend governor. You couldn't therefore try to get airborne before you had 100% rpm. The transition form 72 (or 80) to 100% was fairly rapid anyway.

Inflight the switch did nothing, then after landing you blipped it back to 70 to quieten things down again.
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