DEFDARS  Digital Expandable Flight Data Acquisition and 
Recording.System 
DEFL  Deflection 
DEG  Degree 
DEL  Delete 
Demand Mode  An.ACARS.mode.of.operation.in.which. 
communications.may.be.initiated.by.the.ground. 
processor.or.the.airborne.system. 
DEP  (.1.).Departure.. 
(.2.).Design.Eye.Position..The.position.at.each. 
pilot’s.station.from.which.a.seated.pilot.achieves. 
the.optimum.combination.of.outside.visibility.and. 
instrument.scan. 
DER  Designated.Engineering.Representative:. 
Designation.of.authority.by.the.FAA.authorized. 
under.FAR.Part.183,.Subpart.B. 
DES  Descent 
DESCR  Description 
Desensitization  TCAS.sensitivity.level.(threat.volume).reduction 
DES  Descent:.An.autopilot.Flight.director.mode. 
DEST  Destination 
DEV  Deviation 
DF  Definition File 
DFA  Direction.Finding.Antenna 
DFCS  Digital.Flight.Control.System 
DFDAF  Digital Flight Data Acquisition Function 
DFDAMU  Digital Flight Data Acquisition Management Unit 
DFDAU  Digital Flight Data Acquisition Unit. The DFDAU 
samples, conditions and digitizes the flight data. 
DFDR  Digital.Flight.Data.Recorder 
DFDU  Digital.Flight.Data.Unit 
DFIDU  Dual.Function.Interactive.Display.Unit 
DFIU  Digital.Flight.Instrument.Unit 
DFS  Digital Frequency Select 

DFU  Digital.Function.Unit 
DG  Directional.Gyro:.Mode.of.AHS.operation.that. 
provides heading data without the benefit of a flux 
(AHRS).or.normal.alignment.(IRS). 
DGAC  Direction.Generale.de.l’Avaiation.Civile.(France’s. 
Civil.Aviation.Agency). 
DGNSS  Differential.Global.Navigation.Satellite.System 
DGPS  Differential.Global.Positioning.System. 
DH  ( 1 ) Dataflash Header . 
( 2 ) Decision Height: Specified height in the 
precision.approach.at.which.a.missed.approach. 
must be initiated if the required visual reference to 
continue.the.approach.has.not.been.established.