Note that there maybe a folder named something like "dash8-q400_CVT_" generated inside the Community Mods Folder after installing the DHC8 and started the game for the first time. In case for any updates with this aircraft, delete the mentioned folder to make sure the changes to be applied.
For making the DHC8 really appear in AI traffic and report the aircraft model correctly during conversation with ATC, replace the [GENERAL] part the aircraft.cfg of the DHC8 (default path is "Dash8-Q400\SimObjects\AIRPLANES\Dash8", NOT the aircraft.cfg of the livery) to the following:
atc_type = "TT:ATCCOM.ATC_NAME DEHAVILLAND.0.text"
atc_model = "TT:ATCCOM.AC_MODEL DH8D.0.text"
editable = 1 ; 
performance = 70-78 Pax Regional Airliner\nLength: 107 ft\nWing Span: 93 ft\nHt: 24 ft-7 in\nWeight:32,836 lb Empty\nMax T\/O Weight:63,000 lb\nPower: 2 x 2,140 SHP P&W 150A Turboshafts\nMax Cruise: 414 Kts TAS\nStall Speed 120 Kts\nCeiling: 25,000 ft\nRange: 1,567 Naut Miles (max)with std fuel load. ; 
category = airplane ; 
icao_type_designator = "DH8D" ;
icao_manufacturer = "De Havilland Canada" ;
icao_model = "DHC-8" ;
icao_engine_type = "Turboprop/Turboshaft" ;
icao_engine_count = 2 ;
icao_wtc = "L" ;
icao_generic = 1 ;

You may also have interest for the following American Airlines liveries:

• A330-300
• A321

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