▁power ed ▁by ▁tur b op rop ▁engines . ▁ ▁In ▁response ▁to ▁air lines ▁often ▁wanting ▁to ▁replace ▁their ▁early ▁production ▁A TR ▁models ▁with ▁the ▁latest ▁generation ▁A TR ▁series , ▁as ▁well ▁as ▁to ▁answer ▁demand ▁from ▁cargo ▁operators ▁for ▁the ▁type , ▁A TR ▁has ▁operated ▁two ▁separate ▁dedicated ▁fre ighter ▁conversion ▁program mes , ▁known ▁as ▁the ▁Bul k ▁Fre ighter ▁( t ube ▁version ) ▁and ▁the ▁U LD ▁Fre ighter . ▁Both ▁convers ions ▁involve ▁complete ▁stri pping ▁of ▁furn ish ings ▁along ▁with ▁the ▁addition ▁of ▁floor ▁strength ening , ▁new ▁window ▁pl ugs ▁and ▁ 9 g ▁rest ra ining ▁n ets , ▁six ▁additional ▁longitud inal ▁tracks ▁for ▁added ▁flex ibility , ▁and ▁an ▁E - Class ▁cabin ; ▁the ▁U LD ▁model ▁can ▁accommod ate ▁standard ▁U LD - pack aged ▁cargo , ▁such ▁as ▁L D 3 ▁containers ▁or ▁ ▁pal lets , ▁which ▁were ▁loaded ▁via ▁a ▁large ▁cargo ▁door ▁located ▁on ▁the ▁port ▁forward ▁side . ▁Und ert aken ▁by ▁a ▁range ▁of ▁companies , ▁such ▁as ▁Al enia ▁subs idi ary ▁Aer on av ali , ▁Texas - based ▁M 7 ▁A eros pace ; ▁French ▁fir ms ▁Ind ra éro ▁Sir en ▁and ▁A ero con se il , ▁Canadian ▁In fin ion ▁Cert ification ▁Engineering , ▁and ▁Spanish ▁company ▁Ar ro dis a , ▁by ▁October ▁ 2 0 1 2 , ▁in ▁excess ▁of ▁one - fif th ▁of ▁all ▁first - gener ation ▁A