APCH CTLR QUESTIONS ALT AND RATE OF DSCNT OF DC8 FREIGHTER AS ACFT IS SLOWED FOR FLAP EXTENSION. POTENTIAL CONFLICT WITH ACFT Y WAS A POSSIBILITY WITH NO FURTHER RATE OF DSCNT. ACFT X HAD NO TCASII AND WAS NOT AWARE OF OTHER TFC IN AREA.

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ATC ISSUED DSCNT FROM 6000 FT TO 4000 FT MSL; WITH NO TA. PLT INITIATED A SLOW/MOMENTARY DELAY DURING DSCNT FOR ACFT CONFIGN TO PREVENT OVERSPD DURING FLAP EXTENSION. ATC QUESTIONED ACFT DSCNT IMPLYING 'WHY ARE YOU CLBING; YOU WERE CLRED TO 4000 FT.' ACFT WAS NOT CLBING; WE HAD DSNDED OUT OF 6000 FT AND MOMENTARILY SLOWED DSCNT AT 5800 FT FOR SPD REDUCTION. ATC WAS INFORMED THAT WE WERE CONFIGURING AND ATC'S RESPONSE SUGGESTED THAT ATC HAD ADDITIONAL TFC. REMAINDER OF DSCNT WAS EXPEDITED TO 4000 FT. CONTRIBUTING FACTORS WAS ATC'S FAILURE TO GIVE TFC INFO AND THE NECESSITY FOR ACFT TO EXPEDITE OUR DSCNT FROM 6000-4000 FT. (NORMALLY A REQUIRED CALL.) ATC ALSO SEEMED UNFAMILIAR WITH THE ACFT CHARACTERISTICS OF THE DC8; REQUIRING AN ALMOST LEVEL PITCH ATTITUDE TO REDUCE SPD TO ALLOW FLAP EXTENSION WITHOUT AN OVERSPD. EVEN WITH ATC FAILING TO ISSUE TFC INFO; IF CARGO CARRIERS WERE REQUIRED TO HAVE TCASII THE CREW MAY HAVE POSSIBLY SEEN ANY POTENTIAL TFC AND EXPEDITED DSCNT. SUPPLEMENTAL INFO FROM ACN 362611: WE MOMENTARILY LEVELED OFF AT 5800 FT WHILE THE FLAPS MOVED TO THEIR INITIAL POS. AT THIS POINT; THE SOCAL APCH CTLR SAID; 'WHY ARE YOU CLBING? YOU ARE CLRED TO 4000 FT.' HE STATED THAT 'YOU NEED TO DSND FOR TFC.' THIS WAS THE FIRST TIME HE HAD MENTIONED A TFC CONFLICT. I LOOKED OUT THE L WINDOW AND SAW POS LIGHTS ABOVE AND TO THE L OF US. WE CONTINUED DSCNT AND LANDED UNEVENTFULLY. I EXPLAINED TO THE SOCAL CTLR THAT WE HAD EXTENDED THE FLAPS AND MAY HAVE CLBED A MAX OF 100 FT DUE TO BALLOONING OF THE ACFT DURING FLAP EXTENSION.