FLC OF AN LTT DSNDED BELOW ASSIGNED ALT WHEN LOSING THE PWR OF ONE ENG DUE TO LOW OIL PRESSURE. WITH ONE OF THE TWO ENGS AT FLT IDLE; THE CREW COULD NOT HOLD ALT AND THEY WERE DELAYED IN CONTACTING ATC DUE TO FREQ CONGESTION. EMER WAS NOT DECLARED!

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AT FL230 WE NOTICED OUR R OIL PRESSURE GAUGE WAS IN THE RED (55 PSI). AS PER THE CHKLIST; WE BROUGHT THE R ENG TO IDLE TO TRY AND DISCOVER THE PROB. OUR SINGLE ENG CEILING IS 17000 FT SO WE WERE UNABLE TO MAINTAIN FL230. I WAS WORKING THE RADIOS AND REQUESTED 17000 FT FROM ZDV. AFTER THE THIRD CALL; DEN REPLIED; 'CALL ZDV ON 128.85.' AFTER SWITCHING FREQS I HAD TO WAIT BEFORE I COULD REQUEST LOWER BECAUSE THE CTLR WAS TOO BUSY. ONCE I HAD THE CTLR'S ATTN; I REQUESTED 17000 FT. THE CTLR REPLIED 'SAY YOUR ALT.' I TOLD HER WE WERE DSNDING THROUGH 22300 FT BECAUSE WE HAD AN OIL PRESSURE PROB AND WERE UNABLE TO MAINTAIN 23000 FT AND AGAIN REQUESTED 17000 FT. SHE GAVE US 17000 FT. WE THEN RECEIVED A CLRNC FOR A PRECAUTIONARY LNDG AT RAP. TECHNICALLY WE BUSTED OUR ALT AT FL230. HOWEVER; IF THE 2 CTLRS WOULD NOT HAVE BEEN SO BUSY WITH OTHER TFC; WE COULD HAVE GOTTEN AN AMENDED ALT AND AVOIDED THE WHOLE PROB. THE CTR CTLRS ARE COVERING TOO MUCH TERRITORY AND TOO MANY FREQS. THEY ARE NOT AVAILABLE IF YOU NEED TO GET A HOLD OF THEM IN A HURRY.