F900 CREW ON TEST FLT AND ON IFR FLT PLAN WITH ZMP LEAVE ASSIGNED ALT WITHOUT ATC APPROVAL.

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THE PURPOSE OF THIS FLT WAS TO PERFORM A REQUIRED FUNCTIONAL TEST OF NEWLY INSTALLED EGPWS; A NEWLY INSTALLED MAGNASTAR FLT PHONE SYS AND TO PERFORM A POST MAINT SYS CHK OF THE ACFT THAT HAD JUST CAME OUT OF A MAJO INSPECTION. DUE TO UNEXPECTED PROBS; THE MAINT FACILITY DID NOT HAVE THE ACFT READY TO FLY UNTIL XA00; 7 HRS AFTER OUR ARR. BY THE TIME WE DEPARTED FOR THE FLT WE HAD BEEN ON DUTY FOR A LITTLE OVER 8 HRS. WE WERE HANDED OFF TO ZMP AND EVENTUALLY CLRED TO OUR INITIAL CRUISE ALT OF 14000 FT MSL. THE SIC CONTACTED MINNEAPOLIS TO BRIEF THEM OF OUR INTENTIONS; THAT IS; AFTER PASSING IWD WE WERE GOING TO NEED TO DSND TO 2000 FT MSL OVER LAKE SUPERIOR IN ORDER TO PERFORM THE OVERFLY OF CUYAHOGA PEAK (TF3) REQUIRED FOR OUR EGPWS FUNCTIONAL TEST. CTLR #1 HANDED US OFF TO THE NEXT SECTOR ADVISING US TO WAIT ABOUT 5 MINS BEFORE MAKING OUR REQUEST. WE CONTACTED ZMP ON THE NEW FREQ AND THE NEW CTLR (CTLR #2) IMMEDIATELY ASKED US OUR INTENTIONS. WE REITERATED OUR INTENT TO DSND TO 2000 FT OVER LAKE SUPERIOR WITH CTLR #2. CTLR #2 INFORMED US THAT HE COULD NOT CLR US TO 2000 FT OVER THE LAKE ON AN IFR FLT PLAN. WE TOLD HIM THAT IN THAT CASE WE WOULD CANCEL IFR AT IRONWOOD AND THEN CONTACT HIM AFTER COMPLETION OF THE TEST FOR AN IFR CLRNC BACK TO ATW. HE ASKED WHO WAS GOING TO CANCEL THE IFR; HIM OR US; AND WE SAID WE WOULD. WE BELIEVE HE RESPONDED 'ROGER.' AS WE APCHED IWD; WE REQUESTED A LOWER ALT IN ORDER TO BEGIN OUR WAY DOWN TO BE AT OUR PLANNED 2000 FT ALT IN TIME FOR OUR PASS OVER CUYAHOGA PEAK. CTLR #2 WAS VERY BUSY; IT SEEMED; AND HE BROADCAST THAT HE WAS GETTING SEVERAL CALLS WITH THE SAME REQUEST AND WAS GOING TO HAVE TO TAKE THEM ONE AT A TIME. WE ARE NOT SURE WHAT HIS EXACT RESPONSE WAS AT THAT TIME TO OUR REQUEST FOR A LOWER ALT. THERE WERE SEVERAL ACFT CALLING AND IT IS POSSIBLE HE WAS BLOCKED OR STEPPED ON. ENRTE TO IWD WE SET UP OUR FMS FOR A VNAV DSCNT TO REACH OUR FIRST EGPWS TEST WAYPOINT AT 2000 FT. WE SET THE ASEL TO 2000 FT AS WE WERE EXPECTING A QUICK CLRNC AND WE WERE RAPIDLY APCHING OUR FMS CALCULATED TOP OF DSCNT POINT. REALIZING THAT WE WERE GOING TO MAKE A HURRIED DSCNT AND THAT THE CTLR WAS OVER TASKED; WE CALLED AGAIN AND TOLD HIM WE WERE CANCELING IFR. WE WANTED TO EXPEDITE OUR DSCNT AND RELIEVE THE CTLR BY GOING VFR. THE CTLR RESPONDED SAYING AGAIN THAT SEVERAL ACFT WERE REQUESTING CANCELLATIONS AT THE SAME TIME AND THE SIC THOUGHT HE SAID THAT HE WAS UNABLE TO RELEASE US (OR PERHAPS ANOTHER ACFT HE WAS TALKING TO) AT THE TIME; THE PIC THOUGHT HE SAID; IFR CANCELED. THROUGHOUT THE FLT OUR MAINT CREW MEMBERS WOULD PERIODICALLY ENGAGE US IN CONVERSATION ABOUT VARIOUS ASPECTS OF THE FUNCTIONAL CHKS THEY WERE PERFORMING. COINCIDENT WITH THE CURRENT COM PROB WE WERE HAVING WITH ATC; ONE OF THE TECHNICIANS; UNAWARE OF THE SIT; ASKED US A QUESTION. SIMULTANEOUSLY; THE VNAV ENGAGED AND BEGAN OUR DSCNT FOR 2000 FT MSL. THE PF; DISTR BY THE MAINT CREW; WAS NOT AWARE THAT WE WERE NOT CLRED YET TO DSND; HE THOUGHT HE HEARD THE CTLR SAY 'IFR CANCELED.' MEANWHILE; THE SIC; ALONG WITH BEING DISTR MOMENTARILY BY THE MAINT CREW'S QUESTIONS; WAS ALSO BUSY TRYING TO GET A CONFIRMATION FROM THE CTLR THAT WE HAD CANCELED IFR. WHEN THE SIC REALIZED THAT THE ACFT WAS DSNDING; HE ADVISED THE PIC THAT WE HAD BETTER GET BACK UP TO 14000 FT. THE PIC IMMEDIATELY REALIZED OUR ERROR AND BEGAN RETURNING TO OUR CLRNC ALT OF 14000 FT. BECAUSE WE HAD PAX MOVING ABOUT THE CABIN; IT WAS NECESSARY TO MAKE A SMOOTH LEVELOFF AND TRANSITION RATHER THAN AN ABRUPT PITCH UP MANEUVER TO RETURN TO THE ASSIGNED ALT WITHOUT UPSETTING THE PAX AND CAUSING THEM POSSIBLE INJURY. AS WE BEGAN OUR CLB TO 14000 FT; WE GOT A TCASII TA SHOWING A TARGET 3 MI AT OUR 7-8 O'CLOCK POS INDICATING 300 FT BELOW OUR ALT. AT THE SAME TIME THE CTLR ASKED FOR OUR ALT AND THE SIC RESPONDED THAT WE WERE AT 13500 FT AND RETURNING TO 14000 FT. WE WERE BACK AT 14000 FT IN ABOUT 15 SECONDS. THE CTLR ASKED WHAT WE WERE DOING DOWN THERE AND; AS WE WERE TRYING TO FIGURE THAT OUR OURSELVES; THE SIC TOLD HIM THAT WE HAD AN EQUIP MALFUNCTION (BECAUSE AT FIRST THAT IS WHAT THE SIC THOUGHT IT WAS) THAT WE DIDN'T CATCH IN TIME; AND THAT WE WERE SORRY. IT WAS IN HINDSIGHT; AN AUTOMATION SURPRISE PERHAPS CAUSED BY PREMATURELY SETTING THE ASEL TO 2000 FT. THE CTLR SAID THERE WAS PROBABLY GOING TO BE SOME PAPERWORK INVOLVED BECAUSE THERE WAS OTHER IFR TFC IN THE AREA AND TO STAND BY FOR A PHONE NUMBER.