FA50 CAPT ACKNOWLEDGES ZAU DSCNT XING CLRNC AGAINST FO WISHES. A 5000 FPM DSCNT CAUSES A 200 FT OVERSHOOT.

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ZAU REQUESTED US TO MAKE BEARZ AT 11000 FT MSL AFTER HOLDING US AT A HIGHER ALT. I ADVISED THE CAPT THAT IT WOULD BE DIFFICULT TO ACCOMPLISH; YET HE RESPONDED TO THE CTLR 'BEARZ AT 11000 FT.' ORD CTR THEN CAME BACK AND SAID TO DO THE BEST YOU CAN TO TRY AND MAKE BEARZ AT 11000 FT. THE DSCNT REQUIRED IN EXCESS OF 5000 FPM RAT OF DSCNT TO ACCOMPLISH. I INITIATED THE DSCNT TOWARDS 11000 FT. AS I PASSED THROUGH 12000 FT MSL; I ADJUSTED THE AUTOPLT'S VSI RATE OF DSCNT TO ACCOMPLISH A LEVELOFF IN A SAFE FASHION. UNFORTUNATELY; DUE TO THE HIGH RATE OF DSCNT; THE AUTOPLT HAD ALREADY ENTERED INTO THE CAPTURE LOGIC FOR 11000 FT. DUE TO TRYING TO 'ADJUST' THE VSI CTLR WHEN THE AUTOPLT HAD ALREADY ENTERED INTO THE 'CAPTURE' MODE; IT CAUSED THE AUTOPLT TO REVERT TO RAW PITCH MODE. I CAUGHT IT IMMEDIATELY; BUT DUE TO THE CONTINUED HIGH RATE OF DSCNT AND DISCONNECTING OF THE AUTOPLT; I OVERSHOT MY ALT BY 200 FT. THE ACFT BOTTOMED OUT AT 10800 FT MSL BEFORE CLBING BACK TO 11000 FT MSL. THE ORD CTLR CONFIRMED THAT WE WERE; IN FACT; LEVEL AT 11000 FT AT BEARZ. WE; IN FACT WERE; WHEN HE MADE THE QUERY. I'M NOT SURE IF HIS QUERY WAS DUE TO AN ALT WARNING THAT HE RECEIVED WHEN WE MOMENTARILY BOTTOMED OUT AT 10800 FT MSL. REGARDLESS OF THE REASON FOR THE QUERY; AN IMPORTANT LESSON WAS LEARNED. ACCEPTING A RATE OF DSCNT IN EXCESS OF 4500 FPM IS NOT PRUDENT. IN OUR CASE; 5000 FPM WAS REQUIRED TO MAKE THE ALT RESTR. IN THE FUTURE; I WILL BE MORE FORCEFUL WITH THE CAPT AND MORE EXPLICIT WITH ATC WITH DSCNT PARAMETER RESTRAINTS. ADDITIONALLY; I WILL NOT ACCEPT DSCNTS THAT REQUIRE IN EXCESS OF 4000 FPM UNLESS AN EMER OR CRITICAL SIT EXISTS. IT GOES BACK TO THE OLD ADAGE OF A 'FAILURE TO PLAN ON YOUR PART; SHOULD NOT CONSTITUTE A CRISIS ON MY PART.' DON['T LET ATC (OR THE CAPT) PAINT YOU INTO A CORNER. ADDITIONALLY; DURING HIGH RATES OF DSCNT; BE AWARE THAT MOST AUTOPLTS WILL ENTER INTO THE 'CAPTURE' MODE MUCH EARLIER THAN YOU'RE ACCUSTOMED TO. BE PREPARED FOR THIS.