Narrative:

While level at high speed cruise (FL270) we were given descent clearance to a lower altitude by ZAU. The autoplt/flight director in our new airplane is the SP2-8000 digital efcs. Problems have been noted with it before that the manufacturer seems reluctant to address. Specifically, we were 10-20 KIAS below the barber pole when the altitude select and vertical speed modes of the autoplt/flight director were selected. When the pitch wheel was rolled forward to program the required descent rate, the autoplt pitches up to maintain speed below the barber pole. This happens at even moderately high speed. An altitude of 700 ft above the initial cruise altitude was reached before the descent was initiated. By then, the IAS was some 50 KTS below the barber pole. This is an unsafe autoplt system and I urge that it be examined closely by the certification auths. Calls to other flight departments have disclosed similar problems and calls to the manufacturer have gone unresolved. Callback conversation with reporter revealed the following information: reporter stated that the autoplt was a brand new designed honeywell spz 8000 difcs (digial efcs) on a brand new cessna 650 citation III aircraft. He related that there was no way to just go to a descent mode only with this autoplt. There is only altitude hold or flight level change (flight crew). When preselecting a lower altitude and rate of descent, the aircraft will be pitched up first if the speed is within 10 or less KTS of the maximum speed of the barber pole (mach speed indicator). He stated that there is no other way to program the autoplt for an altitude change, such as, vertical speed mode only which would not connect the speed control. He said that the descent can only be made by first slowing up to 40 or 50 KTS less than the maximum speed and then keeping the speed less with throttle control. He went on to say that he heard that this was built into the autoplt software to meet FAA certification requirements to prevent inadvertently over- speeding the cessna III aircraft. With regard to training received on this aircraft, the reporter stated that the simulator did not have this characteristic or problem so was not trained in the exact autoplt design that is in the aircraft. He will raise the subject with other pilots and instructors on his upcoming recurrent training. He did talk to some honeywell pilot and representatives at the airport he is based at and they believe that the autoplt is working as designed, certified and ok.

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Original NASA ASRS Text

Title: ACFT EQUIP DESIGN PROB NOT BEING ADDRESSED BY THE MANUFACTURER.

Narrative: WHILE LEVEL AT HIGH SPD CRUISE (FL270) WE WERE GIVEN DSCNT CLRNC TO A LOWER ALT BY ZAU. THE AUTOPLT/FLT DIRECTOR IN OUR NEW AIRPLANE IS THE SP2-8000 DIGITAL EFCS. PROBS HAVE BEEN NOTED WITH IT BEFORE THAT THE MANUFACTURER SEEMS RELUCTANT TO ADDRESS. SPECIFICALLY, WE WERE 10-20 KIAS BELOW THE BARBER POLE WHEN THE ALT SELECT AND VERT SPD MODES OF THE AUTOPLT/FLT DIRECTOR WERE SELECTED. WHEN THE PITCH WHEEL WAS ROLLED FORWARD TO PROGRAM THE REQUIRED DSCNT RATE, THE AUTOPLT PITCHES UP TO MAINTAIN SPD BELOW THE BARBER POLE. THIS HAPPENS AT EVEN MODERATELY HIGH SPD. AN ALT OF 700 FT ABOVE THE INITIAL CRUISE ALT WAS REACHED BEFORE THE DSCNT WAS INITIATED. BY THEN, THE IAS WAS SOME 50 KTS BELOW THE BARBER POLE. THIS IS AN UNSAFE AUTOPLT SYS AND I URGE THAT IT BE EXAMINED CLOSELY BY THE CERTIFICATION AUTHS. CALLS TO OTHER FLT DEPTS HAVE DISCLOSED SIMILAR PROBS AND CALLS TO THE MANUFACTURER HAVE GONE UNRESOLVED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE AUTOPLT WAS A BRAND NEW DESIGNED HONEYWELL SPZ 8000 DIFCS (DIGIAL EFCS) ON A BRAND NEW CESSNA 650 CITATION III ACFT. HE RELATED THAT THERE WAS NO WAY TO JUST GO TO A DSCNT MODE ONLY WITH THIS AUTOPLT. THERE IS ONLY ALT HOLD OR FLT LEVEL CHANGE (FLC). WHEN PRESELECTING A LOWER ALT AND RATE OF DSCNT, THE ACFT WILL BE PITCHED UP FIRST IF THE SPD IS WITHIN 10 OR LESS KTS OF THE MAX SPD OF THE BARBER POLE (MACH SPD INDICATOR). HE STATED THAT THERE IS NO OTHER WAY TO PROGRAM THE AUTOPLT FOR AN ALT CHANGE, SUCH AS, VERT SPD MODE ONLY WHICH WOULD NOT CONNECT THE SPD CTL. HE SAID THAT THE DSCNT CAN ONLY BE MADE BY FIRST SLOWING UP TO 40 OR 50 KTS LESS THAN THE MAX SPD AND THEN KEEPING THE SPD LESS WITH THROTTLE CTL. HE WENT ON TO SAY THAT HE HEARD THAT THIS WAS BUILT INTO THE AUTOPLT SOFTWARE TO MEET FAA CERTIFICATION REQUIREMENTS TO PREVENT INADVERTENTLY OVER- SPDING THE CESSNA III ACFT. WITH REGARD TO TRAINING RECEIVED ON THIS ACFT, THE RPTR STATED THAT THE SIMULATOR DID NOT HAVE THIS CHARACTERISTIC OR PROB SO WAS NOT TRAINED IN THE EXACT AUTOPLT DESIGN THAT IS IN THE ACFT. HE WILL RAISE THE SUBJECT WITH OTHER PLTS AND INSTRUCTORS ON HIS UPCOMING RECURRENT TRAINING. HE DID TALK TO SOME HONEYWELL PLT AND REPRESENTATIVES AT THE ARPT HE IS BASED AT AND THEY BELIEVE THAT THE AUTOPLT IS WORKING AS DESIGNED, CERTIFIED AND OK.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.