Flight crew overshoots altitude on descent, cites unreliable altitude capture on autoplt.

Attributes
ACN	112142
Time
Date	198905
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ape
State Reference	OH
Altitude	msl bound lower : 22700 msl bound upper : 23000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 210 flight time total : 13000 flight time type : 2000
ASRS Report	112142
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 216 flight time total : 2150 flight time type : 860
ASRS Report	112143
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Descending from FL290 to FL230, first officer flying on autoplt using speed select and vertical speed with 23000' armed. Speed 280 KIAS and 1000 FPM down. Captain removing approach plates for landing. Neither pilot touched flight guidance panel, but altitude arm lost. Aircraft descended through FL230 and altitude warning tone sounded at 22700'. Captain turned off autoplt and rapidly climbed back to 23000'. Total deviation, 350'. No mention of deviation by ATC. This FGS does not work well. I have flown and am rated on the large transport and large transport all with digital FGS. The type 'a' system is not user friendly. It contains numerous means of wiping out an altitude arm, which would not affect the systems on the other aircraft. Also, due to cheap/inferior wiring, this system is loaded with electrical problems--electrical impulses causing mode changed not commanded by the pilot. Many aircraft systems are affected by these extraneous electrical impulses. We were told in 1983 that these problems would be corrected--especially on the flight guidance computer. Nothing has been corrected in 6 yrs. Please refer to an air carrier 'a,' type 'a' operating manual and read the lengthy pink bulletins concerning flight guidance computer anomalies. Where the heck is the public safety interest represented by the FAA? NTSB? NASA? I'm tired of filling out NASA reports on this airplane...help!

Original NASA ASRS Text

Title: FLT CREW OVERSHOOTS ALT ON DESCENT, CITES UNRELIABLE ALT CAPTURE ON AUTOPLT.

Narrative: DSNDING FROM FL290 TO FL230, F/O FLYING ON AUTOPLT USING SPD SELECT AND VERT SPD WITH 23000' ARMED. SPD 280 KIAS AND 1000 FPM DOWN. CAPT REMOVING APCH PLATES FOR LNDG. NEITHER PLT TOUCHED FLT GUIDANCE PANEL, BUT ALT ARM LOST. ACFT DSNDED THROUGH FL230 AND ALT WARNING TONE SOUNDED AT 22700'. CAPT TURNED OFF AUTOPLT AND RAPIDLY CLBED BACK TO 23000'. TOTAL DEVIATION, 350'. NO MENTION OF DEVIATION BY ATC. THIS FGS DOES NOT WORK WELL. I HAVE FLOWN AND AM RATED ON THE LGT AND LGT ALL WITH DIGITAL FGS. THE TYPE 'A' SYS IS NOT USER FRIENDLY. IT CONTAINS NUMEROUS MEANS OF WIPING OUT AN ALT ARM, WHICH WOULD NOT AFFECT THE SYSTEMS ON THE OTHER ACFT. ALSO, DUE TO CHEAP/INFERIOR WIRING, THIS SYS IS LOADED WITH ELECTRICAL PROBS--ELECTRICAL IMPULSES CAUSING MODE CHANGED NOT COMMANDED BY THE PLT. MANY ACFT SYSTEMS ARE AFFECTED BY THESE EXTRANEOUS ELECTRICAL IMPULSES. WE WERE TOLD IN 1983 THAT THESE PROBS WOULD BE CORRECTED--ESPECIALLY ON THE FLT GUIDANCE COMPUTER. NOTHING HAS BEEN CORRECTED IN 6 YRS. PLEASE REFER TO AN ACR 'A,' TYPE 'A' OPERATING MANUAL AND READ THE LENGTHY PINK BULLETINS CONCERNING FLT GUIDANCE COMPUTER ANOMALIES. WHERE THE HECK IS THE PUBLIC SAFETY INTEREST REPRESENTED BY THE FAA? NTSB? NASA? I'M TIRED OF FILLING OUT NASA RPTS ON THIS AIRPLANE...HELP!

Data retrieved from NASA's ASRS site as of August 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.