A C90 flight director computer malfunctioned causing a failure to capture the assigned altitude and ...

Attributes
ACN	654151
Time
Date	200504
Place
Locale Reference	navaid : ocf.vortac
State Reference	FL
Altitude	msl bound lower : 8000 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	general aviation : corporate
Make Model Name	King Air C90 E90
Operating Under FAR Part	Part 135
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : multi engine pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 3200 flight time type : 370
ASRS Report	654151
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment : altitude alert other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : overcame equipment problem flight crew : took evasive action flight crew : regained aircraft control
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

I received a crossing clearance to cross ocf at 11000 ft. Before reaching 11000 ft; I was cleared down to 9000 ft. I set 9000 ft in the altitude preselect and verified that the autoplt was armed. I noticed the plane not leveling off and took control away from the autoplt around 8800 ft (or at least I thought). Me pulling up was counteracted by a nose down trim input. I disconnected the electric trim switch with no change in control. Around 8500 ft; ATC told me that I received a clearance for 9000 ft. I replied that I thought I had a runaway trim; due to the fact that the trim continued trimming nose down after I had turned it off. They gave me a heading to steer away from traffic. I reached for the autoplt disconnect switch on the center console (this would be the second disconnect). Before actually pressing it; the autoplt let go. Total loss of altitude was maybe 800 ft. It was hard to say due to the porpoising of the airplane due to fighting the autoplt. Since this incident; the plane has been at the avionics shop. We ran some tests and found a problem in the computer of the flight director. It is shipped off for repair. I had a plane with 4 kids and 2 adults on their way to vacation. Needless to say; the kids were excited (not my kids). I don't think this was a factor; but maybe I could have caught it earlier; if there was less distraction.

Original NASA ASRS Text

Title: A C90 FLT DIRECTOR COMPUTER MALFUNCTIONED CAUSING A FAILURE TO CAPTURE THE ASSIGNED ALT AND AN 800 FT ALTDEV.

Narrative: I RECEIVED A XING CLRNC TO CROSS OCF AT 11000 FT. BEFORE REACHING 11000 FT; I WAS CLRED DOWN TO 9000 FT. I SET 9000 FT IN THE ALT PRESELECT AND VERIFIED THAT THE AUTOPLT WAS ARMED. I NOTICED THE PLANE NOT LEVELING OFF AND TOOK CTL AWAY FROM THE AUTOPLT AROUND 8800 FT (OR AT LEAST I THOUGHT). ME PULLING UP WAS COUNTERACTED BY A NOSE DOWN TRIM INPUT. I DISCONNECTED THE ELECTRIC TRIM SWITCH WITH NO CHANGE IN CTL. AROUND 8500 FT; ATC TOLD ME THAT I RECEIVED A CLRNC FOR 9000 FT. I REPLIED THAT I THOUGHT I HAD A RUNAWAY TRIM; DUE TO THE FACT THAT THE TRIM CONTINUED TRIMMING NOSE DOWN AFTER I HAD TURNED IT OFF. THEY GAVE ME A HDG TO STEER AWAY FROM TFC. I REACHED FOR THE AUTOPLT DISCONNECT SWITCH ON THE CTR CONSOLE (THIS WOULD BE THE SECOND DISCONNECT). BEFORE ACTUALLY PRESSING IT; THE AUTOPLT LET GO. TOTAL LOSS OF ALT WAS MAYBE 800 FT. IT WAS HARD TO SAY DUE TO THE PORPOISING OF THE AIRPLANE DUE TO FIGHTING THE AUTOPLT. SINCE THIS INCIDENT; THE PLANE HAS BEEN AT THE AVIONICS SHOP. WE RAN SOME TESTS AND FOUND A PROB IN THE COMPUTER OF THE FLT DIRECTOR. IT IS SHIPPED OFF FOR REPAIR. I HAD A PLANE WITH 4 KIDS AND 2 ADULTS ON THEIR WAY TO VACATION. NEEDLESS TO SAY; THE KIDS WERE EXCITED (NOT MY KIDS). I DON'T THINK THIS WAS A FACTOR; BUT MAYBE I COULD HAVE CAUGHT IT EARLIER; IF THERE WAS LESS DISTR.

Data retrieved from NASA's ASRS site as of January 2009 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.

A C90 flight director computer malfunctioned causing a failure to capture the assigned altitude and an 800 ft altitude deviation.