Commuter experiences minor autoplt problem, preoccupation with aircraft equipment problem leads to h...

Attributes
ACN	129473
Time
Date	198911
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sna
State Reference	CA
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sna
Operator	common carrier : air taxi
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Navigation In Use	Other
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 4400 flight time type : 1600
ASRS Report	129473
Person 2
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Originally assigned 5000 on a vector of 040 degree right downwind for sna 194 in and out of scattered layer. Advised first officer that we would 'call the airport in sight' after we descended below clouds. Autoplt was coupled to flight director. Descending approximately 2000 FPM through 6000 for 5000 when controller issued clearance to 3000, heading 020 degree. Autoplt was in the midst of capturing 5000 when I dialed 3000 into the altitude alerter/preset. As I did so, aircraft pitched down about 10 degree resulting in a slight negative g-load on the aircraft. Autoplt should have dropped out of altitude mode and maintained a pitch attitude. While the first officer and I were sorting out the autoplt problem and configuring and slowing for approach, controller asked if we were heading 020 degree. We had not altered course because of the autoplt malfunction. Further vectors northwest put us in position for a visual, but the controller sounded irate. I don't believe there was a separation problem. Next time: disconnect autoplt immediately if malfunction occurs. Fly the airplane, take care of business.

Original NASA ASRS Text

Title: COMMUTER EXPERIENCES MINOR AUTOPLT PROBLEM, PREOCCUPATION WITH ACFT EQUIPMENT PROBLEM LEADS TO HEADING DEVIATION.

Narrative: ORIGINALLY ASSIGNED 5000 ON A VECTOR OF 040 DEG RIGHT DOWNWIND FOR SNA 194 IN AND OUT OF SCATTERED LAYER. ADVISED F/O THAT WE WOULD 'CALL THE ARPT IN SIGHT' AFTER WE DESCENDED BELOW CLOUDS. AUTOPLT WAS COUPLED TO FLT DIRECTOR. DESCENDING APPROX 2000 FPM THROUGH 6000 FOR 5000 WHEN CTLR ISSUED CLRNC TO 3000, HDG 020 DEG. AUTOPLT WAS IN THE MIDST OF CAPTURING 5000 WHEN I DIALED 3000 INTO THE ALT ALERTER/PRESET. AS I DID SO, ACFT PITCHED DOWN ABOUT 10 DEG RESULTING IN A SLIGHT NEGATIVE G-LOAD ON THE ACFT. AUTOPLT SHOULD HAVE DROPPED OUT OF ALT MODE AND MAINTAINED A PITCH ATTITUDE. WHILE THE F/O AND I WERE SORTING OUT THE AUTOPLT PROBLEM AND CONFIGURING AND SLOWING FOR APCH, CTLR ASKED IF WE WERE HDG 020 DEG. WE HAD NOT ALTERED COURSE BECAUSE OF THE AUTOPLT MALFUNCTION. FURTHER VECTORS NW PUT US IN POSITION FOR A VISUAL, BUT THE CTLR SOUNDED IRATE. I DON'T BELIEVE THERE WAS A SEPARATION PROBLEM. NEXT TIME: DISCONNECT AUTOPLT IMMEDIATELY IF MALFUNCTION OCCURS. FLY THE AIRPLANE, TAKE CARE OF BUSINESS.

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.

Commuter experiences minor autoplt problem, preoccupation with aircraft equipment problem leads to heading deviation.