C402 pilot experiences track and altitude deviations during ILS approach to test possible malfunctio...

Attributes
ACN	968469
Time
Date	201109
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.TRACON
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	Cessna 402/402C/B379 Businessliner/Utiliner
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine Flight Crew Instrument Flight Crew Flight Instructor Flight Crew Flight Engineer
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 13000 Flight Crew Type 1200
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

On a flight to reposition aircraft to avionics shop to test possible malfunctioning autopilot. Being vectored by approach. Cleared for approach at 2000 with intercept heading localizer tuned and identified. Turned on autopilot to intercept and fly approach. The aircraft began a steep descent to 1600 feet and continued through the centerline of approach per ATC. The in-cockpit indications never showed a needle movement. Pilot disconnected autopilot and hand flew the aircraft back to the assigned altitude and a new heading after approach controller canceled approach clearance. Flight returned to the departure airport. No further use of autopilot for the remainder of trip. Aircraft flown the next day under VFR conditions to the avionics shop for inspection and repair.

Original NASA ASRS Text

Title: C402 pilot experiences track and altitude deviations during ILS approach to test possible malfunctioning autopilot. Malfunctioning is confirmed and the aircraft is flown under VMC for repair the next day.

Narrative: On a flight to reposition aircraft to avionics shop to test possible malfunctioning autopilot. Being vectored by Approach. Cleared for approach at 2000 with intercept heading localizer tuned and identified. Turned on autopilot to intercept and fly approach. The aircraft began a steep descent to 1600 feet and continued through the centerline of approach per ATC. The in-cockpit indications never showed a needle movement. Pilot disconnected autopilot and hand flew the aircraft back to the assigned altitude and a new heading after Approach Controller canceled approach clearance. Flight returned to the departure airport. No further use of autopilot for the remainder of trip. Aircraft flown the next day under VFR conditions to the avionics shop for inspection and repair.

Data retrieved from NASA's ASRS site as of April 2012 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.