Sb-20 captain reported receiving a GPWS obstacle warning while deviating from cleared track and alti...

Attributes
ACN	1241509
Time
Date	201502
Local Time Of Day	1801-2400
Place
Locale Reference	CLT.TRACON
State Reference	NC
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Make Model Name	Saab 2000
Operating Under FAR Part	Part 125
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 25 Flight Crew Total 7500 Flight Crew Type 2600
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Track / Heading All Types Inflight Event / Encounter CFTT / CFIT

Narrative:

The aircraft was on autopilot and we were in a descent to 3;000 feet. We were given direct to gliss. The aircraft made a large turn to the west (approximately 20 degrees past the heading that would take us to gliss) rather than heading for the fix. I was unsure what the autopilot was doing; so I disengaged it and started a turn back to the north to proceed towards gliss. Upon disengaging the autopilot; the aircraft was in the level off phase at 3;000 feet. As I was starting the correction for the turn; the descent continued to 2;700 feet before I realized we were still descending. I stopped the descent and started to climb back to 3;000 feet. At this time; we also received an 'obstacle ahead' GPWS warning for a tower located near the airport. While we were receiving the 'obstacle ahead' warning; ATC advised us that our altitude was low.we continued the turn back towards gliss and the climb back to 3;000 feet.I believe the turn to the west that the auto pilot did put us on a course to head towards the tower; rather than off to the right of it. In trying to figure out what was going on with the autopilot; I missed the level off altitude of 3;000 feet.

Original NASA ASRS Text

Title: SB-20 Captain reported receiving a GPWS obstacle warning while deviating from cleared track and altitude. Troubleshooting an autopilot issue was a factor in this incident.

Narrative: The aircraft was on autopilot and we were in a descent to 3;000 feet. We were given direct to GLISS. The aircraft made a large turn to the West (approximately 20 degrees past the heading that would take us to GLISS) rather than heading for the fix. I was unsure what the autopilot was doing; so I disengaged it and started a turn back to the North to proceed towards GLISS. Upon disengaging the autopilot; the aircraft was in the level off phase at 3;000 feet. As I was starting the correction for the turn; the descent continued to 2;700 feet before I realized we were still descending. I stopped the descent and started to climb back to 3;000 feet. At this time; we also received an 'Obstacle Ahead' GPWS warning for a tower located near the airport. While we were receiving the 'Obstacle Ahead' warning; ATC advised us that our altitude was low.We continued the turn back towards GLISS and the climb back to 3;000 feet.I believe the turn to the West that the auto pilot did put us on a course to head towards the tower; rather than off to the right of it. In trying to figure out what was going on with the autopilot; I missed the level off altitude of 3;000 feet.

Data retrieved from NASA's ASRS site 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.

Sb-20 captain reported receiving a GPWS obstacle warning while deviating from cleared track and altitude. Troubleshooting an autopilot issue was a factor in this incident.