<< >> NASA ASRS Report 1444857, April 2017

G-V flight crew reported the autopilot initiated an unwanted 300 foot descent from the selected altitude.

Attributes
ACN	1444857
Time
Date	201704
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Gulfstream V / G500 / G550
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Experience	Flight Crew Last 90 Days 20 Flight Crew Total 14800 Flight Crew Type 400
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 25 Flight Crew Total 9000 Flight Crew Type 300
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude

Narrative:

This aircraft had just been accepted from gulfstream. The crew had done a post acceptance flight and everything was working properly. When arriving [at destination] we were on vectors for left downwind to runway xxl. We had the autopilot on and level at 4000 feet. The autopilot began to lower the nose inadvertently and we lost 300 feet prior to regaining control and getting back up to 4000 feet.

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Original NASA ASRS Text

Title: G-V flight crew reported the autopilot initiated an unwanted 300 foot descent from the selected altitude.

Narrative: This aircraft had just been accepted from Gulfstream. The crew had done a post acceptance flight and everything was working properly. When arriving [at destination] we were on vectors for left downwind to Runway XXL. We had the autopilot on and level at 4000 feet. The autopilot began to lower the nose inadvertently and we lost 300 feet prior to regaining control and getting back up to 4000 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.