G-V captain reported excursion from cleared altitude when the aircraft went into an uncommanded max ...

Attributes
ACN	1294367
Time
Date	201508
Local Time Of Day	1201-1800
Place
Locale Reference	ZOA.ARTCC
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Gulfstream V / G500 / G550
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	STAR RAZRR2
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 100 Flight Crew Total 6800 Flight Crew Type 3500
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance
Miss Distance	Vertical 2000

Narrative:

Cleared 'descend via RAZRR2 arrival; 30L transition' in ksjc. We were in level flight on LNAV; autopilot engaged. I selected VNAV to descend via the arrival as the descent path was ahead of the aircraft. This is a normal procedure in the G-550. For some reason yet discovered; the plane went into a max performance descent; vflch. I corrected the premature descent using vertical speed; staying on autopilot. We lost a little over 2;000 feet during the incident/recovery. I climbed the plane back up to previous altitude; but sequenced the next waypoint with lower altitude restrictions and just complied with that. I actually never made it back up to FL240 as it was no longer a valid part of the arrival.gulfstream is looking into this and hopefully we can understand why this happened.

Original NASA ASRS Text

Title: G-V Captain reported excursion from cleared altitude when the aircraft went into an uncommanded max descent.

Narrative: Cleared 'Descend Via RAZRR2 Arrival; 30L Transition' in KSJC. We were in level flight on LNAV; autopilot engaged. I selected VNAV to descend via the arrival as the descent path was ahead of the aircraft. This is a normal procedure in the G-550. For some reason yet discovered; the plane went into a max performance descent; VFLCH. I corrected the premature descent using vertical speed; staying on autopilot. We lost a little over 2;000 feet during the incident/recovery. I climbed the plane back up to previous altitude; but sequenced the next waypoint with lower altitude restrictions and just complied with that. I actually never made it back up to FL240 as it was no longer a valid part of the arrival.Gulfstream is looking into this and hopefully we can understand why this happened.

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.

G-V captain reported excursion from cleared altitude when the aircraft went into an uncommanded max descent.