Unmanned RQ4A global hawk aircraft has an altitude deviation.

Attributes
ACN	727848
Time
Date	200702
Place
Locale Reference	navaid : bab.tacan
State Reference	CA
Altitude	msl single value : 23000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : nct.tracon
Operator	other
Make Model Name	Military
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 16
ASRS Report	727848
Person 2
Affiliation	government : military
Function	flight crew : single pilot
Events
Anomaly	non adherence : clearance
Independent Detector	other controllera
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft departed AFB climbing to FL230; leaving 15000 ft the pilot (on the ground) had a question about what altitude to maintain. I told him to maintain FL230 and told him to contact oakland center. A few mins later the pilot reported back on my frequency and I told him to contact oak center again. I observed the aircraft leave FL230 and he reported back on my frequency and said he had radio problems. Aircraft is a global hawk aircraft (unmanned) and was supposed to stay level at FL230; but went to FL237 then back to FL230.

Original NASA ASRS Text

Title: UNMANNED RQ4A GLOBAL HAWK ACFT HAS AN ALT DEV.

Narrative: ACFT DEPARTED AFB CLBING TO FL230; LEAVING 15000 FT THE PLT (ON THE GND) HAD A QUESTION ABOUT WHAT ALT TO MAINTAIN. I TOLD HIM TO MAINTAIN FL230 AND TOLD HIM TO CONTACT OAKLAND CTR. A FEW MINS LATER THE PLT RPTED BACK ON MY FREQ AND I TOLD HIM TO CONTACT OAK CTR AGAIN. I OBSERVED THE ACFT LEAVE FL230 AND HE RPTED BACK ON MY FREQ AND SAID HE HAD RADIO PROBS. ACFT IS A GLOBAL HAWK ACFT (UNMANNED) AND WAS SUPPOSED TO STAY LEVEL AT FL230; BUT WENT TO FL237 THEN BACK TO FL230.

Data retrieved from NASA's ASRS site as of January 2009 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.