Uav operator reported misprograming the uav causing it to descend unintentionally.

Attributes
ACN	1471822
Time
Date	201708
Local Time Of Day	1201-1800
Place
Locale Reference	FSD.Airport
State Reference	SD
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	UAV - Unpiloted Aerial Vehicle
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	Pilot Flying
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 22 Flight Crew Total 3000 Flight Crew Type 1500
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

I put the aircraft on a pre-programmed mission with altitude set to FL270 and airspeed set to 83 KIAS. The altitude was not properly propagated to one of the points on the mission and I missed that. Turning to point 3; the aircraft started descending from FL270 and went as low as FL254. Center called as I was doing a manual take over and climbed back to the assigned altitude fixed the mission and continued over the area of interest until a crew swap out 2 hours later.the location was approximately 20 miles north of sioux falls; sd.

Original NASA ASRS Text

Title: UAV Operator reported misprograming the UAV causing it to descend unintentionally.

Narrative: I put the aircraft on a pre-programmed mission with altitude set to FL270 and airspeed set to 83 KIAS. The altitude was not properly propagated to one of the points on the mission and I missed that. Turning to point 3; the aircraft started descending from FL270 and went as low as FL254. Center called as I was doing a manual take over and climbed back to the assigned altitude fixed the mission and continued over the area of interest until a crew swap out 2 hours later.The location was approximately 20 miles north of Sioux Falls; SD.

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.