UAV - Unpiloted Aerial Vehicle
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 75; Flight Crew Total 2200; Flight Crew Type 500
Human-Machine Interface
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Human Factors; Aircraft
While operating an MQ-9 Unmanned aircraft system; I was level as assigned by Center at FL190. I designed a pre-program mission to allow the aircraft to loiter over a surveillance target. While designing the mission I mistakenly allowed the first waypoint of that mission to be left at its default altitude of 6;000 MSL. After giving the aircraft autopilot the instruction to fly the mission I immediately noticed its decreasing altitude. I immediately disabled the autopilot resulting in only a minimal altitude loss. I corrected the design of the operational mission; and thought that I sent it to the aircraft. However during that time I became distracted with a handover brief to another pilot. Before getting out of the seat to handover to the Relief Pilot I activated pre-program for the autopilot again. After trading seats I looked back at the altitude display to see that the aircraft had descended over 1;000 FT. The Relief Pilot saw it at the same time and commanded the aircraft to arrest its descent and climb back to FL190. The Center Controller contacted the aircrew to notify them of the altitude loss and the aircrew informed the Controller that the aircraft was returning to its assigned altitude.
MQ-9 pilot reports a programming error that results in a 1;000 FT altitude deviation before it's detected and corrected.