UAV - Unpiloted Aerial Vehicle
Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Confusion; Situational Awareness
Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Human Factors
Upon departing from Delta airspace; Tower switched Aircraft X over to Departure. Upon climbing; Departure advised Aircraft X to climb and maintain 10;000 feet. Shortly after Aircraft X was instructed to climb up to FL190; Aircraft X then read back the altitude of FL190. It was understood that Aircraft X was to climb and maintain FL190. FL190 was then programmed into the autopilot after that clearance was given. The instruments were crossed check; and autopilot was confirmed FL190 set. The aircraft was correctly climbing at 105 knots; 500 fpm; for FL190. Shortly after; departure switched Aircraft X over to Center. On initial call; it was communicated that Aircraft X was climbing out of 6;000 feet for FL210 (as that is what was filed). Center then replied that departure had given Aircraft X the wrong altitude and was to climb and maintain FL190. Aircraft X replied and confirmed FL190. Aircraft X also stated that departure had given the correct altitude of FL190; and that it was climbing for FL210 (as the flight plan was filed for FL210). This is where the communication error became apparent. Even though the autopilot was confirmed set at FL190 and that is what the pilot intended on doing; the way the statement to Center came across made them think otherwise. After that statement; Minneapolis Center gave Aircraft X a number to call. When in contact with Center on the phone the main concern to them was safety of flight. As the other Aircraft X was at FL200; when the call of 'climbing through 6000' for FL210' was made. The event ended without aircraft separation being broken. Accuracy and diligence in the phraseology to ATC is important. The Aircraft X should have initially communicated to Center 'Aircraft X (tail number) climbing out of 6;000 feet; for FL190; expecting FL210'. It is understood that the verbal read back needs to be for the altitude cleared to and not the altitude expected based on the flight plan filed.
UAV operator reported miscommunication with ATC while drone was inflight.