Gulfstream IV / G350 / G450
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 95; Flight Crew Total 15000; Flight Crew Type 6000
Communication Breakdown; Confusion; Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Aircraft; Human Factors
We were flying our first trip using CPDLC (Controller Pilot Datalink Communications). Approximately 78 miles west of the DIALO intersection cruising at FL410. We sent a request for FL430. ATC replied unable due to traffic. [Later] we received the message 'standby your traffic is climbing.' [A few minutes later] we received the message 'your traffic is moving.' Shortly after receiving [that] message we received a message that both I and my First Officer interpreted as a clearance to climb to FL430. We initiated a climb rate of approximately 300 fpm. Passing approximately 41;800 feet we received a message to descend to maintain FL410. We immediately initiated a descent and returned to FL410. [We then] received the message 'maintain FL410. Possible higher once traffic moves.' [Shortly thereafter] we received the message 'climb to and maintain FL430.'Both myself and my First Officer are perplexed with this series of events. We both saw a message which we both interpreted as a climb clearance. We both saw a message instructing us to descend to FL410. Neither of these two messages are stored in the message log.
[Report narrative contained no additional information.]
GIV flight crew reported departing cruise altitude without a clearance due to confusion with CPDLC communication.