Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Communication Breakdown
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance
Human Factors
Controller pilot datalink Communication (CPDLC) instruction was 'Cleared to ZZZ APRT LGA5 EXCEPT TURN LEFT HDG 360 FOR RV THEN AS FILED'. When I received and acknowledged the clearance; I read it to the Captain stating EXPECT TURN TO 360 instead of EXCEPT ....' Nothing more; the Captain read the CPDLC and acknowledged what we briefed. Captain was PF. We were cleared for takeoff from Runway 4 and we commented that usually they state 'turn to heading ###'; however; Tower frequency was too busy to inquire and in the absence of further instruction we turned to the SID heading of 051 degrees. Once transferred to Departure Control; he gave us a heading of 360 degrees. A few minutes later; Departure Control requested to know what heading we were assigned by LGA Tower; and I stated 'We weren't given a heading but CPDLC stated to expect a heading of 360 degrees.'  Nothing more was said. Thirty minutes passed; and I decided to reread the CPDLC and noticed my error of reading 'Expect' instead of 'Except'. No excuses; I was wearing my new glasses and it was light outside; there were no stressors during boarding. I plainly misread the clearance. We read what we think we want to see and perhaps my only recommendation would be: 1. First Officer to be more thorough.2. I wish they (Clearance) could use different verbiage and 3. Tower could reinforce the change to the standard clearance but I know LGA is BUSY.'
First Officer reported a track error departing LGA citing error in reading CPDLC change of initial heading during predeparture briefing as probable cause.