Narrative:

There was forecast to be some turbulence along route. Around XA20 we discussed climbing because we were starting to get moderate chop and light turbulence. The captain sent the cpdlc (controller pilot data link communication) message and requested FL360 due to weather. While waiting for instructions; we noticed an aircraft behind us on TCAS (traffic collision avoidance system) at FL360. I verbalized that the request will get denied due to traffic. At XA23 we got the message that said 'unable requested altitude due to traffic' all in caps like all ATC cpdlc messages. Below that line there was 'climb and maintain FL350' in all lowercase. We saw the unable and accepted the message. The climb instructions were not observed and we maintained FL340. At XB15 we received a message to confirm altitude; you were cleared to climb and maintain FL350 about an hour ago. The captain and I then went through all the log and found the missed clearance. We coordinated with ATC and determined we would stay at FL340. The confusion on my part came into effect because we [were] used to seeing instructions from ATC in all caps and the previous message below [was] in lower case. The message that cleared us to climb and maintain FL350 was not in the same format as other messages we received. The unable climb portion in all caps and then the climb and maintain in lower case led me to believe that was the previous message. I went back though all of our ATC messages and they all followed that same format with ATC in bold and our response in lower case.

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Original NASA ASRS Text

Title: B737 flight crew reported missing clearance from ATC to climb.

Narrative: There was forecast to be some turbulence along route. Around XA20 we discussed climbing because we were starting to get moderate chop and light turbulence. The Captain sent the CPDLC (Controller Pilot Data Link Communication) message and requested FL360 due to weather. While waiting for instructions; we noticed an aircraft behind us on TCAS (Traffic Collision Avoidance System) at FL360. I verbalized that the request will get denied due to traffic. At XA23 we got the message that said 'UNABLE REQUESTED ALTITUDE DUE TO TRAFFIC' all in caps like all ATC CPDLC messages. Below that line there was 'Climb and maintain FL350' in all lowercase. We saw the unable and accepted the message. The climb instructions were not observed and we maintained FL340. At XB15 we received a message to confirm altitude; you were cleared to climb and maintain FL350 about an hour ago. The Captain and I then went through all the log and found the missed clearance. We coordinated with ATC and determined we would stay at FL340. The confusion on my part came into effect because we [were] used to seeing instructions from ATC in all caps and the previous message below [was] in lower case. The message that cleared us to climb and maintain FL350 was not in the same format as other messages we received. The UNABLE CLIMB portion in all caps and then the climb and maintain in lower case led me to believe that was the previous message. I went back though all of our ATC messages and they all followed that same format with ATC in bold and our response in lower case.

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.