EMB ERJ 145 ER/LR
Communication Breakdown; Situational Awareness; Physiological - Other; Fatigue
Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance
Human Factors
We were level at FL310 when we were cleared to cross 40 miles south of VXV at FL240. I was pilot not flying and read back the clearance to ATC. The Captain set FL240 in the preselect and we verbally confirmed '240 set' and 'cross 40 miles south.' I then saw him put a fix in the FMS 40 miles south of VXV. At this point I was stopped paying close attention to the restriction because I felt that he had the ability to make the restriction so I didn't think much more about it. After several days of flying together; I had become complacent about monitoring the Captain as I had been impressed with how 'by the book' and sterile he keeps the cockpit.The Captain noticed when we were quite close that we hadn't started descending. He immediately initiated a rapid descent and advised ATC we couldn't meet the restriction. ATC responded with 'do your best.' I believe we crossed 40 south around FL260. It was our second day of waking up at 0430 to catch a 0500 van ride. We were flying with 30 minute turns with no time to catch our breath or eat. I was definitely starting to feel tired and hungry on the leg back to Cleveland. This certainly contributed to my lack of attention. Additionally I had flown the first two legs of the day; and relaxed myself a little as I was then pilot not flying for the last 2 legs of the day. All of these factors contributed to my lack of situational awareness. I failed to focus on the task at hand; and must strive to maintain vigilance as pilot not flying in the future.
An ERJ flight crew failed to initiate a timely descent and was unable to comply with an ATC crossing restriction. Fatigue and lack of nutrition were cited as contributing factors.