EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Fatigue; Confusion; Communication Breakdown
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Human Factors
We were cruising at FL280 and were instructed by Center to cross 20 miles south of MZZ VOR at FL260 and increase speed from 270 KIAS to 280 KIAS. I read back the instructions. I'm not sure if I read back FL260 or FL200. But the First Officer set FL200 as the altitude to descend to and I verified. As we were descending through FL250 to meet the crossing restriction ATC asked us to maintain FL260. I queried him on our clearance; which I thought; and the First Officer thought; was FL200; but he said it was FL260. He then asked us to level off at FL240. We continued the flight with no other issues.The way the Controller read the instructions; there were a lot of 'numbers' I had to remember and I feel I mixed them up. With the 20 mile crossing restriction; the altitude change the speed increase all in one breath; I mixed them up and instead of FL260 we used FL200. Another threat to the flight was that we were on our 5th of 6 legs for the day and had been dealing with winter operations the whole day making the day feel longer. I learned that next time I get a long clearance in one breath I should double check with the controller to make sure I read back all the instructions correctly. I should also double check with the First Officer to make sure he heard what I heard.
EMB145 Captain reports misunderstanding a descent clearance with a crossing restriction based on distance and a speed adjustment. The First Officer misunderstands in a similar fashion and the clearance is not questioned; resulting in as descent below assigned altitude.