Citation X (C750)
Flight Crew Air Transport Pilot (ATP)
Fatigue; Situational Awareness; Communication Breakdown; Distraction
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Human Factors
During the arrival phase we were descending from 3;000 FT to 2;000 FT when we received a terrain warning on the GPWS at 2;200 FT. We responded to the warning by climbing and the warning quickly ceased at about 2;500 FT. I asked Approach Control about our altitude assignment and he instructed us to return to 3;000 FT. He was very calm and pleasant throughout. I believe we mistakenly accepted a clearance issued to another aircraft which was descending into TEB. It is likely that my readback was blocked and the Controller was unaware of our descent. My lack of attentiveness may have been due to the onset of fatigue. We were delayed almost 3 hours leaving our departure airport because of heavy holiday departure traffic; resulting in a longer day than anticipated.
A fatigued CE750 Captain reported responding to an EGPWS Terrain Warning at 2;200 FT after mistakenly taking an other aircraft's clearance when they should have been at 3;000 FT.