Gulfstream IV / G350 / G450
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 75; Flight Crew Total 5500; Flight Crew Type 750
Communication Breakdown; Fatigue
Deviation - Altitude Overshoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
We were given an initial descent from FL450 to FL430 on the MOD5 arrival. The incident occurred between OAL and INYOE. As the pilot in command I misheard the communication and thought we were cleared to FL320. I noticed the First Officer change the altitude pre-select but I did not verify what number was put in the window. I initiated a Vertical Speed descent of 1500 FPM and disconnected the autothrottles to keep from over speeding. I called for the descent checklist which was run by the First Officer.I was preoccupied with the speed in the descent because of the autothrottles being off. I was not monitoring the vertical descent since that was hard selected at 1500 FPM but I noticed the speed all of sudden started dropping from my target of .8M to .77M very quickly. At that moment I noticed we were level at FL430 and I looked at the altitude pre select which said FL430. I manually initiated another VS descent still thinking we had been cleared to FL320. I asked the first officer why 430 was in the preselect window and he stated that was what were cleared to. I called Oakland center and ask for a clarification on our altitude to which [they] verified FL430. I disconnected the auto pilot and initiated a climb. The deviation was 750 FT below assigned altitude. I believe the cause was twofold:The primary reason for the deviation was failure by both the Captain and the First Officer to follow proper procedures in verifying and verbally confirming assigned altitude; and vertical mode in use. A second contributing factor was an early morning departure which and multiple maintenance issues with the airplane which contributed to the fatigue. Both the Captain and the First Officer received very little sleep and were at the airport [early] morning for departure. (Assigned crew rest was not a factor)
[Report narrative contained no additional information.]
Gulfstream IV flight crew reported flying through cleared altitude when the pilot flying misunderstood the descent clearance.