Gulfstream IV / G350 / G450
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 40; Flight Crew Total 4500; Flight Crew Type 700
Communication Breakdown; Time Pressure
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
PIC loaded the VOR Approach. At first; he proceeded direct to the VOR 6 point; part of the procedure turn; when instructed to proceed direct to the VOR. However; this was resolved with FO input (reluctantly accepted by PIC); and we proceeded direct to the VOR 5;000 feet. PIC asked if we were cleared for the approach. I said 'Let me confirm'. Altitude alerter set at 5;000. ATC said: 'Maintain 5;000 to the VOR. Upon reaching the VOR; cleared for the approach.' PIC said to reset altitude selector to 3;500; which is the published VOR crossing altitude. Tone of cockpit up to that point was less than full CRM with PIC expressly stating that he preferred less input from FO. FO queried PIC; but PIC insisted on 3;500. As I recall; this was non-radar environment. ATC asked our altitude as we approached/crossed VOR. 4;000. ATC: You were instructed to maintain 5;000. I have traffic below you. Maintain 4;000 now.' Apparently; we still had acceptable separation at that point.CRM is important at all times and even MORE (not less) important when operating in foreign airspace (accents; unfamiliar procedures); and under the pressure of slot times (PIC seemed stressed about departure/arrival slot times).
Gulfstream IV First Officer reported they descended below the altitude they were cleared to on the LGMK VOR 6 Approach.