Gulfstream IV / G350 / G450
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 55; Flight Crew Total 8950; Flight Crew Type 4900
Human-Machine Interface; Situational Awareness; Training / Qualification
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
I was the Captain on the flight and was acting as PM; while the FO was the PF on this leg.  While descending in the arrival (was not descend via; simply following the arrival procedure); the aircraft was at FL80 (transition level was FL70) and was given a clearance to descend to altitude 5;000 feet on QNH of 995 mb.  The PF made the descent to altitude 5;000 feet and leveled.  ATC then made a call to us to maintain 5;000 feet.  I responded roger; maintaining 5;000 feet.  ATC then made another call to us that they showed us at 4;500 feet and to maintain 5;000 feet.  It was at that point that I realized our altimeters were still set to QNE 1013 mb.  We immediately made the correction and informed ATC of our incorrect altimeter setting.  They replied and said this would have to be a mandatory report of altitude deviation.  Looking back at this occurrence; there are a number of factors that caused this from my own errors and complacency.  This is a perfect example of the Swiss cheese model with all the holes lining up to this occurrence.  The factors are as follows:1.  Unnecessary distraction:  During cruise flight; I noticed the routing for our next Oceanic leg had an error.  I made a Satcom call to our flight planning provider to correct the problem.  As we descended above FL100; I made a radio call to the ground handler requesting services for our quick turn.  I then realized I forgot to mention to the handler that we needed them to print a hard copy of the new flight plan I had requested earlier with our flight plan provider.  Now level at FL80 on the STAR; I told the PF I was leaving the frequency again to call the local handler about printing our flight plan.  I knew better; and never should have left my PM duties below FL100.  Trying to avoid ground delays for flight plan delivery was simply not worth sacrificing removal of the PM.  It was at this time when I was off frequency that the PF took the radio call for the descent to altitude 5;000 feet without changing altimeter settings to QNH 995.  Had I remained on task; there would have been another set of eyes and ears to prevent this.2.  Electronic checklist:  I used the electronic checklist appropriately and all items were completed; crew briefing etc.  On the Approach Checklist; I had even left the one final item open and highlighted/displayed on the CAS which was 'Altimeters/Trans Alt'.  But again; due to getting distracted by leaving the frequency; I did not clear that final item of the checklist when leaving the transition level of FL70.  This checklist was in full view of us on the CAS when ATC first began calling about our altitude; but I missed it.3.  Improper Trans Alt in FMS:  The Honeywell FMS in the GIV allows for the setting of a transition altitude within the PERF feature.  The FMS then considers all altitudes above this setting to be FL's; and below this number are treated as altitudes.  The advantage to proper use of this feature is that the crew will receive an FMS scratch pad message stating 'check baro' if the barometer is set improperly when climbing or descending through the transition alt programmed into the FMS.  During cruise flight and prior to being able to receive ATIS with the current Transition Level; I entered the transition altitude from the STAR chart and placed it in the transition altitude selection within the FMS.  I never should have made that selection.  When descending; the Transition Level should always be set in the FMS.  When departing/climbing; transition altitude should be programmed in the FMS.  In this case; the transition level was FL70.  Had I set that number; we would have received a scratch pad message when leaving FL70 to 'check baro'.  Because I had set 5;000 feet; which happened to be our assigned altitude; we never got the alert because we hadn't yet descended through 5;000 feet as improperly set in the FMS. With the exception of the United States; most countries have a transition layer of at least 1;000 feet between the transition altitude and ATC assigned transition level.  Had I setup the FMS properly; we would have had a buffer between FL70 and the transition altitude of 5;000 feet to receive our FMS 'check baro' notification. Both myself and the PF missed the QNH altimeter setting.  Two professional pilots didn't get the proper setting due to a number of factors that individually would not be a big deal.  But when added up; these factors took away the many mitigation strategies we have to keep this from happening.  There are a couple areas that we could make improvements in our SOPs to prevent this in the future.  We need to learn and get better from this unfortunate event.
Captain reports forgetting to change the altimeter barometric setting passing through the transition level during descent into a foreign airport; due to VHF communication with the handler. The First Officer was the pilot flying; and accepted the ATC clearance below the transition level without changing his altimeter setting.