Gulfstream IV / G350 / G450
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 30; Flight Crew Total 15200; Flight Crew Type 400
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
General None Reported / Taken
Procedure; Aircraft
While in cruise the Second Officer who was flying from the left seat decided to balance the fuel load. As per manufacturer's limitations; at this altitude; the only way to transfer fuel is to use a slight slip of the aircraft. Altimeters were checked before takeoff with the Captain's side (the Number 1) reading the same as the Co-pilot's side (the Number 2). At altitude the Number 1 side read FL450 and the Number 2 side read FL450; +60 FT. The First Officer (pilot flying) applied rudder trim to slip the aircraft. The Number 1 altimeter connected to the autopilot; which was flying the aircraft; stayed at FL450 the Number 2 altimeter rose to FLl450 +320 FT. The Number 2 altimeter at the time was feeding information to the transponder which transmitted a false altitude of FL450 +320 FT as the aircraft was still at FL450.
When the flight crew of a G-IV sideslipped the jet to transfer fuel while at FL450 the right side (First Officer's) altimeter indicated 45;320 FT verses 45;000.