A method comprises computing position information from a global navigation satellite system (GNSS); computing an altitude measurement based on retrieved information from a vertical position sensor; determining a vertical protection level (VPL) associated with the position information; splitting the VPL into an upward VPL component and a downward VPL component; determining a vertical alert limit (VAL) associated with the altitude measurement; and splitting the VAL into an upward VAL component and a downward VAL component. The method optimizes an integrity budget allocation between the upward and downward VPL components. The method then recomputes the upward and downward VPL components given the optimized integrity budget allocation.