Study on second HMU: some aspects of height monitoring during the verification stage of the RVSM implementation strategy above FL290

Different monitoring scenarios for use during the verification stage of the RVSM implementation strategy for the North Atlantic MNPS airspace have been examined. Special emphasis was put on the use of a single HMU versus two HMU's at two different locations. The use of a second HMU contributes to a more representative sample. Choices for the best and second best locations for HMU's have been described