B777  Duplicated ADS-C Reports

We are seeing a large number of duplicated ADS-C reports where the same ADS-C report is received twice or on occasion three times with variable delays between the first and duplicated reports. This has the effect of skewing performance data from these aircraft unless the duplicated reports are filtered.

An analysis carried out January-October 2008 in NZZO has identified 1289 duplicated reports. 1061 or 82% of these are coming from B772/3 aircraft which only make up around 39% of total traffic.

Type	# Duplicates	% Duplicates	% Traffic
A332	37	3	1.5
A340	48	4	19
B744	142	11	38
B777	1061	82	39