North sea helicopter ADS-B/MLat pilot project findings

The ADS-B installations on both aircraft are completely adequate. Equipment performance is consistent with governing TSOs, while aircraft installation aspects (antenna locations and RF characteristics) perform to expectations. The flights took place under worst case predicted RAIM conditions so that the minimum number of satellites would be visible, making any antenna masking noticeable. There is no evidence of GPS position loss. Degraded GPS reception close to two separate platforms was experienced when the S76 recorded significant HIL and HFOM reduction for approximately 60 seconds. This was attributed to satellite masking by the airframe. It has not been possible to positively identify which satellite(s) were masked during those periods. L-band masking was attributed to the wind turbines, when operating in their close vicinity and at approximate turbine hub height. Differences between the aircraft antenna installations were expected to cause discernable differences in operational performance, but this was not the case. Multilateration and ADS-B exhibited small position differences corresponding to the distance between aircraft GPS and L-band antennas. For the subject helicopters these differences are small (less than 10 m). Compilation of specific helicopter-oriented certification requirements in consultation with the authorities that will satisfy the current and intended service levels for off-shore operations is close to being finalised.