yes it is curious. if there has been an explanation I have missed it. aircraft carries ulb. its range is 1 to 2 km in normal conditions. ulb signal is heard so the bearing of it from the tpl is known but not the range but hey we dont need that, it says on the tin it is no more than 2 km away. textbook stuff so far but ulb and aircraft not found. it seems ocean shield and echo together could not establish even a position line. how did this or any other ulb get certificated with such a dismal specification? apparently the number of successful ulb locations via pinger, ever, can be counted on one hand. just another piece of kit to add to the list of recommended upgrades. so its got to be the hard way, the ulb is obviously down there somewhere so its now a long slog to find it a la af 447.