PilotAware
British Forum => Technical Support => Topic started by: Gary Nelson on October 29, 2017, 05:58:29 am
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If you are flyinging in an area outside say a LARS, does this mean transponders in other planes are not being interrogated and therefore silent, so that Pilot Aware won't detect them - or have I totally misunderstood this?
Secondly, if another plane is in the same area that has equipment to detect Mode C/S, will this "wake-up" the the other transponders in the area, so I can then, in theory, detect them with my own Pilot Aware?
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Hi Gaz
Mode C/S will only transmit when interrogated as you suggest so if they are not interrogated PilotAware nor any other 1090 receiver will not pick them up.
If the interrogation wakes up Mode C/S then you will.
Pilotaware, ADSB and Flarm are continuously transmitting without needing interrogation.
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If you are flyinging in an area outside say a LARS, does this mean transponders in other planes are not being interrogated and therefore silent, so that Pilot Aware won't detect them - or have I totally misunderstood this?
Secondly, if another plane is in the same area that has equipment to detect Mode C/S, will this "wake-up" the the other transponders in the area, so I can then, in theory, detect them with my own Pilot Aware?
Gaz,
Along the right lines, but not quite correct. Interrogation (and therefore responses - which is what we are interested in) still occur outside the physical area in which a LARS service is provided if the area the aircraft is in is 'covered' by any 1030/1090MHz radar head - civil or military, though in outlying areas on the periphery of radar coverage, or in radar shadows such as mountain valleys, coverage can be at best intermittent. Thankfully, most of the UK (outside the wilds of Scotland and some of the Welsh valleys) is pretty well covered by radar, though not necessarily right down to ground level. This is one of the reasons why we often don't get responses from very low-flying aircraft or transponders on the ground.
As Keith says, transponders can also be 'triggered' by TCAS systems fitted in overflying commercial aircraft and some 'Biz' types. The transponder will then produce 'normal' responses which can be picked up and used by PilotAware.
Mode 'S' transponders do also transmit their 'Hex ID' automatically approximately once per second, via what is known as a 'short squitter'. This is independent of radar interrogation, but the Hex ID alone doesn't give enough information to be useful to PilotAware as there is no location or altitude information provided. (We don't usually mention this because it tends to confuse the issue, but it has been raised in other recent threads, so I include it here for completeness).
Best Regards
Peter
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Thanks for helpful replies