Yes, I remember watching the AN124 display at the RAAF Richmond Airshow in 1988. It looked to me like it was tootling around at about 30 Kts!I would have thought that it should not have got to court in the first place. However, the same pilot is, on my understanding, also being prosecuted for operating contrary to the aircraft's AFM - in excess of VNE - on the basis of groundspeed recorded on the ground and forecast winds. If that's correct, my view is that these prosecutions are, at best, based on a 'fail' standard of BAK and, at worst, a deliberate 'hatchet job' by people who know full well the kinds of tolerances and margins of error of the equipment and variables involved but have chosen not to explain that in detail to the CDPP. However, I hasten to reiterate that there are always at least three sides to every story. Perhaps there is some 'smoking gun' evidence in the form of, for example, a qualified pilot who was also in the aircraft at the time.

Your point about strict liability is a stark one in the circumstances of 'low flying'. It's a strict liability offence. A diligent pilot operating a serviceable aircraft can inadvertently breach the minimum height rules and it's still an offence. Easy example: VFR aircraft with an altimeter that 'overreads' by 50' and everything else is 'perfect and accurate' including the QNH. Cruising at 500' 'indicated' over the sea is actually only 450'. Strict liability offence.

Ironically, when all the tolerances and margins are the other way, a pilot could decide to do a 'beat up' at 250' indicated but actually be 500' above the water!

Petulant child I might be, I have also been around GA long enough to know you can't fight CASA. If you do they will break you as in the example you quote, if your right or wrong it doesn't matter. They will destroy you.

As for the rest of your post, I get lost in the technicalities, I blame my dyslexia.

Maybe you could put your analytical skill and knowledge of aviation law into helping Glen B.

This could be considered ‘an honest and reasonable mistake of fact’, and would be grounds for a successful defence, even in a strict liability matter.

I would have thought that it should not have got to court in the first place.

Unless there is more to the story than what is disclosed, one might think so.

operating contrary to the aircraft's AFM - in excess of VNE - on the basis of groundspeed recorded on the ground and forecast winds.

That would have to be an interesting argument for it to prevail, methinks. Again, one starts with an appropriately knowledgeable solicitor.

but have chosen not to explain that in detail to the CDPP.

Were that the case, it would be foolish in the extreme as the defence would shoot it full of holes ?

strict liability

Defences are still available. 6.1 Strict liability | Attorney-General's Department (ag.gov.au)

The rule just makes it harder to defend the accusation and easier for the prosecution to prevail in court. Again, a requirement for an appropriately experienced solicitor.

Interesting point.

Bizarrely, if you did the pre-flight altimeter check and knew that it was overreading by 50’, the defence might not work. But if you took off from some place where the check couldn’t be done and you didn’t know about the 50’ overread, the defence might work. The difference in objective safety risk is, of course, zero.

RADALT can also read the height above the terrain below the water, not always the height above water, you can see that sometimes coming in over water to land.

The ADS-B data packet can contain the encoded pressure altitude which is either in a 25 or 100 ft resolution in ft, or the GNSS height above the WGS-84 geoid in meters. If they are basing the 125' off GNSS, if the aircraft is in south west Australia it could under read by around 330 ft, and NE Australia over read by 330 ft. A line through around Hobart, Adelaide, Alice Springs, Port Headland would have close to zero difference between the WGS-84 geoid and MSL.

Thanks swh.

What determines whether an ADS B data packet transmitted by an aircraft ‘chooses’ the encoded pressure altitude rather than the GNS height above the WGS-84 geoid? And if the encoded pressure altitude is transmitted in the ADS B data packet, what ‘chooses’ and how is the 25’ versus 100’ resolution ‘chosen’?

What this discussion highlights is that the defence would/should obtain a detailed and technically competent engineering report on system/equipment accuracy/precision and, I daresay, shoot the prosecution's case somewhat out of the water (presuming that the pilot was, indeed, operating in a reasonable manner at the relevant time).

Based on my limited observations over the years, I doubt the exercise would be likely to proceed much beyond lodging a defence.

The default is encoded pressure altitude, if the encoded pressure altitude is not available GNSS height will be transmitted. Similar with speed the default is GNSS ground speed, and track is computed from the resolving the easting and northing ground speed. In the absence of GNSS ground speed it will transmit IAS and heading if this data is available.

Per the standard, for altitudes below 50187.5 ft it is in 25 ft increments, above that it is 100 ft.

Thanks swh.

It's been a very long time since I saw one of Ronnie's finest do a 'beat up' at 25', but this 'evidence' is compelling:

https://cimg8.ibsrv.net/gimg/pprune....ec9a2dc996.jpg