Basic Aeronautical Knowledge: Altimetry and margins of error
Thread Starter
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!
I would have thought it would be a relatively easy exercise to have it thrown out of court without an excessive waste of 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!
In the real world, Cedrik, a real Australian pilot is being prosecuted for ‘low flying’. My understanding is that the pilot is the pilot to whom the CASA person I quoted earlier was referring when he said to a Senate Committee: “[T]hat’s not what the instruments on his aircraft say. They say he was at 125 feet.”
I confidently predict that the pilot isn’t you, Cedrik, because rather than carrying on like a petulant child as you are in the threads I’ve started, you’d be under constant stress, having sleepless nights and spending large to defend yourself against an allegation you consider to be untrue. Maybe you’d end up like Glen Buckley: a heart attack and penniless as a consequence of what’s been done to you. Pray your turn never comes.
I confidently predict that the pilot isn’t you, Cedrik, because rather than carrying on like a petulant child as you are in the threads I’ve started, you’d be under constant stress, having sleepless nights and spending large to defend yourself against an allegation you consider to be untrue. Maybe you’d end up like Glen Buckley: a heart attack and penniless as a consequence of what’s been done to you. Pray your turn never comes.
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.
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.
Moderator
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.
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.
Thread Starter
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.
(Chronic Snoozer nailed it by nominating the RADALT as the most accurate gizmo to measure the distance between a point on an aircraft’s airframe and the ground or water. These days I think the margin of error in RADALTs is specified in centimetres. But why do some aircraft have RADALTs? Precisely because the other gizmos aren’t precise enough when an aircraft is getting close to the ground in zero or bad viz.)
As the CASA person who made the statement in front of the Senate Committee wasn’t in the aircraft with the pilot, the CASA person can’t be referring to the aircraft’s altimeter or the display on the aircraft’s transponder. As the pilot involved denies the allegation, I can only assume - reasonably I suggest – that the pilot doesn’t reckon the altimeter was "saying" 125’. I can only assume – reasonably I suggest – that the CASA person was referring to some gizmo on the ground relying on Mode C transponder / ADS-B data.
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Thread Starter
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 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’?
Moderator
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.
Based on my limited observations over the years, I doubt the exercise would be likely to proceed much beyond lodging a defence.
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 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’?
Per the standard, for altitudes below 50187.5 ft it is in 25 ft increments, above that it is 100 ft.
Thread Starter
Thanks swh.
Thread Starter
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:
