Preliminary report VH TNP
 

Does any of you ATCers know whether the Radar track of 250 degrees is True or Magnetic? 250M would put them way NORTH of BLA.

My handy-dandy pocket thingy says YJBY-YBLA 235M & 248T, so the figure quoted is a bit of a mystery. Unusual for anybody to put such slap-dash stuff in a report, however preliminary. If this is what was replayed off the 'radar tapes' it would be worth noting the enroute consoles are all oriented to true north rather than magnetic.

Rhumb Line is 250 True from JBY to YBLA.

From abeam Ulladulla (not a JBY) it was cleared to BLAED.....

Thank you I thought that might have been the case. It just had me wondering because they do give us magnetic headings to steer. Do they have to convert T to M in their heads?

GPS
 

Does anyone know of a parallel track can be set up on an IFR approach?

Not the one TNP was conducting.

I do not know what equipment was fitted to the aircraft in question, but all IFR (TSO C129) GPS's I am familliar with (Garmin and King) do not have the capability to fly offset tracks, and I would seriously doubt whether any with that capability would allow that when flying an approach.

When flying a random track like that being flown there would be no need to offset a track anyway.

The only GPS's I know of which have the offset track feature are handleld VFR gps units, such as my garmin 196.

Bevan..

Most of the newer GPS units do not allow an offset to be selected.

In this instance ASTB has stated that the aircraft was 3.83 degrees offtrack all the way from Jervis Bay.

Offset tracking on older GPS units only allows parallel tracking ie selecting a distance of track eg 2nm and this is held constant until the offset is cancelled.

If the waypoint BLAEG was inadvertantly selected rather than BLAED this would put the aircraft about 2 degrees left off track, but not 3.83.

Tracks/ Distances:
YJBY- YBLA 235M 244nm
YJBY- BLAED 235M 230nm
YJBY- BLAEE 234M 229nm
YJBY- BLAEG 233M 234nm

3.83 degrees off track over 230nm by 1:60 would be 14.69nm south of track. Would be interested to know exactly where it crashed. I believe it was last seen on radar 10nm east of BLAEE at 5000'.

This would put it right on the edge of the 25MSA limit which is 5000'.


Whilst safe it would be unusual for an experienced pilot to be at this level so early as the approach starts at 5000'.

Appreciate any comments

BH

Also, an interesting (apparent) contradiction in the preliminary ATSB report in that in the second paragraph states that "..From a position abeam Ulladulla, the flight was cleared direct to the global positioning system (GPS) initial approach point BLEAD (ED)...", and in the last paragraph it states that :"...radar data indicated that the aircraft had tracked 250 degrees from Jervis Bay to a point where it disappeared from radar."

Flying from Bankstown to Jervis Bay - a position "abeam Ulladulla" is actually 9 Nautical Miles PAST Jervis Bay, so - are we to believe that the pilot made a turn towards BLEAD about 3 minutes PRIOR to receiving a clearance to make such a turn??

It is also puzzling why a controller would issue a clearance from Ulladulla (or Jervis Bay) to BLAED, as this routing would necessitate two BIG doglegs during the approach - first a left turn of some 45 degrees from 238 degrees (magnetic) to 193 degrees to get to the IF (BLAEI), followed by another 70 degree turn to the right to intercept the inbound track of 263 degrees magnetic, when in fact a routing from Jervis Bay to waypoint BLAEE (which also has the only holding pattern depicted for the approach) would only involve a very minor course correction of some 25 degrees to the right after the Initial Approach Fix (BLAEE) to get established on the inbound track of 263 degrees magnetic.

I have never seen ATSB (or any other similar agency for that matter) release explicit details of this nature at such an early point in the investigation and would be very interested in the motivation for them doing so on this occasion.

This was probably done on request from the PIC, and looking at my charts it was the waypoint closest to the direct track from jervis bay to benalla.

Bevan..

Bevan - yes, you are probably right, seeing that ED is closer to the direct track. I understand that the regular flight from Bankstown to Benella tracked out from Bankstown through Katoomba-way, so ED was probably the IAF most frequently used for the approach. Did not attempt to speculate, - was just thinking loud as I was looking through the flight and the waypoints indicated in the ATSB report.

ATSB
 

WA AV8R,

As you think aloud some more, why do you find it strange the ATSB released information so early?:confused:

Perhaps they have a possible cause, and now making the evidence fit, and drip feeding it to the masses, both educated (pilots) and non educated (media).

Most detective work goes the other way, but ah well.

Sounds like the methodology employed about 4 years ago :yuk:

Muddergoose,
I do not wish to speculate, but with all due respect to the many competent professionals at ATSB, expediency is probably not the one characteristic that springs to mind when describing the organisations main attributes.

Hence, my surprise at the release of these early findings was caused by the timing as well as the fact that they are at the same time very explicit (3.83 degrees off an alleged cleared track) and apparently contracticory (were they at Jervis Bay or Ulladulla when clearance to track direct to BLAED was issued?) The conjecture that i read into the preliminary ATSB findings published, is that the pilot had set off tracking towards somewhere else than where ATC had given him clearance to go, and I just would like to see the ATSB being specific about where he was when the implied navigation error originated.

Speculating a bit, taking Bindooks 14.7 nm south.

If we look at:

Spherical geometry
Data storage
Software functions

The usual method of handling angles as in lat is from the N pole in radians and a convenient way of storing it would be 3 bytes in microradians

For BLAED at ~ S36:29 this would be 126.48 deg or &H21AF3E uradian, the A would be 1010 in binary. Flip one bit to 1011 to get B and we have &H21BF3E which translates to ~ S36:43.

Without knowing exactly how the GPS storage and calculation all works internally it is difficult to say but this change could occur either in the card or in intermeadiate (RAM, EEPROM or Flash) storage for the leg. As to what could flip the bit the current size/charge of bit storage these days means cosmic rays or radioactive decay on an atom within the chip/packaging can do it.

An interesting exercise for ASTB.

For King GPS's the internal calculations inside the actual GPS reciever use 4 byte (32 bit) floating point numbers to represent lat and long, and all velocity values. Dont ask my why I know.

I am not sure of the data storage in the flash in the front end of these units, but surely they have some form of checksumming on the aviation data to protect against these sort of errors.

Bevan..

I was told something about one angle the direction of the investigation this evening by a reliable source.

It has nothing to do with the pilot, its a technical matter and it is yet to be proven, but I hesitate about posting anything about it at present. Unless I can confirm it is not going to drive everyone into a paroxysm of rage.

Sunfish,

I too have heard this rumour. What is disturbing (as people have been saying above) is that the type of data released to date is implying that this is the direction being taken.

CS