Ozrunways Question

[Ozfergie]

I think this has appeared since I turned on the LSALT boundary - now dotted around the map view I can see combinations of a LARGE numeral with a smaller numeral to the top right - combinations are various and also appear either in pink or red - what are these?

 

 

[Birdseye]

Only a guess.....Minimum Safe Altitude?

 

 

[Nightmare]

The big number would be 1000's ft and the smaller one 100's ft the grid's Lowest Safe Altitude with the boundaries with the grey box. Same as the ERC Low which have them depicted in green. Not sure what the colour coding is with the red and pink

 

 

[Ozfergie]

The big number would be 1000's ft and the smaller one 100's ft the grid's Lowest Safe Altitude with the boundaries with the grey box. Same as the ERC Low which have them depicted in green. Not sure what the colour coding is with the red and pink

That sounds logical but I don't think that is what I am looking at - otherwise it is telling me that the Lowest Safe Altitude over the YCNK/YDEN area is between 5,600 and 6,600 feet

 

 

[Birdseye]

That sounds logical but I don't think that is what I am looking at - otherwise it is telling me that the Lowest Safe Altitude over the YCNK/YDEN area is between 5,600 and 6,600 feet

I don't have full maps of that area, but just to the North of Maitland its 6500, presumably based on Mt Barrington.

 

 

[Chris SS]

It's called a grid LSALT.

 

The lowest safe altitude (LSALT) is 1000' aboxe the highest obstacle in a 10nm radius from that point. The grid LSALT is the lowest LSALT in a 4 block grid on the chart.

 

In essence it meanse that if you are anywhere in the grid at that altitude, you will be at least 1000 feet above every point.

 

Please note that this is a simplified explanation. There is more to the calculation when comsidering high structures as well.

 

 

[ian00798]

It is definitely the grid lowest safe altitude. The grid lowest safe altitude that Cessnock is in is definitely that height and that's because it has to take into account the highest terrain in that entire grid. If you went and calculated a route lowest safe you would quite likely end up with a lower figure unless your route actually took you near that high point.

 

The grid lowest safe also takes into account high structures as well, the same way any other LSALT calculation does, so if you are at the grid lowest safe altitude with the correct QNH set you are guaranteed 1000ft of obstacle clearance.

 

 

[Awqward]

Since it is legally possible for there to be an unmarked structure up to 299' you normally add 1000' to the highest structure OR 1300' to the highest terrain....whichever is higher...

 

 

[ian00798]

Since it is legally possible for there to be an unmarked structure up to 299' you normally add 1000' to the highest structure OR 1300' to the highest terrain....whichever is higher...

Actually it could be 360 feet tall, hence add 1360 feet to get LSALT. Unless the highest point in the area happens to already be a structure of greater than 360 feet, in which case you just add 1000 feet.

 

 

[ben87r]

And no less than 1500'

 

 

[Awqward]

Fair enough ...360' must be an Australian thing...

 

 

[ben87r]

Fair enough ...360' must be an Australian thing...[/quoteWe usually do have to 'ozzify' aviation...

[Nightmare]

Actually it could be 360 feet tall, hence add 1360 feet to get LSALT. Unless the highest point in the area happens to already be a structure of greater than 360 feet, in which case you just add 1000 feet.

It could be 860 feet, as the minimum 1000 feet applies to flight over built up areas, in rural areas the minimum is 500 feet

[ian00798]

It could be 860 feet, as the minimum 1000 feet applies to flight over built up areas, in rural areas the minimum is 500 feet

When developing an IFR LSALT as this thread is about you have to be a minimum of 1000ft above any obstacles (except during an instrument approach) so the 500 ft rule does not apply, that is regarding low flying not LSALT

 

 

[Nightmare]

When developing an IFR LSALT as this thread is about you have to be a minimum of 1000ft above any obstacles (except during an instrument approach) so the 500 ft rule does not apply, that is regarding low flying not LSALT

It's not necessarily a IFR related question from the OP, it was a question about OzRunways. In VFR, you can have LSALT's at 860ft AGL. Sometimes necessary when navigating around restricted and controlled airspace

[ian00798]

It's not necessarily a IFR related question from the OP, it was a question about OzRunways. In VFR, you can have LSALT's at 860ft AGL. Sometimes necessary when navigating around restricted and controlled airspace

Then that isn't an LSALT, that's just operating your aircraft in accordance with CAR157. Given that AIP specifically states that the lowest LSALT in Australian airspace is 1500ft I think it is reasonable to say that 860ft can not be considered an LSALT. I really strongly recommend giving AIP GEN page 18 a read, it outlines this pretty clearly by AIP standards

 

 

[ben87r]

LSALT MSA MORA etc have no meaning when VFR (day). There are altitudes that a pilot may consider to the his lowest safe altitude but it isn't LSALT.

 

 

[Nightmare]

I guess the term in VFR is "VFR Safety Height" as described in DH's Cross Country Endorsement Manual, where you find the highest points 10nm left and right along your track, and add 1000ft or 500ft, as appropriate, plus the obstacle clearance of 360ft. This figure is also the one you may(it is optional) input into the LSALT column on the Flight Notification Form.

 

All through my XC training, my instructor and I were referring to this Safety height process as LSALT.

 

After re-reading the manual, I see that you are correct, LSALT is IFR, Safety Height is VFR, both use the LSALT column.

 

Thanks for pointing this out to me.

 

 

[ian00798]

No worries mate, nobody in this business knows everything, and it got you back in the books to solidify a previous concept and then at the time learn something new, all in all a win I would say.

 

 

[ben87r]

For a normal VFR flight 500' agl can be held (judged) and that half the fun of VFR, it's much more flexible. IFR doesn't allow as much flexibility (fun), if on a 'cruise' sector it would be prudent to go as high as the sector length/ aircraft performance would allow, but this is mission dependent. I still love (and can't do) flying 500' costal, it's about as good as it gets.

 

 

[Nightmare]

For a normal VFR flight 500' agl can be held (judged) and that half the fun of VFR, ....I still love (and can't do) flying 500' costal, it's about as good as it gets.

A friend of mine, offered to take me for a fly yesterday in his RV6, and we did just that along the Gold Coast near Q1

We were at 1000ft in this photo, but going the other way we were at 500ft. As you say, it's about as good as it gets!

 

 

[Awqward]

In the US and in the UK the 500' rule only applies to people, vessels, vehicles and structures....you can fly all day at 10' along a deserted beach....now that is fun...