Low Level Grid Point Wind and Temperature Chart Data Format
Thread Starter
Low Level Grid Point Wind and Temperature Chart Data Format
Is anyone able to provide a reasonable explanation as to why the LL GPWT data format uses:
- 2 digits for wind direction, and
- 3 digits for wind speed?
All wind directions can be intuitively described with 3 digits, even if the leading digit is zero. I can generally grasp where a forecast wind of 030 or 090 is coming from.
But how often is a forecast low level wind in excess of 99 knots? The occasional cyclone involves low level winds in excess of 99 knots, but I generally don’t fly if the low level winds are forecast to be in excess of .... hmmmm.... I’ll pluck 75 knots. Makes things unpleasant, I guess.
Smart enough to remember that 9999 means in excess of 10KMs visibility. I reckon I have enough brain cells left to remember that a forecast wind of ‘99’ means in excess of 99 knots.
I note that all current LL GPWTs at the time of this post have a ‘0’ in the front of every forecast wind direction.
What awful and dangerous risks to aviation safety would arise if the LL GPWT format was:
- 3 digits for wind direction
- 2 digits for wind speed (with the rule that ‘99’ means in excess of 100 knots).
I realise my question assumes that someone’s reading LL GPWTs, and that that’s an heroic assumption. But humour me.
It might be the ICAO compliant format. I wonder where low level winds are routinely in excess of 99 knots...
- 2 digits for wind direction, and
- 3 digits for wind speed?
All wind directions can be intuitively described with 3 digits, even if the leading digit is zero. I can generally grasp where a forecast wind of 030 or 090 is coming from.
But how often is a forecast low level wind in excess of 99 knots? The occasional cyclone involves low level winds in excess of 99 knots, but I generally don’t fly if the low level winds are forecast to be in excess of .... hmmmm.... I’ll pluck 75 knots. Makes things unpleasant, I guess.
Smart enough to remember that 9999 means in excess of 10KMs visibility. I reckon I have enough brain cells left to remember that a forecast wind of ‘99’ means in excess of 99 knots.
I note that all current LL GPWTs at the time of this post have a ‘0’ in the front of every forecast wind direction.
What awful and dangerous risks to aviation safety would arise if the LL GPWT format was:
- 3 digits for wind direction
- 2 digits for wind speed (with the rule that ‘99’ means in excess of 100 knots).
I realise my question assumes that someone’s reading LL GPWTs, and that that’s an heroic assumption. But humour me.
It might be the ICAO compliant format. I wonder where low level winds are routinely in excess of 99 knots...
Have to agree. I’ve seen a few students transpose wind speed and direction with the new format. Clearly whoever designed this was not a pilot, nor did they consult a pilot.
Thread Starter
That solves at least one mystery for me, Cloudee: Student pilots (at least some of them) are being required to interpret LL GPWT charts. I feel for them.
How on Earth do they work out the grids to be used for a flight? My EFB now (mercifully) plots the plan on the electronic copy of the GPWT and does some ‘automatic’ calculations, but .... jeeez ... I’d hate to be doing it the ‘old fashioned way’ on these ‘new’ charts.
How on Earth do they work out the grids to be used for a flight? My EFB now (mercifully) plots the plan on the electronic copy of the GPWT and does some ‘automatic’ calculations, but .... jeeez ... I’d hate to be doing it the ‘old fashioned way’ on these ‘new’ charts.
2 digits, 3 digits...
Probably commonality with the the upper level charts.
Heres a question, a tangent from the topic but on a similar path. Why not name runways with 3 digits? Runway 26 is 260 degrees....
Probably commonality with the the upper level charts.
Heres a question, a tangent from the topic but on a similar path. Why not name runways with 3 digits? Runway 26 is 260 degrees....
Thread Starter
I asked about the safety risk...
Runway numbers? What do they do in the USA?
Aviation seems to be unique in the propensity to come up with counter-intuitive systems. 2 (or even 1) digit to describe the magnetic orientation of a runway (or wind direction), yet 3 digits to describe a wind speed that, at low level, is almost never above 99 knots.
What could possibly go wrong?
Runway numbers? What do they do in the USA?
Aviation seems to be unique in the propensity to come up with counter-intuitive systems. 2 (or even 1) digit to describe the magnetic orientation of a runway (or wind direction), yet 3 digits to describe a wind speed that, at low level, is almost never above 99 knots.
What could possibly go wrong?
At Melbourne the east-west runway is 263 degrees but is called RWY27. Answers on a postcard......
Thread Starter
Thus demonstrating, once again, why using single or double digits to describe runway or wind direction, while using three digits to describe low level wind speed, is a patent and confusing nonsense.
But what could possibly go wrong.
But what could possibly go wrong.
Dropping the third digit for the direction doesn't lose you anything whereas dropping the third digit for the speed might leave you severely disappointed when the headwind is 150kts rather than 99kts.
Last edited by le Pingouin; 29th May 2018 at 16:23.
The numbers for the runway are just a name, not a bearing to fly to land - that's what eyeballs and instrument approaches are for. The new runway at Melbourne (when it eventually gets built) won't actually be quite parallel with the existing east-west runway - when departing to the west the centrelines converge by a few degrees.
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We’re talking about low level forecasts.
Thread Starter
Here’s another stupid idea:
- 3 digit wind directions
- whatever number of digits the winds happen to be.
Compatability with high level GRIB would be the go. But...caculate wind drift using two digit direction can be as much as ten degrees out...as in 34 can mean 336 to 344...going to be fun ace-ing nav with such coarse information
The reason for such coarse course data is obvious.....not many high flying fast movers use compass and clock to enable pilotage.
edit...I know some arent on high salary but steerage takes it a little too far
edit...I know some arent on high salary but steerage takes it a little too far
Last edited by OZBUSDRIVER; 29th May 2018 at 22:06.
The wind is forecast to the nearest 10 degrees, so if you switched it around you’d have the same situation anyway.
Every 3 figure direction value would have a zero at the end, instead of every speed value having a zero at the beginning.
This is is a big fat waste of time.
Every 3 figure direction value would have a zero at the end, instead of every speed value having a zero at the beginning.
This is is a big fat waste of time.
Thread Starter
A big fat waste of time, except for people like Cloudee’s students who transpose counter-intuitive numbers.
But we get it loud and clear: It’s not about reducing the risk of mistakes. It’s about the convenience of the ‘service’ provider.
But we get it loud and clear: It’s not about reducing the risk of mistakes. It’s about the convenience of the ‘service’ provider.
That makes sense. “They” being bureaucrats and “need” being their convenience. It goes without saying that they don’t give two ****s about GA down low.
I personally only use the GPWT for an overview. The wind/temp profile function in NAIPS is handy when doing a manual flight plan for a long leg. Gives you an expected head or tailwind component with no maths required.