I had mentioned this in one of the existing threads regarding Live Weather upper winds always showing 225 degrees at 3 knots in many parts of the world.
As most know, the upper winds do not appear to work at all when an aircraft is positioned in US airspace, do appear to work reliably in Europe most of the time, and can be hit-or-miss in other regions.
While doing a long distance flight in the A320 from Acapulco, Mexico to Los Angeles, I noted that upper winds were working perfectly on departure from MMAA and during initial climb, and suddenly stopped working on the flight northbound, somewhere south of the latitude of Manzanillo (MMZO).
This point is still hundreds of miles south of US airspace.
Earlier this week, I decided to set up a test flight at lower altitude in the G-1000 Cessna 172 to see if I could determine a specific location where the Live Weather upper winds stop working, and was successful. I have now repeated this test flight 4 times, on 4 different days, and have found the upper winds cease working at a precise location every single time.
I will give the details of how I performed this test in case anyone else would like to try it to see if they get the same results.
With LIve Weather enabled, load the G-1000 Cessna 172 on the threshold of runway 26 at MMZH (Ixtapa-Zihuantanejo airport) on the Pacific Coast of Mexico.
There is no need to create a flight plan - just select runway 26 as your departure point.
If Live Weather is working, you will most likely see at least some clouds, as they are quite common at this location at this time of year. On my 4 test flights I have had clouds ranging from one scattered layer to multi-layer broken and overcast.
On the pilot’s G-1000 screen, enable the display of wind, and select “Option 3” which gives the most detailed readout of wind direction and velocity. Also enable the display of the DME readout for the number one NAV receiver.
Tune the number one NAV receiver to 113.8, which is the ZIH VOR, located at the west end of the airport.
Set the CDI to VOR 1 mode (green needles), and preselect a course of 292 degrees, This outbound radial is low-altitude airway V1, and after takeoff, you will intercept the radial notrhbound, heading towards Manzanillo.
Set your altitude selector to 8000 feet. This will insure sufficient altitude to clear the coastal mountain range to the north.
Every time I have loaded at this airport, I have always had “genuine” Live Weather winds at the surface. The velocity is usually quite light, which is normal for this part of Mexico in late summer assuming no thunderstorms or hurricanes are in the vicinity. On my flight today the surface wind was 283 degrees at between 4 and 5 knots.
Once airborne, be prepared to intercept the outbound 292 degree radial from ZIH VOR, as it will come up quickly. Once established on the 292 radial, with the CDI needle centered, engage NAV mode on the autopilot to track it northbound. I normally climb to my cruise altitude of 8000 feet in VS mode.
The winds on my flight today were quite similar to previous flights. As I climbed, the wind gradually turned clockwise from the original 283 degrees at the surface, to between 320 and 330 degrees at 8000 feet. Both the wind direction and velocity varied slightly with the speed ranging between 2 and 6 knots at various points in the flight .
The “failure point” of the Live Weather wind injection occurs at 93 DME miles north of the ZIH VOR. The wind quit working at this exact location on each of my 4 test flights. The aircraft will give a slight “lurch” at this point, as the wind direction goes instantly to 225 degrees, and the velocity to 3 knots.
On my first test flight, I continued flying another 100 miles northbound to see if the wind would return, but it never did.
On the next three flights (including today), I flew 3 miles past the point where the wind quit working, did a 180 degree turn, re-centered the CDI needle and began flying back toward ZIH.
The wind injection started working again at exactly the same point where it originally quit when heading north: 93 DME from ZIH, on the 292 degree radial. Passing this point southbound, the aircraft again gave a small lurch, and the wind slowly came back from 225 degrees to the original 320 degrees, and the velocity went to 5 knots.
NO other Live Weather features change at the moment the wind drops out or returns. The clouds do not change, nor does the temperature or barometric pressure.
I’m not sure what is significant about this particular location. It might mark the boundary between two adjacent cells in the MeteoBlue atmosphere model, or perhaps the specific latitude or longitude of the point has something to do with it. In any event, this point is still well south of the United States border, so the wind problem is not unique only to US airspace.