Data link "No comm"

[voske 36]

On my flight from OMDB to KSEA I tried to request wind data on the ROUTE DATA page, but "DATA LINK NO COMM" was displayed on the ROUTE DATA page. 

 

According to FCOM2 11.34.3 the status message "NO COMM" occurs when

- the VHF and SATCOM data radios are operational but not available

- the VHF data radio has failed and the SATCOM data radio is not available, or

- the SATCOM data radio has failed and the VHF data radio is not available.

 

As I attempted to request wind data between 85N18 and 80N23, my assumption would be that VHF data radio nor SATCOM data radio is available above a certain latitude. Is that correct?

[downscc 1,327]

I think ARINC is on the IMMARSAT geosynchronous birds, which are parked over the equator. At extreme latitudes there is a limit to coverage, just not sure what that is. Above 80 deg seems reasonable, imagine trying to look at something over the equator from the poles... even if it is 22000 mi above the Earth it is still a very low angle above the horizon.  You'd be on the HF for sure.  GPS birds are low Earth non-synchronous orbits and as long as you have enough of them in sight latitude doesn't matter.

 

I've used the satellite data below 75N, didn't know the range limitation was simulated...interesting.

 

Just curious, at 85N you were still using ETOPS180??

 

EDIT:  Quick trig approximation suggests that the satellite would be less than 10 deg above the horizon, yeah that's pretty low.

[voske 36]

Thanks for the info! Makes sense now.

 

I was trying to use ETOPS180, but that didn't work out in PFPX, so I switched to ETOPS207. The flight plan was a RW flight plan I found on http://www.edi-gla.co.uk/ Route:

N0493F330 DAVMO Y601 GABKO Q4 ASMET/N0485F350 Q4 RIKOP/K0891F350 B114 ASB B434 MAXAT A370 URG A299 OSGAN/K0883F360 A299 TINRI/K0887F370 G359 BELEG/K0890F360 G359 ADERA/K0886F380 G359 ABERI/M083F380 85N118W 80N123W 75N124W/M083F390 70N123W 65N122W/N0470F390 60N121W YXJ J534 STAHL/N0471F410 J534 YWL/N0473F400 T618 YYJ/1353

 

Enroute alternates were UBBB, ENBO, PAFA and CYEG.

[Budbud 227]

 

 

As I attempted to request wind data between 85N18 and 80N23, my assumption would be that VHF data radio nor SATCOM data radio is available above a certain latitude. Is that correct?

 

Hi,

 

I'm not sure for aviation, but in the Merchant navy where we use Inmarsat for communications as well as emergencies, it is not guaranteed to work properly beyond latitudes over 76deg N/S (5deg elevation above the horizon).

 

You may get a few degrees of latitude extra due to the aircraft altitude but I'm not surprise that the communication would be lost above 80deg.