Well here is another one. Again one that will never affect me.
I see that the airlines going across the North Atlantic follow a single track the whole way across. This makes sense – nothing much is going to change, traffic wise, across the Atlantic, so ATC just set them up and and let them fly and then ATC on the other side takes them off the track after crossing.
I’m assuming that they are out of VHG range for ATC. Is that correct?
Do they use HF to coordinate with ATC?
If not, what do they do if they want to change their level or change track? For example if there is a lot of turbulence at a particular level or there is a thunderstorm on their track? Do they just sort it out amount themselves with whoever is within VFR range / on TCAS? Use HF to get a clearance? Sat phone to get a clearance? Or am I incorrect and VHF comms to ATC is available at airliner altitudes across the North Atlantic?
Thank you.
@dublinpilot, try watching some of the KLM videos, they describe what happens – ACARS is used (satellite one, not the VDL), so the crew could request a new clearance if needed, also ACARS automatically reports the position as well.
dublinpilot wrote:
Do they use HF to coordinate with ATC?
If not, what do they do if they want to change their level or change track? For example if there is a lot of turbulence at a particular level or there is a thunderstorm on their track? Do they just sort it out amount themselves with whoever is within VFR range / on TCAS? Use HF to get a clearance? Sat phone to get a clearance? Or am I incorrect and VHF comms to ATC is available at airliner altitudes across the North Atlantic?
Historically they have been using HF. AFAIK this is still required but now satellite communications is also used. An interesting thing is that aircrew don’t communicate directly with ATC but with a ground radio operator who relays messages to and from ATC. That’s why the FIR in the Northeastern Atlantic is called the “Shanwick Oceanic FIR”. The radio station is in Shannon, while ATC is in Prestwick.
There are contingency procedures in place if they have to change level and/or track without having time to get an ATC clearance. Separation between the tracks is pretty large so there’s plenty of room.
This communication problem in oceanic airspace is a reason why ICAO is launching “Performance-Base Communications”. That is similar in concept to Performance-Based Navigation in that it doesn’t specify any particular technical solution but only the “performance” of any chosen solution. In the case of PBN the navigation accuracy is the main factor, in the case of PBC it is the time it takes to exchange a message. E.g. RCP 240 – “Required Communication Performance 240 seconds.”
Thank you both! Another one cleared up 
I also recall NATS publishing some Iridium satphone numbers for this and other purposes.
I’m assuming that they are out of VHG range for ATC. Is that correct?
- Yes, albeit some tracks (either daily published ones or random routes filed by airlines) are within VHF coverage
Do they use HF to coordinate with ATC?
- Very rarely. It is all done by text messages via CPDLC. Still, for every FIR a HF radio check is done and listening watch maintained (SELCAL).
If not, what do they do if they want to change their level or change track?
- Try to obtain a clearance using CPDLC
For example if there is a lot of turbulence at a particular level or there is a thunderstorm on their track?
- Short notice for WX go off track and when deviating to the north, descend 300ft, and vv.
- Very rare but when there is a pack of planes one can talk with each other to sort it out additionally to first trying for a reclearance via CPDCL/HF and following the contingency.
I also recall NATS publishing some Iridium satphone numbers for this and other purposes
All as Snoopy mentions 
CPDLC as #1
VHF worked (and probably still works) pretty good at altitude.
Sat phone used as last resort…
Re need to alter course, procedures are published (headings, offset flying, etc), all the stuff one learns when starting flying long haul…
dublinpilot wrote:
If you were flying something like an F15 or F22 with very high performance, would receiving a clearance “No speed restriction” actually allow you to go supersonic? Or does the 250kts below FL100 still apply and do you need a specific clearance to go supersonic?
There are two kinds of speed restrictions:
SERA mandated restrictions, e.g. 250 kt below FL100 in airspace classes C (VFR) or D and E
ATC mandated restrictions – not only by explicit instruction but also. a general speed limit e.g. of 250 kt for IFR below FL100 in a class C TMA.
“No speed restriction” only lifts the second kind – not the first one.
I’m confused by this. Could you rephrase? Does it depend on IFR vs VFR? Let’s say I want to do a legal 300kts low approach at a controlled airfield, how would that work?
HBadger wrote:
I’m confused by this. Could you rephrase? Does it depend on IFR vs VFR? Let’s say I want to do a legal 300kts low approach at a controlled airfield, how would that work?
For class C it depends on IFR vs. VFR as IFR is separated for all other flights (no speed limit) while VFR flights are not separated from each other (thus speed limit).
Let’s say I want to do a legal 300kts low approach at a controlled airfield, how would that work?
A 300 kt low approach in classes A-C (IFR) or B (VFR) is legal with ATC approval.
