weather avoidance during oceanic crossings
 

What is your experience with weather avoidance during oceanic crossings, say in poor HF coverage?
Do you usually get clearance in time - and what procedures have helped you?

thanks

You divert while you obtain clearance.
Contingency procedures exist (climb/descend).

Most modern airliners nowadays have Datalink (CPDLC) so receiving a clearance in the NAT HLA to divert around weather is not an issue. Been a long time since I was forced to use HF comms. However, you should make all attempts to receive a clearance prior to the event. If unable, then as SAFELIFE has stated you are authorised to follow the Contingency procedure for weather avoidance, whilst still attempting to receive a clearance.

I’ve had to do quite a lot of deviation over the years, some of it authorised. You could be on a track system, airway or random route and each has their own subtleties - have a look through your OM C and country regulations for the particular chunk of airspace.

If there’s a nasty bit of weather which you think would be unsafe to fly through, then you’re going to go around it. Next thing is to tell those affected by your decision and if you can’t get through to ATC then broadcasts on 121.5 and any chat frequencies should be received by anyone near enough to be a problem, a bit like the IFBP in parts of Africa. TCAS is not a replacement for proper separation but it sure helps; putting all the lights on wouldn’t be a bad idea, either.

The one thing you don't do is fly through the weather because you're trying to get clearance. It's happened. As Safelife mentioned you use the contingency procedures while awaiting clearance or if the clearance is denied. I've never had to use the contingency procedure on the NATS. One time the deviation clearance came about 2 miles prior to the buffer limit as we were deviating on a heading that would exceed the buffer limit. For some reason the controller wasn't answering the CPDLC request even though we requested the deviation with at least 10 minutes prior notice. Approaching the weather we tried via SATCOM and the phone is answered in an office not co-located with the controller. So the person answering the phone said he'd walk over the control room and advise the controller that we were trying to contact him. In the meantime we needed to start deviating. Just prior to reaching the offset limit the clearance came through on CPDLC. New FO with maybe 1-2 months line experience asked how many times I've had to do this - no CPDLC reply from the controller, use the SATCOM to try and talk with the controller directly, start a deviation without clearance, etc, etc, all in an attempt to deviate on the NATS? "Never. It's YOU." New people are jinxed!

You will, of course, all now be familiar with the latest weather deviation procedures in NAT Doc 007, which requires the +/-300ft change from the cleared FL to be initiated when the divergence off track (without a formal clearance) reaches 5nm or more, vice the `old` 10nm.

There You go

You request more than you need and request it well in advance knowing that sometimes you actually won't have to use it(although it is only requested if something is out there that is a potential problem). That way you have the clearance in hand and can use it without delay which sometimes happens. Of course once past the potential problem with no more potential problems in sight, report Back on Track once you are back on track. Otherwise, you can easily find yourself getting closer and closer to the weather while you are waiting for what are sometimes relatively long delays for the clearance to deviate.

If denied a deviation, make a free text to ATC asking if the deviation might be available at a different altitude.