Yes. Use the HF anytime you'd normally use VHF but can't because you're out of range.
Be aware that Flightwatch are a messenger service, they can't give you clearances and traffic information directly, they just relay that information from the relevant centre controller. This means it can take time to get what you need. Don't call for a clearance and expect to get it in the next breath, it may take several minutes.
Also be aware that the Flightwatch guys monitor several different frequencies spread over a large area. Don't get annoyed if they don't respond to you straight away even if you can't hear any other activity on frequency. They are probably busy on a different frequency.
Make sure you tell them what frequency you're transmitting on. They can't respond to you if they don't know what frequency you came through on.
When contacting them, try the frequency you were given by centre or if you didn't get one, go for a higher frequency during the day and lower at night (each area has three frequencies to choose from). Wait at least 30 seconds before calling again if you get no response and try two or three times on one frequency before trying another.
Be aware that they may be booming through nice and clearly to you but you might not be to them. Also they have several transmitter sites to choose from. If you can't hear them very well, tell them and they'll probably try a different transmitter. A big clue that a change of transmitters will fix things is if you hear them clearly talking to another aircraft but when they talk to you you can't hear them clearly.
Try not to give them, or ask for, unnecessary information. HF comms are a pain in the arse so use it to get the minimum of information you need to conduct your flight safely, no more. For example, if you're on the ground and need to file a plan, use a phone, don't clog up the Flightwatch frequency with it. All common curtesy type stuff really.
Last edited by AerocatS2A; 10th Jul 2012 at 10:54.