At least eight people have died after a helicopter with 16 people on board crashed into the North Sea.
The Bond Super Puma came down about 15 miles off Peterhead on the Aberdeenshire coast, at about 1400 BST.
The crashed helicopter was returning from BP's Miller field, 168 miles north east of Aberdeen.
Readers have been contacting the BBC News website to share their comments and thoughts. Here is a selection of your emails.
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My husband works offshore. I hope they find them all safe and sound. BP are a very good company and health and safety are the main object. Thinking of them all and their families too
Sharon Povey, Bristol
I just returned home from offshore yesterday after being stuck for a day when we had to make an emergency landing on a platform due to oil leaking from the gearbox. If the pilots hadn't been so professional we wouldn't have made it back. I just hope someone has survived this.
Graham Strachan, Laurencekirk, Aberdeenshire
I really feel for what has happened and my thoughts are with the families. I work offshore myself and I have noticed that if the helicopter was to crash when in full flight flying at 2,000 feet, chances of survival would be minimal. I have been involved in an incident where the helicopter nearly ditched. Is it not about time that these helicopter companies adjust their flight plans and helicopters to allow lower flying to increase chance of survivals in future incidents?
Innes Commander, East Kilbride, South Lanarkshire
As the daughter of the engineer who worked on the Bristow Super Puma that crashed in 1992 off Shetland and a close friend of the pilot and co-pilot (one of whom died) of that doomed flight, my deepest sympathies and understanding go to the families of those who have died and are missing and those friends and workmates at Bond that are mourning the loss and picking up the pieces. I know what you are all going through and am thinking of you all.
Lives just lost in Newfoundland, such a tragedy, now another in Scotland. As part of the "offshore family" it really hits home. My husband works off the coast of Aberdeen and I understand the dangers involved all around, but what is wrong with these helicopters? My thoughts and prayers go out to all.
Mary Ann Cameron, Sherbrooke, Nova Scotia, Canada
Firstly our prayers are for all involved in such a tragedy. Although the statisticians will start quoting the numbers of North Sea helicopter flights per year and incidents, the facts are helicopter flights are six times more risky than fixed wing flights and flying in North Sea weather conditions compounds these risks. Investments should be made in providing a large passenger transporting vessel with helideck facilities large enough to allow Puma and other 14+ passenger capacity to shuttle shorter distances from close proximity of the fields.
Patrick Costigan, Moscow, Russia
This is the second Bond helicopter to go down in as many months. About time for a full investigation into Bond's operations and maintenance schedules.
D. Bowles, Bury St Edmunds
I want to pay tribute to the professional individuals who execute the north seas mission. Aviation is hazardous, but it is how you deal with crisis that differentiates companies. You can't eliminate the threat of technical failure, but comfort must be taken from the professionalism of the north crews.
Roddy Dennis, UK
We, as a small community, just three weeks ago experienced this same tragedy, when 17 of our friends lost their lives when a Sikorsky 92 helicopter they were on crashed into the North Atlantic going to an oil platform. May you find strength in friends and family at this most sudden and difficult time. May God be with you.
Dave Flower, Marystown, Newfoundland, Canada
I work for a North Sea operator and one thing has particularly struck me about this tragedy. All personnel travelling offshore North Sea used to carry locator beacons so that they could very quickly be found in the water if a helicopter ditched. Our company uses new beacons but apparently the older type used by BP (and used by the people who ditched at Etap) caused interference with the helicopters own emergency system. As a precaution, the old beacons were taken out of service by some of the major companies. I dread to think that the people who ended up in the sea this afternoon were not able to be found because they didn't have the correct equipment.
I myself work offshore in the North Sea and I don't like having to be on these helicopters as I know this happens more often than I would like it to but unfortunately it's a risk you have to take in this job. When this happens I think I speak for all the guys when you feel a great sadness for all those involved. My thoughts, as well as my colleagues' here, go out to the victims and their families of today's tragic helicopter crash. I only hope something can be learned from this to try and help prevent it from happening again.
Paul Stewart, Aberdeen