I'm in a similar situation to you. I went on a plane before when I was younger, and loved it. But since then I developed really bad anxiety and suffered psychosis and agoraphobia. Then last year my friend asked me to go on holiday with her and I said yes. I was going out at this point, and feeling a bit better. I was travelling a bit, which was very hard, but she suffered anxiety sometimes too so we supported each other. I was so nervous about the plane. I took rescue remedy which you can buy in most supermarkets or chemists. It helps a bit but at the end of the day you are still going to walk onto the plane feeling very scared. Really frightened people can try and get the seat at the front where there's loads of leg room so you don't feel trapped in.
Have you booked your flight? I personally would try and make sure I was flying on a big plane- one of those mega jumbos! I've found that the smaller ones make you feel more vulnerable and if the plane turns you feel it more. Turbulence has never been a problem for me. It's way over hyped. Occasionally you feel a slight weightless as you go through a cloud or something but I doubt you'll experience anything bad.
The take off is the worst bit if you're scared, although if you like driving in a car and accelerating you might enjoy it- I did the first time. If not, know what's going to happen because that helps you prepare a way of coping:
The plane will just trundle around for a bit waiting for the all-clear and lining itself up on the run way. You'll be like 'is it taking off, is this it?' but it always takes a while. When it's time to go suddenly it feels like the whole plane is coming alive, the engines become quite loud and there's a high pitched buzzing sound of all the electrics. I always close my ears! Clench your tummy and close your eyes, and you can always pull down the shutter on the window so you don't see everything whizzing by. The plane will the accelerate. It's very rapid, no gradual build up, and it feels a lot faster than a car, but as soon as the wheels leave the ground you lose the sense of going really fast. Put it this way- the faster it goes the faster you get there!
A few seconds after the plane leaves the ground you will feel a strange sensation as though something is pushing your head down. That's just air pressure. It soon stops. The plane is up in the clouds before you know it, and then it's just a case of keeping calm until it starts to descend. The pilot will usually introduce themselves, tell you the weather, the times etc, and they'll tell you how high up you and when you start descending.

I have to admit the first time for me was horrible because of my anxiety, and when it was time to repeat the experience on the way home I was petrified, but second time round it was actually better. If you do things your mind learns. Even if you hated it the first time, somehow having experienced it makes you calmer. At the end of the day just remember the anxiety can't hurt you.

Lastly, I know it doesn't sound very responsible to advise drugs, but I find diazepam REALLY helps if I'm panicking. When you've been anxious for a while you go into this dreamy, frightened state and it can very hard to calm down. There is nothing like taking one of these when you've been in a state. It makes you feel like you did when you were a child and nothing frightened you much. All the anxiety just comes out of your muscles and you feel 'real' again. If I fly again I'm going to beg my doctor for these, otherwise I will find someone else who takes them to give me a couple!The more you take the more you need to take though and they can leave you a bit dependent.

You have to try and stop the anxious ruminating you're doing now, otherwise you are just heading for disaster. You'll be imagining the worst and panicking for 15 months and then you'll be anticipating it so much that when you step on the plane you'll have a massive panic. It doesn't have to be that way. Be one step ahead of your fears and you'll be ok.
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Three months is not long enough for therapy to work - I took anti- depressants for one year and saw a cognitive therapist for 18 months in order to overcome my travel phobia and panic attacks.

Unfortunately this isn't a quick fix but I stopped the c.t 5 years ago and haven't had an attack since.

She did give me a relaxation tape, which included various exercises to lower stress and muscle tension, to use on planes and this along with the extra medication they gave me worked wonders.
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I have and always will, hate flying. I have to read and imagine I am on a train! May sound a bit silly, but it really works for me. I have always been told it is safer to fly than to drive a car and I must admit, as a driver, it is probably true. I have flown every year for the past 6yrs and everytime, it seems to get easier. Imagine you are on a train. You will be fine. x
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Its not a quick fix in my experience, all you can do is mask it in the short term. I have tried everything to make flying more comfortable and am getting their. I have tried
Valium - get some it may help you, but take high doses
Alcohol - my preferred option, ok if you can control yourself
Hypnotherapy - works with alcohol
Flight therapy course- go on one if you get the chance it will help

Like I say in the short term choose your poison. but looking ahead try and address it using therapy techniques and by confronting it.
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I know you said you've had therapy, but I know someone who was quite similar to you, completely terrified of flying, got panic attacks etc.
She had hypnotherapy, and has never been scared since.
I don't know whether that was the type of therapy you had, but if it wasn't, I suppose it might be worth a try?
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Take some sleeping tablets when on the plane
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You could try Emotional Freedom Technique. I've been using it on my anxiety and depression and it has helped me a lot.
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http://www.emofree.com
http://www.sarah-holland.co.uk/howto.html</br>

As both an airline captain and licensed therapist, I've treated over 7,000 clients for fear of flying. This has led to major advances in treatment, and made it possible to help anyone and everyone fly.

Few psychologists and psychiatrists are trained to deal effectively with fear of flying. Instead, they attempt treatment with Cognitive Behavioral Therapy, relaxation techniques, or medication.

Medication. Research shows medication helps prior to the flight but causes increased distress during the flight itself.

Relaxation. Few fear of flying suffers will find relaxation techniques adequate. Once feelings start, relaxation offers no help.

CBT. Distress begins milliseconds after being triggered by noise or turbulence, and quickly escalates to high anxiety or panic. CBT cannot keep distress from starting. Being word-based and thought-based,CBT is far too slow to keep up.

Having dedicated twenty-eight years to the development of advanced help for fear of flying, both as an airline captain and a licensed therapist, I've found the solution is to keep distress from starting.

Protection to combat distress must be established prior to flight. Protection must operate so quickly that distress is stopped before it becomes conscious. In other words, for protection to work, it must operate automatically and unconsciously.

Information on how fear of flying can be combated effectively is available in the free library at www.fearofflying.com/wordpress/