AerBabe has covered some key points. They'll be looking for evidence that you have made a contribution to knowledge; PhD requires original contribution and MPhil requires significant contribution. Since the expert in the room is yourself, you'll be expected to answer with the evidence supporting your contribution. Since you're on airworthiness and flight test techniques, lets try a typical question and what they are looking for (forgive me if I know nothing about your topic - that doesn't stop me being an examiner).
"in your thesis, you discussed how changes to the present flight test techniques would give a more structured approach to the flight testing of the aircraft structural engineering - surely flight testing has developed over the years to cover that fairly well - didn't the Americans develop this at Pasadena in the 70s?"
This question is loaded with multiple openings and questions - in your answer, you MUST BE ABLE TO state what your contribution is [I actually showed that ........] ; REFERENCE that to the latest developments in the field [flight testing of the aircraft structural engineering was based on ABC until recently and this is still the method used at Cranfield] ; DISPLAY knowledge of the background to the field [actually at Pasadena they did XYZ, but since then . . . .].
The next question will ask you to discuss your methods, your data collection process, and/or the way you analysed it. They are not trying to teach you how to suck eggs, but rather to see that you have mastered the issues. So a calm restatement of your method is adequate when they start to probe. When they say for example "do you think you should have analysed that using ANOVA to eliminate the bias . . . . ." then simply restate why you did what you did 'the regression was adequate to show the relationships, and I tested the statistics to make sure that they were significant'.
I would get a colleague to ask you some questions about your thesis - that will get you into the technique of rapidly collating your thoughts to give an answer which may draw on several chapters of work. And relax - the examiners aren't trying to fail you - they are trying to pass you and make sure that it was really you that did the work. If your professor has allowed your work to go forward, then it has already passed as meeting the grade
