Did this twice - once for an internship, another time for the graduate programme. As soon as you turn up you're sat down with the other candidates and it's clear from the get go that Rolls Royce only choose the extremely high calibre - I was meeting people with 3 internships under their belt, probably the highest calibre group of engineering students I'd ever met... so in hindsight I'm not sure how I ended up at the assessment centre and I felt like I didn't really stand a chance. But oh well, still gave it my best shot. You then meet the assessors and have a chat with them prior to the competency interviews starting, so it's first impressions from the very start!
Competency interview - 1 hour long. Starts off with a 10 minute presentation about yourself (you are informed of this when receiving your assessment day offer) - who you are, what your skills are and how you'd 'add value' to your role within Rolls Royce. Most people have one interviewer, I happened to have two. Next the interviewer will probably have a relaxed chat with you, talking about points you made in your presentation and going over your CV. My first experience they ripped my CV to shreds - my second experience, they didn't even have my CV infront of them and it wasn't mentioned! Then come the generic STAR based competency questions.
Numerical tests again but on paper. Exactly the same as the online ones.
Then there's the group task - 1 hour long. Split into two teams of 6. If I remember correctly there was an assessor watching each individual candidate. My first time, the team had to design a marble run out of paper and cardboard to get one coloured marble to the end of the run before the other, and you have to decide as a group to buy 'supplies' such as scissors and tape with a budget. Both teams failed, but they're more assessing how you work within a team, time keeping skills, etc. My second time, we had to design and 'manufacture' six identical paper planes to a business brief for a fictional airline company, once again buying 'supplies'. The planes had to fly six feet and once again both teams failed. At the end of each task they ask you to present your ideas to the room as a group with no real time to prepare, so be ready to expect that. Assessors may ask questions such as 'what would you do differently, what went well?' etc.
Then is a 45 minute buffet lunch - no time to relax, you'll be eating and drinking standing up with the assessors (have fun balancing your meal whilst trying to converse with the assessors with a half full mouth of curly fries).
Second interview - technical. 1 hour. One interviewer. Started off with the interviewer asking about my technical interests and experience, where my expertise lie, my strengths, my weaknesses, etc. Then according to this, he/she will ask you questions based on the area of engineering you want to go into. I was given the luxury of choosing my topic of questions (Stress Analysis and FEA), but I heard from someone else that after they explained their interests, the interviewer thought it'd be nice to ask them questions completely different to their area of expertise. The interviewer guides you through the questions, showing you diagrams along the way and asking you to interpret them. They're trying to analyse how you work through problems and approach new technical situations, so don't be worried if you don't know the answer. In my first experience I was given a picture of a gas turbine engine, asked to identify some critical components and then the interviewer walked me through a problem of a sensor going wrong in the turbine, how will I identify the problem? How will I check for errors? What variables could be affecting the problem (pressure, temperature, etc)? Then they give you a choice of engineering topics to talk about in 'layman terms' for ten minutes, which is literally you talking to their face about an area of engineering for ten whole minutes whilst they sit in silence... which was pretty weird. I chose microstructure. Trying to assess your communication skills and ability to articulate technical knowledge maybe? Who knows. Overall the technical interview was a much better and more relaxed experience than I was expecting.
An exhausting but rewarding experience - 7 hours straight of not letting your guard down, so get a good nights sleep before. There's quite a lot of time spent sitting around waiting for the next stage - in this time we had two grads come speak to us to do a sort of FAQ session which was interesting and useful.
Very efficient process overall, found out that I'd been rejected the next day. But they give you phone feedback which is appreciated, even if it was pretty vague and not very useful - the general feedback for me was 'you had a great positive day, you did really well... but not well enough'. Meh... back to writing soul destroying online applications for me I guess