If you use a wheelchair you will transfer twice when boarding. One from your wheelchair to the aisle chair, the second from the aisle chair to your aircraft seat. Generally it will be the airport assistance team, and not cabin crew that will assist you.
At boarding you will be offered a transfer chair similar to the Columbia Transfer chair. Because this chair needs to take you down the aisle of the aircraft it is very narrow. If you or your travelling partner experience spasms you may want to consider a means of preventing arms from getting hurt when proceeding backwards down the aisle.
If you need help transferring from your wheelchair to the transfer chair The Promove sling provides a more comfortable and dignified solution. It is quick and simple to use, when transferring by hoist is not an option it is available at some airports. Some airports use more basic sling straps to lift passengers into their seats. Some airports use these, other passengers bring their own. If you are concerned about transferring we recommend booking an assessment at Tryb4ufly to try before your flight. Transfer boards are also used.
Most European airlines provide seats that can supports you as you navigate down the aisle to the toilet, similar to the Air+Chair.