Can someone explain why HMS Illustrious is being sent to Gibraltar aeroplaneless?
Because...
1. It is not being sent to Gibraltar, it is passing Gibraltar en-route to the Middle East to take part in the long-planned Exercise Cougar '13,
and...
2. It is not "aeroplaneless" as it is now a helicopter carrier and will have several helicopters embarked in order to carry out its role in Ex Cougar '13, i.e. to assist in the delivery of hundreds of Royal Marines ashore and provide ASW screen to the 'task force'.
Good enough explanation for you?