Aircraft Engine Manufacturers. Aircraft Engine Repair, Modification and Overhaul. Aircraft Electrical Systems. If you focus on this you will be in demand. Aircraft Fuel Systems.
Every aircraft has one and it needs to be repaired.
Aircraft Hydraulic and Pneumatic Systems. If you even have an inkling in this area, it is a good idea to focus on it. Aircraft Ground Support Equipment. Christian Missionary Aviation. Aircraft Instrument Manufacture, Repair and Overhaul.