Most aircrafts' fuselages are made of aluminum. There is a trend recently that aluminum is being replaced by carbon fiber (CF) to reduce weight. The weak electromagnetic shielding effectiveness (SE) for CF becomes, however, a big issue, as long as lightning protection is concerned. When an aircraft is hit by a lightning, there will be a much higher electric burst in cable harness compared to aluminum fuselage. This paper shows the simulation results which confirm the big difference by comparing the CF fuselage with the aluminium one. The simulation is carried out with a transient solver of CST CABLE STUDIO, - a full-wave electromagnetic simulation code.