The popularity of multicarrier systems such as orthogonal frequency division multiplexing (OFDM) is based on the ability to cancel inter-symbol-interference (ISI) and channel distortion using a single tap equalizer in the case of a stationary channel. In doubly selective fading channels OFDM transceivers are unable to diagonalize the channel matrix and consequently inter carrier interference (ICI) appears. The discrete fractional Fourier transform (FrFT) has been suggested to enhance performance over traditional OFDM systems when transmitting over doubly-dispersive channels. In this paper a novel hybrid multicarrier system based on the Fractional Fourier transform and Fourier transform is presented. Taking advantage of these properties, we propose an adaptive transmission in those channels using multimode transmission of FrFT-OFDM and FT-OFDM, and evaluate its performances through computer simulations.