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We present the study of the X2-class flare which occurred on the 27 October2014 and was observed with the Interface Region Imaging Spectrograph (IRIS) andthe EUV Imaging Spectrometer (EIS) on board the Hinode satellite. Thanks to thehigh cadence and spatial resolution of the IRIS and EIS instruments, we areable to compare simultaneous observations of the \xxi~1354.08~\AA~and\xxiii~263.77~\AA~high temperature emission ($\gtrsim$ 10~MK) in the flareribbon during the chromospheric evaporation phase. We find that IRIS observescompletely blue-shifted \xxi~line profiles, up to 200 km s$^{-1}$ during therise phase of the flare, indicating that the site of the plasma upflows isresolved by IRIS. In contrast, the \xxiii~line is often asymmetric, which weinterpret as being due to the lower spatial resolution of EIS. Temperatureestimates from SDO/AIA and Hinode/XRT show that hot emission (log($T$)[K] $>$7.2) is first concentrated at the footpoints before filling the loops. Densitysensitive lines from IRIS and EIS give electron number density estimates of$\gtrsim$~10$^{12}$~cm$^{-3}$ in the transition region lines and10$^{10}$~cm$^{-3}$ in the coronal lines during the impulsive phase. In orderto compare the observational results against theoretical predictions, we haverun a simulation of a flare loop undergoing heating using the HYDRAD 1D hydrocode. We find that the simulated plasma parameters are close to the observedvalues which are obtained with IRIS, Hinode and AIA. These results support anelectron beam heating model rather than a purely thermal conduction model asthe driving mechanism for this flare.

Simultaneous IRIS and Hinode/EIS observations and modelling of the 27 October 2014 X 2.0 class flare