  A fraction of the XMM-Newton/EPIC FOV is obscured by the dysfunctional (i.e.
bad) pixels. The fraction varies between different EPIC instruments in a given
observation. These complications affect the analysis of extended X-ray sources
observed with XMM-Newton/EPIC and the consequent scientific interpretation of
the results. For example, the accuracy of the widely used cosmological probe of
the gas mass of clusters of galaxies depends on the accuracy of the procedure
of removing the obscuration effect from the measured flux. The Science Analysis
Software (SAS) includes an option for recovering the lost fraction of the flux
measured by a primary instrument by utilising a supplementary image of the same
source. The correction may be accurate if the supplementary image is minimally
obscured at the locations of the bad pixels of the primary instrument. This can
be achieved e.g. by using the observation-based MOS2 image for correcting the
pn flux, or by using a synthetic model image. By utilising a sample of 27
galaxy cluster observations we evaluated the accuracy of the recovery method
based on observed images, as implemented in SAS 18.0.0. We found that the
accuracy of the recovered total flux in the 0.5-7.0 keV band in the full
geometric area within the central r = 6 arcmin is better than 0.1% on average
while in some individual cases the recovered flux may be uncertain by ~1%.
