  We use the localized principle component analysis to detect deviations from
scale invariance of the primordial power spectrum of curvature perturbations.
With the technique we make uncorrelated estimates of the primordial power
spectrum with five wavenumber bins. In the framework of a minimal LCDM model,
using the latest cosmic microwave background data from the WMAP and ACT
experiments we find that more than 95% of the preferred models are incompatible
with the assumption of scale-invariance, but still compatible with a power-law
primordial spectrum. We also forecast the sensitivity and constraints
achievable by the Planck experiment by performing Monte Carlo studies on
simulated data. Planck could significantly improve the constraints on the
primordial power spectrum, especially at small scales by roughly a factor of 4.
