  The flyby anomaly is the unexpected variation of the asymptotic
post-encounter velocity of a spacecraft with respect to the pre-encounter
velocity as it performs a slingshot manoeuvre. This effect has been detected
in, at least, six flybys of the Earth but it has not appeared in other recent
flybys. In order to find a pattern in these, apparently contradictory, data
several phenomenological formulas have been proposed but all have failed to
predict a new result in agreement with the observations. In this paper we use a
multivariate dimensional analysis approach to propose a fitting of the data in
terms of the local parameters at perigee, as it would occur if this anomaly
comes from an unknown fifth force with latitude dependence. Under this
assumption, we estimate the range of this force around 300 km.
