Airline transport operations are carried out in a wide range of visual and instrument meteorological conditions. For all but the most limiting of degraded visibility situations, however, the pilot can choose to land the aircraft manually, using the visual cues available through the cockpit windshield. The answer to the question - how is this achieved, which gives the paper its title, tau flare or ... [Show full abstract] not tau flare ? - may seem rather obvious but has actually challenged researchers for some time. The optical flow theory of visual perception offers solutions in terms of the way pilots pick up motion from the surfaces over which they move. In a relatively recent incarnation, flow theory transforms motion into the temporal, time-to-contact parameter tau, defined as the time to close on a surface at current closure rate. Research conducted at Liverpool has applied this theory to low-level helicopter flight. The present paper builds upon this work and reports on the application of the theory to fixed wing aircraft during approach and landing. Using data from piloted flight simulation experiments, the results show how tau-guidance strategies exist for the flare and touchdown manoeuvre in terms of the rate of change of the tau of height above the runway surface and in terms of coupling the tau of height above the runway surface with a general intrinsic tau- guide. Furthermore, it is shown that the values of the rate of change of tau with time, tau- dot, and the coupling constant selected by the pilot, directly influence the acceptability of the touchdown rate achieved. The introduction of a degraded visual environment is shown, under certain circumstances, to cause a breakdown in the tau relationships observed. Potential uses of these results are presented in terms of application to future pilot vision aids, which is the planned next stage of this work. Such displays may work in one of two ways or indeed, a combination of both: the first is a display to command a specific tau relationship that the pilot must follow; the second is a display that provides an indirect mechanism to allow the pilot to couple onto an appropriate tau guidance mechanism for the flare. Application of this work to the fields of flight safety and flight training is also briefly discussed.