The June 2011 eruption of Cordón Caulle was the first major hemispheric-scale ash cloud event in the Southern Hemisphere since 1991, and the first since the creation of the International Airways Volcano Watch. Coming just over a year since Eyjafjallajökull, the eruption served to bring a sharp focus to the issue of dealing with 'old ash' that was nevertheless still 'visible'. On its first circuit of the globe in mid-June, southern Australia had diffuse parts of the cloud linger for several days, while the main body of ash moved over New Zealand in the jet stream. Subsequently, a deep low pressure system on 21 June brought the dissipating, but still clearly visible, ash over all the major cities of Southeastern Australia, to the intense frustration of airlines and passengers. The Darwin VAAC used a strongly evidence-based approach to issuance of advisories, based on the assumption that ash observed by pilots or on geostationary satellite imagery could be fairly called 'visible ash'. Pilot reports were actively solicited through embedded meteorological units in two major airlines and in Australia's National Operations Centre. In some instances this actually resulted in a more conservative approach to what would otherwise have been the case, as pilots proved to be very sensitive to the presence of ash at altitudes below where the main body of ash was expected to be. The sensitivity of the MTSAT geostationary satellite was also extraordinary due to the nature of the ash and the geometry of the event. In general terms, the event was operationally far easier than a tropical eruption to handle due to far better observations. Post-event debriefs have focused on the information flow during the event and how decision-making is influenced. Despite major efforts to keep airlines well briefed, one of the strongest comments made was that a higher flow of actual observations such as remote sensing results and comparison to pilot observations would serve to increase confidence in the VAAC products, as some airlines were still under the mistaken impression that VAACs lean heavily on model output without reference to observations in their ash analysis. An enhanced information flow may have affected decisions worth many millions of dollars. The easy collation and communication of observations and other relevant information is therefore a key priority in the future development of the International Airways Volcano Watch.