James Shuttleworth is absolutely right on this point, and a lot of the rush to air brake was either inspired by paranoia amongst those who did not understand the regulations, or those who saw commercial advantage in the promotion of fitting air brakes. There are hardly any of the steam lcomotives which have been fitted with air brakes, which have not suffered an air brake related failure at some point, some more than one, and there have been several instances of rough shunts when coupling up due to the inherent time lag when using the air brake valve on certain vac fitted engines. The complexity of some of these systems has to be seen to be believed, in the case of the GWR engines which have been fitted it just about doubles the amount of pipework and valves - Total - on the engines, and one in particular is an abomination, both in access and appearance terms with very little thought applied either to location of equipment or to the visual impact of fitting the system. Compared to the air equipment, the original GWR equipment is far more robust and reliable (worth noting that most of the commentary elsewhere on this website about GWR vac brakes results from poor maintenance and a complete lack of comprehension of how the system works). Anyone proposing the fitment of air brakes to the exclusion of vacuum should perhaps compare the figures for vacuum brake failures against those for air brake failures on steam locos. That is if you can find a vac brake failure. There is also an urban myth about recovery of vac brake trains. With the scarcity of spare diesels, a situation made worse by the allocation of large numbers of loco's to weekend engineering works, you only have to look at the B1 problem at Hutton Cranswick when it took about 5 hours to find an air braked diesel to rescue the train, to see that recovery is a problem full stop whether air or vac. Note what James says about operator's responsibilities. The plain fact is that Vacuum is simpler, is far more easily and cheaply maintained to the required standards, and as long as the RSSB and the HMRI are happy with the braking performance, there is no reason to displace vacuum. It does need to be remembered that the brake force on a Vac Mark 2 is basically identical to an air braked one as most of the brake gear underneath is identical, with only the arrangement of cylinders and levers differing. At the speeds which steam is permitted to run, given the installation of TPWS and the almost total installation of modern signalling systems nation-wide there is no technical reason for the rather unreasoned prejudice against vacuum that appears to exist in certain quarters. It really comes down to who you want to operate with. If you are happy to go with West Coast then there is no need for air braking a loco. If however you wish to work with EWS at some time or other, then you will have to fit air, and it might just be advisable to examine the costs of fitting and maintaining an air brake sytem, and dividing the cost of it by the number of trips which you might expect to be able to do in the next ten years before making that decision. You may just be surprised at how much per trip your decision to work with EWS will add to the amount which you need to charge for your daily hire fees!