"Mk5a coaches are not the first new rolling stock to be introduced into the UK. Look back at almost all new trains introductions and you'll find stock that was fraught with issues and problems. This stock is generally (now) very good and as has been mentioned, the actual number of breakdowns in service has been minimal. I note your comment of the length of time these trains have been developed and tested. It may interest you to know that out of the new Nova fleets, Class 802 has so far demonstrated a higher failure rate than the Mk5a coaches. Remembering that the AT300 design is extensively tested and is currently used by three operators with over 100 units accepted, maybe you could explain your argument for why brand new stock should not encounter teething issues?