at speed. The Rail Accident Investigation Branch (RAIB) report determined that the incident was probably caused by a sequence of events which would not have been possible with a traditional manually-operated mechanical door: a combination of a piece of dirt incorporated in the door lock switch during manufacture and a software bug in the door control system allowed the door to remain unlocked after the train called at Luton, but prevented this condition being detected. Deflation and inflation of the pneumatic door seals, initiated automatically by detectors responding to the train stopping and starting at subsequent stations, then gradually prised the door out of its socket until at a point north of Kettering it became able to open. This condition was detected and an automatic brake application initiated, whereupon the inertial forces caused the door to slide open fully; however the indications presented in the driver's cab were ambiguous and were interpreted as caused by faulty systems, and he, therefore, cancelled the brake application. The train was finally halted at Desborough summit after a passenger reported that the door was open. On 20 February 2010, unit 222005 working 1F45 14:55 London to Sheffield derailed near East Langton, Leicestershire. Two wheels on Coach E in the middle of the train came off the track; on approaching the site of the derailment the train was travelling at close to 100 mph. No other wheels derailed and the train remained upright. There were also reports that one or more road vehicles on an adjacent highway were struck and damaged by debris as the derailed train passed. 222005 was moved from the site the next day after a replacement bogie was fitted and was for a few months formed of vehicles of 222101 and 222022 including a standard class cab end which was temporarily renumbered until the damaged vehicles were returned to the set in mid-June. The derailment caused damage to the Midland Main Line near Kibworth for a distance of two miles, the line underwent emergency repairs by Network Rail to get the stretch of line back open for start of service on 24 February 2010. The RAIB investigated the incident and found that it was caused by a complete fracture of the axle, due to a bearing stiffening to the point where it would no longer rotate properly. The RAIB recommended that a review of gearbox and axle design be undertaken, and