SPECIAL BOLTS
TDD: The bolts are special because they are 64th inch oversize on the standard AGS diameters. This allows for reaming the exisiting bolt holes and hopefully taking out all the nasty little cracks which have already started to form by the time 114 FI is reached. The reaming also makes sure that the exisiting holes in the spar and the newly drilled holes in the reinforcing straps are in perfect alignment. Failure to use the right bolts and the right techniques will invalidate the subsequent fatigue testing which was carried out after the fatigue test specimen was repaired by embodiment of the modification; it will jeopardise the future ultimate life of 200 FI if the mod is not done correctly. The answer to getting the cost down is to run a programme of say ten aircraft at a time, which will make it economic to produce runs of reinforcement plates and fasteners. Also, the learning curve of doing what is a serious dockyard job can be spread over the whole batch of aircraft; the turnround time will also drop sharply as the team gains experience. This job is not one to be tackled by every M3 on a little airstrip doing just one aircraft.
To pick up an earlier post, there are no Bulldogs without a fatigue life limitation to when modification BH193 must be carried out. The ex-RAF ones still using a fatigue meter can run to 114 FI, which can exceed as much as 10,000 hours if the aircraft is flown carefully. However, all the rest (ie, those without a fatigue meter) are lifed very much on the safe side at 5,000 hours before the modification must be carried out. All Bulldogs - ex-RAF or not - then encounter a tailplane attachment limitation at 15,000 hours, but that is far enough down the pike not to be a concern at the moment. In answer to Meon Valley Flyer, the real problem with the spar is that during the full scale fatigue test it bust. Therefore, not doing modification BH193 is not an option for Bulldog owners if they want to fly (safely) beyound 5,000 hours (or 114 FI on an ex-RAF aircraft).