Our Sioux, XT131, has had an interesting winter period to say the least! She was due a Primary Service (annual inspection) and some NDT (Non-Destructive Testing). We also found some unexpected issues along the way, which is not unusual when playing with aircraft, certainly of this vintage (just like our engineers).
A Primary is quite a detailed series of inspections, checks and lubrication tasks. The methods used for conventional NDT include visual testing, penetrant testing, magnetic testing, ultrasonic testing, radiographic testing and eddy current testing, but all share common features in that the materials under test are not harmed in any way. We had to strip the Sioux so we could remove the engine frame and tail rotor blades for testing. So, a great winter had begun.
During the Primary we decided to replace the engine mag plug housing as it has been leaking (when the mag plug is removed) for a few years. On removal, we found a large shard of metal wedged in the plug housing. We believe the metal was from the Freewheel so an investigation was started. During the strip and examine, one of the freewheel springs had a piece missing which matched the shard found. However, further examination of the lower planetary gear drive revealed some of the plastic bearing cages had disintegrated, resulting in the rubbing together of some roller bearings. At this stage, we decided a gearbox replacement was the only option.
So all complete and we have a serviceable Sioux? Oh, but no. We completed a 30 minute ground run after the gearbox change – all well. But, back in the hangar and a fuel leak from the main fuel supply pipe! So, we have to find a pipe and then complete a 3 yearly full flight test. Watch this space for more news…