Last month we started working through the new Special Inspection Documents that were added to the latest revision of the 100 Series Service Manual. This month is a continuation of the SIDs review. This is not intended as a comprehensive review but rather just some notes and highlights of the individual SIDs.
SID 32-20-01 Nose Gear Torque Link Bolt and Fork Inspection
Type of Inspection – Visual and Eddy Current
Initial Compliance:3000 hours or 5 years
Recurring Compliance: 3000 hours or 5 years
Approximate Labor Time – 2 hours
I used to feel the nose gear was a weak link in the Cessna single engine airframe design. The fact that the very first CPA Tech Note is about nose gear shimmy seemed to support the thought as well. I now believe the reality is the nose gear just incurs so much stress and strain that it just doesn’t have a chance.
We have frequently removed the nose gear scissors looking for the source of free play and find bent bolts. It’s so expected we just keep a good supply of these bolts in stock. The upper torque link is a different matter.
When the strut fully extends, there is a block mounted on the upper torque link that acts as the extension limit. The stop block also forces the nose gear to lock in the center position when the strut extends in flight. Unfortunately, the geometry of the upper torque link and its stop block put a large bending force at the middle of the link. It’s not a matter of if, but when the link will bend.
As the link bends, the strut will extend farther than it is designed to. On the non-retractable gear planes, like our 182, the bending of the link isn’t really the problem. The real concern is when the bend becomes a break. There is a snap ring that “should” keep the strut from departing the airplane, but there’s nothing that will steer the nose gear.
You can see the protrusion on the forward end of the upper torque link. As the strut extents and the scissors straighten out, the protrusion makes contact with the a flat spot on the strut causing the nose gear to center
Assuming the strut stays with the plane, the strut will stay centered as long as it is extended. All bets are off once the strut compresses after landing. There’ll be no directional control, no hint which way it will turn, no idea how far it will turn, and absolutely no indication to the pilot that any of this is about to happen.
One alternative to the cost of having the eddy current testing performed on the upper link is to replace the part. If a crack is found, you’ll have to replace it anyway. New links are available from Cessna from $1,281.00 to $1,841, depending on the aircraft serial number. One could expect to pay about 40% of list price for a serviceable part on the used market.
SID 53-11-01 Carry-thru Structure Corrosion Inspection
Type of Inspection – Visual
Initial Compliance: 10 or 20 years depending on environment
Recurring Compliance: 5 or 10 years depending environment
Approximate Labor Time – 6 hours
Inspection of the wing attachment carry-thrus is an operation CPA has been encouraging for years. It’s one that should already be a part of every annual inspection by a Cessna knowledgeable inspector.
Corrosion in the top of the cabin is a long known issue on our Cessnas. As the planes sit in storage, atmospheric changes create a certain “green house” effect that sends moisture and other chemicals from the upholstery to the bare aluminum in the top of the cabin. We’d also like to inspect inside each of the carry-thru channels, but there’s no easy access without removing a wing.
This is a rare example of a very clean wing spar aft carry through channel
The actual inspection time is pretty short, but proper viewing may require removal of the headliner. On most planes, the age and frailty of the headliner can turn a routine event into a more expensive upholstery job.
SID 53-12-02 Fuselage Forward Doorpost Inspection
Type of Inspection – Visual
Initial Compliance: 4000 hours or 10 years
Recurring Compliance:1000 hours or 3 years
Approximate Labor Time – 1 hour +
This inspection requires some effort to see all the areas in question. The area around the wing strut attach points are very critical, and any defect will warrant immediate action.
The + on the labor for this SID is because the inspection likely leads to a modification as recommended in SEB95-19. SEB95-19 calls for installation of service kit SK182-115 which includes enlarging several floor access holes, then installing some pretty major structural enhancements to the forward door post bulkheads at the lift strut attachment area.
We’ve not found any cracks in these areas yet, but it will eventually happen. Installation of SK182-115 is a pretty major event, and we’ll give a detailed accounting of the first one we do. SK172-147 is the same reinforcement kit for the 172 series and SK210-156 applies to the strutted wing 210 series.
This is a view of a very clean wing spar forward carry through and its attachment to the forward door post
SID 53-30-01 Fuselage Interior Skin Panels Corrosion Inspection
Type of Inspection : visual and possibly ultrasonic
Initial Compliance: 10 to 20 years depending on usage
Recurring Compliance: 5 to 10 years depending on usage
Approximate Labor Time: Lots
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