DC9/MD80/737 Airstairs: The forgotten ones

The forward and aft rails along with the handrails must also be disassembled, cleaned, inspected, parts and cables replaced if needed.
After all of these assemblies have been serviced and repaired, they will all be primed and painted (if applicable). New non-skid material is replaced on the stair steps. This material is simply a stick-on adhesive that is pressed in position and then sealed with a sealant around the edges. This sealant prevents the non-skid material from pealing and prevents water from getting under and causing corrosion.
The unit is then assembled completely to the manufacturer's specifications for final testing and rigging, then shipped to the customers worldwide for installation onto their aircraft or on their shelf as inventory.

Real life
According to McLean, "There aren't a long list of mandatory parts that have to be replaced at each overhaul, but there are a few. There are also some components that we have to NDI as well, but for the most part, this is not a 'safety of flight' component, so there are not many critical inspections."
Much of the rebuild simply involves a great deal of degreasing, cleaning, scraping and repainting. It's a great deal of physical labor "elbow grease" that's required. You also need the proper tools to do a good job. An airstair stand is used at PAA to duplicate the mounting studs that are on the aircraft installation. The stand simulates the exact height of the aircraft so as to be able to test whether it's adjusting properly to meet the ground.
Darryl Stazenski, Inspector for PAA, says "There are certain areas that are problematic in terms of cracking or corrosion and we look at those areas with a bit more discretion. We often find field repairs that are questionable. We also see good repairs, but these have to be inspected especially close to be sure they conform to the overhaul manual."
McLean adds, "Unfortunately, the biggest problems surrounding repair/overhaul of these airstairs is lack of parts support and repair information, and the high price tag for replacement parts. Additionally, some of the lower level assembly parts aren't available. The result is that instead of being able to replace a small stud or piece of simple hardware, we're forced to purchase an entire assembly of related parts."
A good example is of studs that are positioned on the lower tray assembly that are bonded to the composite structure. These studs could easily be repaired by performing a bit of composite work, but the studs aren't available, so if you have a damaged stud, you've got to replace the entire lower tray assembly. "There is no data available from Douglas/ Boeing to make this repair, so we're stuck with this scenario in several instances. What operators choose to do in some of these cases is salvage components from other serviceable stairs. This is often a much more cost-effective solution, but it is not always available," he explains.
McLean says that one thing that can hold up an overhaul is missing components that were removed from the stairs by the operator and not turned in for overhaul. "We usually call the customer to ask if they have the part, and if they do, they either have to send it to us to inspect so we can sign off the overhaul, or make a record of the fact that the customer is holding the part. If that happens, we will approve all repairs with the exception of that component."
One example of a component that can be problematic is the round access panel on the lower tray. This panel is a fiberglass cover piece of round aluminum, and many customers don't ship it with the stairs. "Unfortunately, if it is lost, we can't manufacture another, and a new one costs over $6,000 to replace," explains McLean. "Yet another is the locking mechanism (hooks) that is used to hold the stairway in place when the stairs are fully extended. These hooks can cost over $3,000 to replace."
In terms of the airstair actuator mechanism, McLean says, "We have occasionally replaced the chains and sprockets, but they are normally in pretty good condition. They have a tensioner on them that accounts for a considerable amount of wear. You can usually tell when they are stretched beyond limits due to the carriage binding and when adjustments are difficult to make. The chains are actually one of the more rugged components in the system, however. More than likely, a good cleaning, inspection, and lubrication are all that's required for these components in order to return it to service."