DC9/MD80/737 Airstairs: The forgotten ones

DC9/MD80/737 Airstairs

The forgotten ones

By Greg Napert

September 2000

There was a time when the image of a passenger aircraft pulling up to a small terminal and deploying a futuristic-looking set of stairs was a common sight at an airport. For corporate and general aviation aircraft, it still is. But as passenger terminals developed and terminal Jetways and mobile stairways became commonplace; the need for airstairs became greatly diminished.
Aircraft such as the DC9, MD80, MD90, and 737 aircraft have had a long enough history that many of them were built with the forward passenger air stair assembly. As the need for them was reduced, later models were produced without forward airstairs. Many aircraft were also converted to non-airstair versions Ñ a 200+ lb. weight savings for the operator.
Regardless of the history, there continues to be a need for airstairs for specific operations. Freight operators, corporate conversions, and newer corporate variations of these aircraft such as the 717 still find air stair installations a necessity. The result is that there is still a need for maintenance and repair knowledge, replacement parts and qualified sources for overhaul.

Basic airstair description
The airstair installation, with some variations from aircraft to aircraft, includes four main components:
1. Forward and aft rail assembly
2. Carriage assembly
3. Electrical installations
4. Airstair assembly
The airstair assembly and the airstair door are powered with 115/200 VAC, 400 Hz, 3-phase power source located on the aircraft. The airstair installation and the airstair door may also be operated with a power source of 24 to 28 VDC.
Airstair assembly consists of two rigid beams connected to the ladder assembly, which also consists of the steps, hand-rails, lights, and wheels that allow the airstairs to seat firmly on the ground when extended. This is what extends from the carriage assembly to the ground for entering or exiting the aircraft.

Servicing airstairs
Light bulbs below each stair tread should be checked frequently and replaced, if necessary.

One of the few facilities in the country that offer air stair overhaul services is Professional Aircraft Accessories. According to Joe Gramzinski, Chief Inspector for Professional Aircraft Accessories in Titusville, FL, "We have been servicing, repairing and overhauling airstairs that are installed on various aircraft including the DC-9, MD-80, MD-90, along with the 717 and 737 for over 10 years. Although some aspects of the overhaul can be a challenge, we can usually overhaul a standard airstair assembly within 30 days. This includes installing it on our universal test stand, this will allow us to give it a operational check and a complete visual inspection prior to teardown."
Of the many challenges related to overhauling some of this seldom used and often abused equipment, corrosion is a major factor in determining the overhaul requirements. Airstairs are exposed to the elements and experience a considerable amount of cracking due to widely varying stress and weight loads on the steps.

The process
Billy McLean, Shop Supervisor for PAA explains that the overhaul process can be somewhat involved, but it is interesting to note the wide variety of conditions that some of these stairs are in. "Most stairs we receive don't even operate when we place them on the test stand."
McLean explains the overhaul process starts with an incoming inspection and test to establish the received condition of the unit.
Next, the cover is removed and the stairs are removed, and the carriage assembly will be detached thus allowing further inspection and component removal from these assemblies. The actuator assembly will be removed and overhauled separately per the manufacturer's overhaul manual. The stairs are quite big and bulky in size so these are disassembled in sections as needed. The carriage assembly will also be disassembled, cleaned, inspected, chains and sprockets replaced if needed, cam followers, etc.
Intergranular corrosion can result in cracking and deterioration of airstair assemble. Inspec carefully for signs of corrosion. Field repairs must be evaluated according to overhaul manual and supporting documentation