High-pressure Gas Cylinders: Maintenance requirements

High-Pressure Gas Cylinders Maintenance requirements Joe Hertzler All new parts installed during the maintenance function have to be manufactured to one of the quality standards of 14 CFR Part 21.303. There are many misconceptions about...

High-Pressure Gas Cylinders

Maintenance requirements

Joe Hertzler
Joe Hertzler

There are many misconceptions about maintenance requirements for high-pressure gas cylinders. This month we will discuss where the requirements come from and what has changed over the past few months. Maintenance of high-pressure gas cylinders has been a confusing issue for a long time and rightly so since it isn’t clearly addressed by the manufacturers or the FAA.

In August of 2002, the Department of Transportation issued new regulations covering the handling of hazardous materials including the use and testing of high-pressure gas cylinders to transport hazardous materials. We will discuss the new regulation in depth but first let’s talk about how these lesser known DOT regulations fit into aircraft maintenance and inspection requirements.

It can be a bit confusing since we are taught that it is the manufacturer and the aircraft’s type certificate data sheet that drives all of our maintenance requirements. Let’s review what makes up the maintenance requirements for an aircraft.

To begin with “airworthiness” is defined as “conforms to type design and is in a condition for safe operation.” Although this definition is not specifically contained in the regulations, it is found on the aircraft airworthiness certificate. When we as maintenance people make a statement that an aircraft or the maintenance we have performed is airworthy we are saying that the aircraft or the piece of the aircraft maintained conforms to its original or properly altered (STC, field approval, etc.) type design.

“Conforming to type design” is about how that aircraft was built and configured, i.e., the engines installed, the way the structure is put together, the equipment installed, the configuration of the interior, etc. The type certificate also defines what is called Airworthiness Limitations. These limitations are either contained in the type certificate itself or in another FAA approved document referred to by the type certificate data sheet. The airworthiness limitations consist of specific time change requirements for parts that are critical to the safe operation of the aircraft, i.e. engine components, landing gear components, specific bolts, etc. The list is different for each aircraft and its engines.

Inspection and testing
The “condition for safe operation” part, however, means just what it says, the condition of the aircraft. In order to keep the aircraft in top condition we are required to inspect and maintain the aircraft in accordance with the regulations contained in operational rules Part 91, 135, 121, etc. and maintenance rules Part 43. The operational rules spell out the inspection requirements like methods and frequencies and the maintenance rules define how to perform inspections and maintain an aircraft.

Now how do we get to the inspection and testing requirements for gas cylinders? Well, the type design of an aircraft may include certain cylinders installed in the aircraft as equipment. For example, cylinders for crew and passenger oxygen, cylinders that contain pressurized gas as a secondary means to extend or “blow down” the retractable landing gear, and cylinders that carry fire extinguishing agents for engine fires and cabin fires.

Manual vs. AD vs. SB
The aircraft manufacturer is responsible for issuing a maintenance manual as well as an inspection program for the aircraft. In general, the maintenance manual will include some reference to the Title 49 CFR inspection requirements for these cylinders, however, these cylinders are one case where the maintenance manual does not hold the final authority for what maintenance to perform and when to perform it. The final authority is really traced back to Title 49 CFR, the basis of the maintenance manual requirement. More specifically, the new Title 49 CFR Part 180.

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