High-Pressure Gas Cylinder Inspections

There are misunderstandings surrounding the inspection requirements for high-pressure gas cylinders used as part of aircraft standard and supplementary systems.


There seem to be misunderstandings surrounding the inspection requirements for high-pressure gas cylinders used as part of aircraft standard and supplementary systems. We would like to discuss where the inspection and maintenance requirements come from and what recent changes the government has made relative to those requirements. Maintenance of high-pressure gas cylinders has been a confusing issue for a long time and rightly so since it is not very clearly addressed either by the manufacturers or the FAA.

In August 2002, the Department of Transportation (DOT) issued new regulations covering the handling of hazardous materials including the use and testing of high-pressure gas cylinders for the purpose of transporting hazardous materials. We will discuss the new regulation in depth, but first a look at how the lesser-known DOT regulations fit into the aircraft inspection and maintenance requirements set forth by the FAA.

We are taught that it is the manufacturer and the aircraft’s type certificate data sheet that drive all of our inspection and maintenance requirements. Let’s briefly review what makes up the inspection and maintenance requirements for an aircraft.

Airworthiness

First of all, aircraft inspection and maintenance requirements are designed with one primary purpose, to ensure the aircraft’s continued airworthiness. Although the definition of airworthiness is not specifically contained in the regulations, it can be found on the aircraft airworthiness certificate. “Airworthiness” is defined as “conforms to type design and is in a condition for safe operation.” When we as maintenance technicians 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” means conforming to how that aircraft was originally built and configured, i.e. how the engines are installed, the way the structure is put together, how the equipment is installed, the configuration of the interior, etc. The type certificate also defines and/or refers to “Airworthiness Limitations” for that aircraft. These limitations are contained either in the type certificate itself or in another FAA approved document referred to by that 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., and in some cases, the structural inspections of critical safety of flight components on the aircraft. The list is as different for each aircraft and its engines as the type certificate itself. In addition, aircraft that are altered from their original type design are considered to have received a “major alteration.” Major alterations must be accomplished in accordance with data that has been FAA approved (STC, field approval, etc.). The data used to support a major alteration may also contain its own “Airworthiness Limitations” that must be adhered to.

The “condition for safe operation” portion of the definition of airworthiness 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 (relative to maintenance) tell us where to find the inspection requirements for an aircraft, like what to inspect and maintain and at what frequencies, while the maintenance rules tell us where to find information on how to perform inspections and maintenance on an aircraft as well as record the maintenance.

Inspection and testing requirements

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