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.


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, oxygen cylinders for crew and passengers, 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. The aircraft manufacturer is responsible for issuing a maintenance manual as well as an inspection and maintenance 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 aircraft manufacturer’s maintenance manual requirement. More specifically, the new Title 49 CFR Part 180.

Title 49 CFR Part 180

The reason Title 49 CFR Part 180 takes precedence over the maintenance manual is because it is the actual regulation rather than an FAA accepted maintenance manual. An example of a regulatory vs. manufacturer maintenance requirement relationship more familiar to us is the relationship between an aircraft inspection program and an Airworthiness Directive (AD).

A specific example is that of the nose landing gear fork inspection requirements for the Raytheon Super King Air B200. The inspection program for the King Air was once at a frequency interval of 150 hours. A problem was found in specific part number nose gear forks and the FAA issued an AD requiring an inspection each 150 hours until the part was replaced. The inspection is to be performed in accordance with a service bulletin, also calling the inspection out at 150 hours. A few years later Raytheon revised the inspection program and extended the look-phase inspection frequency to 200 hours. Shortly thereafter the service bulletin calling for the nose gear fork inspection was extended to 200 hours as well. The problem is, the AD continues to refer to the original revision of the service bulletin (in this case Revision III) and continues to require the inspection be performed each 150 hours. Now logic might say that the manufacturer has analyzed the situation and determined that a less frequent inspection is adequate to maintain a high level of safety and through issuance of the revised service bulletin has authorized the interval of the inspection to be extended. This however is not the case. Why? Because ADs are regulatory and accepted maintenance manuals and service bulletins are not.

Whenever a new AD is issued it is issued as an amendment to 14 CFR Part 39. So in the case of the King Air nose gear fork inspection, until the AD is revised, the applicable forks must be inspected at 150 hours.

The DOT regulation found in 49 CFR Part 180 governing the inspection, testing, and replacement of cylinders is really the higher authority over the aircraft manufacturer’s maintenance manual. There are, however, a couple of ways that an operator might have a different inspection requirement than that contained in Title 49 CFR for gas cylinders. The manufacturer of the aircraft could place the requirement for inspections testing and replacement of cylinders in an FAA approved Airworthiness Limitation section of a maintenance manual, or in any other FAA approved maintenance requirement such as an air carrier’s operation specification. In those cases, the FAA is very careful to make reference to Title 49 CFR in an effort to keep the requirements the same. If by chance the requirements contained in an FAA approved document such as an Airworthiness Limitations section of a maintenance manual or an Air Carrier Operation Specification are in conflict with those requirements contained in 49 CFR Part 180, the most restrictive requirement must be applied.

Now for the Title 49 change. The DOT issued final ruling on, Aug. 8, 2002 covering the inspection, testing, and replacement of cylinders, however, many are still not aware of the change. The change to Title 49 reorganized and moved the cylinder requirements from the old familiar 173.34 to

180.205 — General requirements for re-qualification of cylinders;

180.209 — Requirements for re-qualification of specification cylinders; and

180.213 — Re-qualification markings.

These new regulations can be found in various places on the Internet. Although there was no substantial change to the requirements contained in the new rule, the new organization makes reading and determining the requirements for cylinders manufactured to DOT specifications much easier.

New rule Following is an outline of the new rule:

For our purposes, cylinder inspection requirements include all cylinders used to transport compressed gas in aircraft.

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