Can MS flareless fittings be used on aircraft?

Flareless fittings, such as MS flareless fittings, are not permitted for use on aircraft systems that handle fluid lines carrying fuel, hydraulic fluid, or other critical fluids. This restriction is due to the stringent safety standards and reliability requirements in aviation. Aircraft must utilize fittings that provide a secure and leak-proof connection, and flareless fittings do not meet the necessary criteria for high-stress and high-pressure environments typically encountered in aviation.

The use of MS flareless fittings in aircraft could lead to issues such as leaks or failure due to vibration, temperature changes, or pressure fluctuations that are common during flight operations. Aircraft designs are rigorously tested and specified by manufacturers, who rely on fittings that have been proven to operate safely under the conditions specific to aviation.

Regarding the other options, stating that flareless fittings can be used "always," "only on small aircraft," or contingent on limited manufacturer specifications would not adhere to the comprehensive regulations and standards governing aircraft safety and design. The standards are uniform across all categories of aircraft, and safety depends on adhering to these regulations without exception.