In a move designed to accelerate the transition from 121.5 MHz to 406 MHz emergency locator transmitters (ELTs), the Federal Communications Commission last week issued a new rule prohibiting certification of the 121.5 MHz units. But the rule continues to permit the use of 121.5 MHz ELTs.

The rule follows a previous rulemaking in which the FCC had prohibited the sale, certification, and use of the 121.5 MHz ELTs. The agency, however, stayed that action after the FAA and the Aircraft Owners and Pilots Association appealed to the FCC to revisit the decision, citing concerns about the costs of equipping with the 406 units and the belief that 121.5 MHz still provided some benefit.

Over the past couple of decades, organizations administering the Cospas-Sarsat international rescue program have pushed for adoption of the more advanced 406 MHZ ELTs and by 2010 the Cospas-Sarsat system limited tracking of ELTs to 406 MHz. The FCC said this eroded the utility of 121.5 MHz. Saying it “continue[d] to believe that a phase-out of 121.5 MHz ELTs is in the public interest,” the FCC followed in 2013 with a future rulemaking proposal.

The agency followed with the rule published in the December 12 Federal Register that immediately prohibits certification of new 121.5 MHz units and prohibits the manufacture and sale of them after a six-month transition period.

“The record demonstrates that 121.5 MHz ELTs were clearly inferior to 406 MHz ELTs due to interference and other concerns even prior to the termination of satellite monitoring of 121.5 MHz and that the advantages of 406 MHz ELTs have increased since then,” the agency said.

Despite arguments otherwise, “the great weight of the record evidence indicates that [the 121.5 MHZ ELT] benefits are marginal at best,” the agency said, and added “Although it appears that most GA aircraft owners and pilots are aware that satellite monitoring of 121.5 MHz ELTs has ceased, some users may place unwarranted reliance on the protective value of 121.5 MHz ELTs.”

Supply of the 406 MHz units is now sufficient to meet demand, the agency further said, and costs have dipped below $600 per unit.

However, the agency is declining to mandate the use of 406, believing that the transition to the higher performing units will occur naturally over time or that other technologies, such as ADS-B, may overtake the need for such a mandate.  The FCC further questioned whether such a mandate might get entangled in legal challenges.