Like hundreds of others, as a Private Pilot, I received the recent "Aviation Safety Letter" (ASL 2/2008) including the NSS ELT pamphlets. Having done a number of TSO certifications of ELTs as a Senior Engineer in Transport Canada, I am concerned at the continuing errors regarding ELTs in the aviation media and misleading statements, many through omissions, in much of the "official" information.
The pamphlet states that there are 2 types of ELTs: 121.5/243 MHz, (correct) and 406 MHz (wrong). This "406" label is misnomer and fuels a popular misconception that it has 406 MHz only, virtually all the "406" ELTs currently have 3 frequencies; it has 121.5/243/406 MHz. TSO C91a with the MOPS in RTCA / DO 183 gives the specifications for a 121.5/243 only ELT; for the "406" ELT, it must also meet TSO C126 and RTCA/DO 204. Thus, currently, all TSO-C126 (406) ELTs must meet both specs; while "labelled" as "406", they all must include 121.5 for homing as "406 does not lend itself to homing." The 121.5/243 signal is continuous, while the 406 is a single burst every 58 seconds. I have not heard of any "406 ELT" (unlike PLBs & RPIRBs that do not meet TSOC126) that does not also have 121.5, and to meet C126, it must have 121.5 and should also have 243, although Artex now has a two frequency unit, 121.5 and 406.
As outlined in paragraph 1.1 and 1.2, of DO-204, the 406 function is an "...optional adjuct..to 121.5/243.." and that any 406 standalone transmitter (ie PLB & EIRBs) is outside the scope... of DO-204" However, a revision to the RCTA spec, DO204A was just released in December and it incorporates the 121.5 specification as well as the 406 spec; the FAA are currently working on a revision to TSO-C126 to include 121.5 and 406 (without 243.0) as a "standalone" TSO not requiring TSO-91a (which does include 243); I have no timeline on this possible change.
Furthermore, a 406 ELT will not decrease the number of false alerts; however, it will make it easier to track the signal. It is a single three frequency unit in the same case, activated by the same G switch and radiating from a single antenna. The TSO environmental testing for shock, impact, crush, vibration, temperature and mounting is identical, word for word in both DO183 and DO 204.Prior to SARSAT, there were other methods of "alerting"; depending on the type of operation, there are many ways "of mitigating the risk" without SARSAT.
ed. Jim's experience as a Certification Engineer brings a perspective to this issue that confirms what COPA has been emphasizing regarding the limitations of devices that must survive an accident in order to do their job. Mandating 406 ELTs for our sector of aviation will not appreciably change the prospects of being found. There are several affordable alternatives but they are not permitted in place of an ELT. Readers are urged to visit our website (www.copanational.org) for more information and then help us fight this misguided regulation by contacting their Member of Parliament.