During a recent trip south, we took our 406 ACK Emergency Locator Transmitter for recertification and installation of a new battery. To our surprise, on the return trip, a diligent security official decided to verify that the unit didn’t exceed the maximum allowable watt-hour (Wh) rating for a battery in carry-on baggage.
According to CATSA guidelines for transport of lithium batteries, any lithium battery over 160 Wh cannot be carried on board an aircraft. The Wh rating of a battery is calculated as its voltage multiplied by its amp-hour (Ah) rating. Since neither rating was specified on our unit, the security official had to "perform a calculation". After examining the label on our unit and doing some math on scrap paper, he determined its Wh rating to be 170 Wh, and announced that we must leave security and somehow place the ELT in our checked baggage.
Motivated by extreme reluctance to be separated from our ELT and its expensive new battery, we questioned the "calculation". It turned out that the security official had scanned the label for any number that might relate to amperage, finding only TSO C-142a, which he then creatively multiplied by the voltage of the unit. After explaining that a TSO number is not an electrical rating, we were able to quickly Google the installation/operating manual for our ELT and convince the official that its Ah rating was only 7.75 Ah. The correct Wh calculation therefore yielded 93 Wh, so the official graciously apologized for the confusion and allowed us to carry the ELT on board.
The moral of this story is to know your ELT. Better yet, travel armed with its specification sheet which clearly indicates the size of its battery.