Expert: Marc Ebelini - 5/19/2008

Question
I own a Cessna 150 and have some questions about how to proceed. My ELT Battery needs to be replaced, can I do this? Who is authorized to test an ELT? The transponder is up for bi-annual, if I can change my own ELT battery I can have them both tested at at the same time? The plane's annual is also due do I take care of the above first so the mechanic has it completed prior to his inspection?

Answer
You did not mention the type of ELT but I'll give my own opinion as to what I did when in business. Should have a qualified person open the unit to replace the battery and inspect the transmitter to make sure that there has been no oxidation or corrosion of the units components. Have no idea if you have an old unit that allowed battery fumes to leak into the transmitter section. Secondly, have the unit tested with a dummy load to verify the power and frequency and modulation. On air tests are allowed the first fives minutes after the hour and limited to three sweeps if I recall. If there is a FAA control tower or other station within receiving distant they should be notified. Because the antenna is disconnected to perform the detailed test I did the on air test with a field strength meter to assure that the antenna was radiating properly. The detailed tests and inspection are my methods that exceeded the legal requirements in some cases. Log book entries are required by licensed mechanics. Because like any other part of your aircraft once airborne it's too late. The date on the battery is important, but also is the condition. Never assume a new battery is good. FYI the field strength measurements assure that your antenna is good. Never assume because it's an antenna that it will radiate properly. Have replaced many defective antennas after a field strength test. The test could also reveal a bad RF cable.
Hope this satisfies your question.