Public Penance

Every now and then, a mechanic drops me a letter. Many of these letters make great safety suggestions and others rag on me about the FAA in general, or a particular ugly regulation, or both.


Before I get another letter, let me state that you can still repair, replace, and recharge batteries in the old TSO-C91 ELT. However, when the old ELT gives up its electronic ghost, you must replace the older designed ELT with one built to the new TSO-C91a standards. They cost more, but tell your customers a new ELT is a lot cheaper than a funeral.

About ELT installation - The 1994 rule states that the ELT must be physically attached to the aircraft. An ELT stuffed in a seat pouch does more harm than good. The same can be said for a poor installation. A few years ago a Beech Bonanza crash-landed, wheels up, in a farmer's field in southern Maryland . Despite minimal damage to the aircraft (the aircraft was flown from the field), the pilot was killed. The cause of the fatality was the pilot-installed ELT that had been mounted onto a fiberglass hat shelf in the back of the cabin. When the aircraft slid to a stop in soft earth, the ELT was ripped off the hat shelf by the sudden deceleration and struck the pilot in the back of the head; killing him instantly. Thus said, I recommend that all mechanics double check pilot-installed ELTs.

ELTs must be installed in a protected area of the aircraft where, in the event of a crash, damage to the transmitter is minimized. Also, the ELT must be located as far to the rear of the aircraft as practical. "As practical" on some aircraft might mean behind the rear passenger seat. This type of ELT installation must also allow for inspection and maintenance. If the ELT is installed so far back in the aircraft's tail that only very tiny people with belt buckles on their shoes can get back in there to check the ELT, it is not an "as practical" installation. So, each ELT installation becomes an exercise in common sense.

ELT inspection requirements: (TSO C91 and TSO C91a)

FAR section 91.207 requires that an ELT must be inspected every twelve months for proper installation, battery corrosion, operation of the controls and crash sensor, and for the presence of a sufficient signal radiated from its antenna. The presence of a sufficient signal was what I failed to elaborate on at the Gulf South seminar.

The inspection must be done in accordance with the ELT manufacturer's instructions. If none is available, the following instructions are acceptable:

1. Remove all interconnections to the ELT unit and ELT antenna. Visually inspect and confirm proper seating of all connector pins. Special attention should be given to coaxial center conductor pins that are prone to retracting into the connector housing. Also check for corrosion on the pins.

2. Remove the ELT from the mount and inspect the mounting hardware. All required mounting hardware should be installed and secured.

3. Open the ELT and inspect the battery and its compartment. No corrosion should be detectable. Verify that the ELT battery is an approved one and check its expiration date.

4. Activate the ELT using an applied force. The direction for mounting and force activation should be indicated on the ELT. Using a quick rap with the palm can activate a TSO-C91 ELT. Use a rapid forward (football throwing motion), coupled with a rapid reversing action for a TSO-C91a ELT. Check if the ELT is still working by verifying ELT activation with a wattmeter, or the aircraft's VHF radio tuned to 121.5 MHz, or by other means.

5. Re-install the ELT into its mount and make sure it is installed in the proper position for crash activation. Reconnect all cables, ensuring they have some slack, and are properly installed, protected, and supported for their run.

6. Activate the ELT using the "on" or "test" switch. A low-quality AM broadcast radio receiver should be used to determine if energy is being transmitted from the ELT antenna. When the radio is held about six inches from the ELT antenna, and is set on any AM station, the ELT aural tone signal should be heard over the radio's speaker. The aircraft's radio tuned to 121.5 MHz can also be used. To ensure that the signal is being broadcast over greater distances, you can position a second aircraft about 300 yards away and turn on its radio to monitor 121.5 MHz. Or, if you are at a controlled field, contact the tower and ask them to monitor the ELT signal.

Remember, please test ELT only within the first five minutes after the hour and limit the test to just three sweeps of the transmitter audio modulation.

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