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.

I promise you that I read and answer every mechanic's letter sent to me, because these kinds of letters number so few. I suspect the reason I have a near empty in-box is how mentally uncomfortable a mechanic feels about "waking up" a bureaucrat in Washington . Many mechanics have this unnatural fear that their name will go on a black list – entered into a big computer buried deep somewhere in the bowels of FAA's Washington headquarters. Once a name is entered, it remains forever listed with others who have fallen from bureaucratic grace, in a encrypted file titled: People we get next!

So, to avoid unwanted grief, most mechanics are content to put up with the FAR fleas, just to let bureaucratic sleeping dogs lie. But there are always exceptions to this rule. One such exception is a mechanic by the name of August Blake, an IA from Louisiana . About once or twice a year, August writes me a letter, and despite my earlier statement that I read every letter from a mechanic, I must admit that I am a bit reluctant to pick up and read August's letters. Why? Because 99 percent of the time he chews me out, and 99 percent of the time, he is right.

Last week, August sent me another letter. Like the true southern gentleman he is, August first complimented me on my maintenance presentation about ELT inspections at the Gulf South seminar. But, August then pointed out that I did not properly cover all of the ELT inspection requirements in part 91, section 91.209, Emergency Locator Transmitters. Okay, August, you are right – again – so, in public penance for my mistake, what follows is a complete description of the ELT rule and inspection requirements.


Emergency Locator Transmitters (ELTs) became part of our aviation environment with the signing of the 1970 Occupational Safety and Health Act. Not many people are aware of the fact that the original requirement for ELT installations was a congressionally driven law, not an FAA inspired regulation.

As required by the new act, the FAA followed up with an implementation regulation that required ELTs to be installed in a majority of the general aviation fleet by June 30, 1974 . Some early exceptions were that ELTs were not required for aircraft on local training flights, ag aircraft, R&D aircraft, single-seat aircraft, rotorcraft, and turbo jets. Later ELT exemptions pertained to aircraft showing compliance with the regulations, crew training, exhibition air racing, and market surveys. The early ELTs manufactured under TSO C91 were less than 100 percent successful. Models with lithium/sulfur-dioxide batteries vented corrosive, and sometimes explosive gases. Other ELTs had hair-trigger "g" (crash sensor) switches that fired off the ELT if an overweight gnat landed on the propeller tip of an aircraft tied to the ramp. Improper installation of the ELT, hard landings, antenna/wiring faults, or just plain internal failure of the transmitter's innards, caused other ELT false alarms. Despite the millions of dollars wasted annually on false alarms, the early ELTs did save a number of lives. But, the continuing failure rate of an aviation product caught the attention of the National Transportation Safety Board (NTSB), who in 1988, issued NTSB Safety Recommendation A-87-104 which suggested existing ELTs be replaced with those that complied with TSO-C921a by 1989. In October 1990, (NASA) National Aeronautics and Space Administration and the FAA completed a report entitled Current Emergency Locator Transmitter Deficiencies and Potential Improvements Utilizing TSO-C91a ELT. This report was the driving force for the June 21, 1994 FAA rule change to part 91, section 91.207, which mandated all new ELT installations to meet TSO-C92a. The new rule did three things: 1. terminated the manufacture of ELTs under the old TSO-C91; 2. required that as of June 21, 1995, all new installations and replacement ELTs must meet TSO-C91a; 3. made mandatory inspection and recording requirements specific to ELT installation.

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.

Other important things

You are required to change the battery if it has been used for more than 1 cumulative hour, or when 50 percent of the battery's life has expired. For chargeable batteries, change when 50 percent of its charge's useful life has expired. If good maintenance records are kept on each test of the ELT, a mechanic should have a good idea of the state of the ELT's battery life. But, short of an actual bench test, even with the right equipment, it may be very difficult to determine if an ELT battery's life is less than 50 percent. If in doubt, change the battery - it's just too risky not to.

Remember, the job is not done until the paperwork is finished. Don't forget that you must record the date of the ELT inspection, and the date of the ELT battery's last replacement or charge on the outside of the transmitter as well as in the aircraft's maintenance record. Strangely, the FAR 91, section 91.207 requiring an ELT to be installed, inspected, and maintained, allows for the aircraft to be operated up to 90 days without an ELT, if the following procedures are adhered to. The aircraft maintenance records must contain an entry that includes: the date of the initial removal of the ELTs well as its make, model, serial number, and the reason why the ELT was removed (e.g. maintenance). Also, a placard must be made and located in view of the pilot that says "ELT removed."

Mechanics should be wary on performing an annual inspection in which the aircraft records indicate that the pilot removed the ELT, reinstalled it, and removed it again on a continuous rotating basis every 90 days. While not exactly illegal, it is stupid, so diplomatically explain why an ELT is a very important part of a safe flight.

Well August, my public penance is over. Now if you'll excuse me, I have an entry to make on the computer in the basement.