ELT Inspections Under 14 CFR 91.207: The Annual Check and the Battery Clock Every Flight School Trainer Has to Track Separately

A 172 came back from an annual on a Friday with a fresh logbook entry and a clean squawk sheet. The chief instructor released it for a Saturday solo. Nine days later a different CFI pulled the airframe log to confirm the next 100-hour due time, scrolled past the annual signoff, and noticed the ELT battery-replacement date on the unit was already eleven months old, with the battery itself rated for a 12-month service life. The annual had inspected the ELT. The battery clock had not reset. The airplane had flown sixteen hours of instruction in a state the FAA would call unairworthy, and the chief instructor spent the afternoon understanding why the dispatch screen showed a current ELT inspection and said nothing about the battery.

14 CFR 91.207 is the rule that makes the emergency locator transmitter a dispatch item with two clocks instead of one. The 12-month inspection is one clock. The battery-replacement requirement is a separate clock, on a separate cycle, against a separate manufacturer specification, and the two only line up in a school whose tracking system was built to keep them apart.

What 91.207 Actually Requires

14 CFR 91.207 says that no person may operate a U.S.-registered civil airplane unless an approved automatic-type ELT is attached, the ELT is in operable condition, and the airplane meets the rule's limited exceptions. The exceptions are narrow enough that a flight school trainer almost never qualifies for one. The rule then layers two recurring obligations on top of the installation.

The first is the 12-month inspection. The ELT and the installation have to be inspected within 12 calendar months after the last inspection for proper installation, battery corrosion, operation of the controls and crash sensor, and the presence of a sufficient signal radiated from its antenna. That inspection has to be recorded in the maintenance records under Part 91.

The second is the battery clock. The rule requires that the battery used in the ELT be replaced, or recharged if rechargeable, when the transmitter has been in use for more than one cumulative hour, or when 50 percent of the battery's useful life, or for rechargeable batteries 50 percent of its useful life of charge, has expired. The expiration date for replacing or recharging the battery has to be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record.

The 12-month inspection and the battery replacement are not the same event. A shop can perform the inspection without resetting the battery date. A new battery can be installed without performing the inspection. Either entry by itself is partial compliance, and the airplane is not legal until both are current.

The 121.5 to 406 MHz Shift the Rule Lives Inside

The rule points at an "approved" automatic ELT, and an installed 121.5 MHz unit still satisfies 91.207 on a U.S.-registered Part 91 airplane. The operational reality is different. The international satellite system stopped processing 121.5 MHz alerts in 2009, and the airplane whose only ELT is a 121.5 unit is broadcasting on a frequency that no longer reaches the satellite network search-and-rescue uses to find an airframe. The FAA's Advisory Circular 91-44 lays out the operational case for 406 in language a school can hand to an owner during a leaseback conversation.

A 406 ELT also brings a self-test, a registration requirement with NOAA, and a 24-bit hex code that ties the transmitter to the airframe. A school that replaced a 121.5 with a 406 and never registered the new unit has installed a transmitter that will not be tied to the aircraft in a real activation. Registration is free, runs through the NOAA beacon registration portal, and renews every two years. The school's annual airworthiness sweep should re-verify the registration is current the same way it verifies an ELT inspection entry is in the log.

Why the Two Clocks Drift Apart

A 12-month inspection done on 14 March 2025 is good through 31 March 2026. A battery whose marked expiration date is 1 August 2026 expires on 1 August 2026. The inspection clock is calendar-month bounded, the battery clock runs against the manufacturer's marked date, and there is no version of the rule that says the inspection resets the battery clock or vice versa. The reason schools get caught is that the annual sweeps the ELT inspection forward 12 months and leaves the battery date alone. The dispatch screen shows the inspection as current and says nothing about the battery.

The cumulative-use trigger is the other half of the battery clock. A test activation that exceeds one cumulative hour, or an inadvertent activation after a hard landing the crew did not notice on the rollout, resets the replace-on-use threshold regardless of the marked date. A school whose test policy is the standard three sweeps on the hour will not approach the cumulative hour for years. A trainer that took a firm landing, set off the ELT for an hour before the next preflight noticed it, is closer to the trigger than the binder records.

Where the ELT Sits Inside 91.213(d)

An ELT that is inoperative, an inspection that is overdue, or a battery past its marked date is not a 91.213(d) deferral candidate in the usual sense. 91.207 names the ELT directly as required equipment, and a school cannot placard it inoperative the way it might placard a static-system drain valve under a properly built MEL.

The narrow path that does exist is 91.207(f)(4), which allows operation without the ELT installed for up to 90 days when the unit has been removed for inspection, repair, modification, or replacement, provided the records show the removal date and the airplane is placarded "ELT not installed" in clear view of the pilot. That paragraph is for an ELT that is out of the airplane, not for one that is in the airplane and lapsed. A school that misreads the 90-day window as a grace period on an expired battery has invented a deferral the rule does not give.

Mechanic Signoff and the Maintenance Record

The 12-month inspection has to be performed and signed by a properly rated mechanic, and the entry has to name the four 91.207(d) items. A school that lets the annual signoff stand in for a separate ELT inspection entry is clean only when the annual entry itself enumerates them. Most thorough A&P entries will. A few will not, and the airworthiness records the next FSDO inspector reads cannot leave the question to interpretation.

The battery date is a different entry. It has to be marked on the outside of the transmitter and recorded in the aircraft maintenance record. The discipline is the same as any other recurring airworthiness item: a single source of truth for the date, a visible field at dispatch, and a re-read after every shop visit to confirm the entry transferred from the work order to the airframe log.

Tracking Both Clocks at Dispatch

A school that holds the ELT inspection due date and the ELT battery expiration date as two structured fields on each aircraft, alongside the annual, the 100-hour, the 91.171 VOR check, and the 91.411 and 91.413 bench checks, is a school whose dispatcher sees the next-due date the same way they see the engine TBO. Soft flags fire 30 days out. Hard blocks fire on the day either clock lapses.

A modern flight school management platform can hold those fields as first-class aircraft attributes and read them into the release decision automatically. The school that tracks both clocks in a shared spreadsheet and trusts the chief instructor to remember which trainer is next is the school whose ELT eventually slips past someone.

Pair the Battery Change With Scheduled Maintenance

The cleanest pattern is to plan the battery change inside a maintenance event whose downtime the school has already absorbed. A school that lines up the next battery change with the next annual gives itself a 12-month operating window where the two clocks stay aligned and the dispatch screen has one decision to make instead of two. The trainer whose battery date and inspection date drift across three cycles is the trainer whose next slip will be on the clock nobody was watching, and the chief instructor is back to writing a process on a Saturday after a flight that should have stayed on the ramp.