I was recently performing incoming operational checks on a Cirrus that arrived for its annual inspection, and I noticed an interesting semi-non-maintenance topic, VOR checks. A VOR check is not part of the minimum scope and detail of an annual inspection according to the FAA in Title 14 CFR 43 Appendix D. What the FAA does require is an inspection of the physical installation, mounting, wiring, bonding, antenna installation and operation. There’s no specific requirement to make sure any of the avionics function properly and certainly no call to calibrate anything. The Cirrus Maintenance Manual Chapter 5 for Time Limits and Maintenance Checks also has no requirement or even a suggestion that any operational checks of the avionics systems be performed during an Annual or 100 hour inspection. That means it’s up to you, the pilot/owner/operator to ensure that the avionics are always in good working order.
The 30 day VOR check requirement is found in FAA CFR 91, where all the owner/operator responsibilities for aircraft systems are listed that must either be performed by the owner/operator or that the owner/operator must ensure are performed. On this day I just happened to be near our airport’s VOR test point during this pre-maintenance taxi, so I thought I’d just give it a go. As it turns out, one of the airplane’s VORs tested several degrees out of the allowable range. I feel a moral obligation to report the impromptu finding, but there’s no FAA obligation for me to suggest the owner take any airworthiness action. I didn’t find any record showing history of these checks in the aircraft, but it’s very possible that the owner has some sort of notebook at home to track these checks.
To be clear, a working VOR is not an airworthiness requirement. A failed VOR system, or one that fails the required 30-day test, does not “ground” the airplane even if discovered by the inspector during an annual inspection. It only limits the airplane to flight that doesn’t require an operating VOR or as is limited in the POH. The inoperative system can be placarded as inoperative and disabled and remain that way indefinitely.
Since we’re talking about airworthiness requirements, there are several systems that are often assumed to be required for an airworthy annual sign off but are actually just flight limitations. Alternator #2 as well as Battery #2 may be inoperative for VFR flight (see the POH). Navigation lights are only required for night operations (see POH) and thus are only a flight limitation, not an airworthiness requirement. A quick read through the POH Section 2 Limitations reveals a very long and interesting list of things that can be inoperative. The 24-month IFR recertification required by CFR 91.411 and 91.413 is only required for IFR flight and flight into certain airspace. Even the ELT is not an airworthiness requirement, but it does have to be working if one wants to fly far enough away from home to actually get to another airport.
The list continues but the important note is that many things we assume to be required for airworthiness are simply flight restrictions. As an FAA certificated Airframe and Powerplant mechanic with Inspector Authorization, it is totally legitimate for me to sign off an annual inspection as airworthy with any number of nonrequired systems appropriately disabled and placarded as inoperative. Of course, what one can do isn’t always what one should do.
There are also the items that owner/operators assume are being thoroughly checked at annual for which there is no actual requirement in the annual/100 hour check lists. The VOR is the one that got me going down this rabbit hole, but there are others, like the fuel quantity indication system. During inspection we power up the aircraft and look to see if there is an indication for fuel level in the tanks. If the displayed amount seems reasonable, all is good. Of course, fuel level indications can read all sorts of wrong when in-flight, including Red X or CAS messages, but many of those won’t present in the calm of the maintenance hangar. That means it’s up to the owner/operator to report any difficulties with these systems for maintenance providers to know to have a deeper more purposeful investigation.
Circling back around to the owner/operator procedures for disabling equipment, Title 14 CFR 91.213 gives details for how and when an item/system/component may be inoperative for flight. Simply slapping an “inop” label isn’t it. The equipment must be disabled as well. Disabled may be just turning it off or pulling the circuit breaker. If that isn’t an option, the equipment must be removed from the aircraft. Removal also invites the question of whether a revised weight and balance must be generated. It all seemed so simple until we dig into the regulations to see what must be done.
Before one flies with inoperative equipment, one should be certain of all the consequences of that flight operation and plan accordingly. Of serious consideration is whether these disabled systems will increase the flight workload or cause too many work arounds. Those work arounds can pile up into serious problems when the flying gets complicated.
So, back to the VOR 30 day check. 91.171 says no IFR if it doesn’t pass. There are four possible methods for doing the test and different error allowances depending on which method is used. The last bit is a requirement for a signature attached to each check. With all our technology we really want to record this test on some sort of electronic device. I’m sure there’s a way to include a signature on a tablet, but I’m not that tech. I just jot it down on a handy note pad that hangs out in my plane. The record of the check only needs to be retained until the latest check is recorded. I can lose the pad and not worry about it.
Putting this all together, one should always remember that the owner/operator is ALWAYS the one responsible to ensure the aircraft is airworthy. What one thinks the annual inspection covers may not even be on the list. If you aren’t sure what’s on the list, just ask your inspector for a copy of the checklist they use. Anything not on the list is up to the owner/operator to monitor and report troubles to ensure all is taken care of. As always, it’s Owner in Command when we talk about maintenance.
©Paul New 2025
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