We all know, or think we know, the possible pitfalls of non­compliance with a regulation. The discussion today is focused on Airworthiness Directive (AD) compliance. Worst case for non­compliance is that some terrible tragedy isn’t averted. The best case is that the missed AD is discovered and complied with before anything bad happens. Somewhere between those two is the paperwork nightmare that may happen if the FAA finds out. On occasion we find where an AD is being repeatedly complied with even when it doesn’t apply. Usually, there’s no real harm except to your wallet.

When an AD is determined to be a recurring event, there may be a terminating action. If so, it’s common to find an entry in the maintenance records describing the action taken and a statement similar to “No Further Action Required” or NFAR. This is a powerful statement with regard to FAA mandated airworthiness directives and often underused. There are a few specific cases in point.

Ignition Switches

We find this to be the most commonly confused component on the plane. The three most common ignition switch manufacturers for the Cessna single engine line are Bendix, ACS and Gerdes. With those there are two ADs that may apply. Our experience is that mechanics assume the Bendix switch is installed, but the ACS and Gerdes are just as likely to be installed. Considering the legacy planes are all in excess of 30 years old, there’s been plenty of time for ignition switches to be replaced a couple of times.

                    93­05­06 ACS and Gerdes: Disassemble, inspect for wear and corrosion, lubricate and reassemble. Repeat every 2000 hours. Also add a diode across the starter solenoid.

                    76­07­12 Bendix; Perform operational check to verify the mags stay off when the switch is rotated far left. Repeat every 100 hours. Only applies to certain part numbers and those without a date code or white adjacent to the Bendix logo.

There’s no harm in doing an operational check every 100 hours on an ACS or Gerdes switch. Also, no particular damage with inspecting and lubricating a Bendix switch every 2000 hours. There could be serious harm if one doesn’t also perform the proper AD on the switch to which it applies. To be sure that happens, one must first take the time to actually look at the installed switch to confirm which one it is.

172R & 172S Fuel Servo

The restart 172 series fuel servo has a possible problem with over rich mixture at low RPM. This causes concern with the engine’s ability to reliably restart in flight. This AD is somewhat unique in that it applies to an accessory but isn’t listed in the AD accessory category. It’s mounted to an engine as part of the engine FAA type certificate, but a search for ADs applicable to this engine won’t return any hits on the servo. This AD only shows as a Cessna 172R or 172S application.

                      2001­06­17 Cessna:  A specific operational test must be performed to determine the idle speed and mixture settings. If adjustments must be made, the test is to be                                                        repeated within 25 flight hours. If the adjustment must be repeated more than twice over a 12 month period, one must contact the FAA

This AD requires some close reading as it can seem to imply the operational check is a continually recurring requirement. It isn’t uncommon to find compliance with this AD documented at every annual for many years. The AD is only intended to be repeated to confirm the stability of the adjustment. Once that stability is established the AD can/should be signed of as “No Further Action Required”.

Flap transmission

This is one of my favorite oldies, and I still see the recurring portions of it being documented as complied with. When reading through all the paragraphs and steps, one should pay close attention to the repetitive compliance times: hourly and calendar. Consider the time frame from the effective date of the issuance of the AD; then note the terminating action time.

                      72­03­03 R3 Cessna: A good inspection of the flap actuator jackscrew every 100 hours and complete removal for cleaning and relubrication if any problems are noted cleaning. If the plane’s total time is above 500 hours, go directly to the jackscrew removal and cleaning step. Regardless of flight time, remove the jackscrew for cleaning and lubrication every 12 calendar months. These requirements are all spelled out in the AD paragraphs A, B and C. Paragraph D says to modify the plane before January 1973 (the AD only became effective 11 months prior). Paragraph E then says once paragraph D is complied with that paragraphs A, B & C are no longer applicable.

Anyone experienced in maintaining these Cessnas knows how important it is to keep the flap jackscrew clean and well lubricated. Continued inspection, cleaning and lubricating of the jackscrew isn’t a bad thing. Documenting it as continued compliance with the AD just exposes a lack of understanding that terminating action for all aspects of the AD was required no later than January 1, 1973. It would be great to find a log entry stating “No Further Action Required” from early 1973.

Air Filters

The key word in the Applicability statement of this AD is “paper”. It does not apply to any filters constructed using any other medium.

                      84-26-02: This AD applies to all paper induction air filters used in small airplanes and requires replacement by 500 hours in service regardless of condition.

The concept for this article was a conversation I had with fellow CPA member Ron Gatewood at Airventure 2015. He asked me about the applicability of AD84-­26-­02 for paper induction air filters on the currently produced filters. Of concern was whether this very old AD applied to current production air filters that may not be made using a paper medium. He had contacted Cessna and the filter manufacturer, but no definitive answer was given. He tried the FAA who didn’t want to talk about it.

I hadn’t given the old AD much thought as most induction air filters get replaced before the 500 hour stated limit due to debris (dirt, bugs and such) restricting air flow. I often see this AD listed in aircraft records and signed off at every annual even when the old paper filter has long ago been replaced by a foam style Brackett filter. Not that air filters shouldn’t be replaced at or before 500 hours time in service, but it does seem important to know if it’s an FAA requirement. To that end, I promised Ron I’d find out about the paper air filter and report back.

As it turns out, it only took one phone call to settle the question. The most common paper looking filter is produced by Donaldson, so I started there. Scott Peterson at Donaldson was very helpful and explained that his company had not produced air filters with paper medium since 2008. All production since that time use a fiberglass base medium to which the AD obviously would not apply. He went on to clarify that a quick way to distinguish an old paper filter from the newer fiberglass is color. The fiberglass is white, and paper is about the same color as a paper grocery bag.

To my knowledge the main producers of aircraft induction air filters are Donaldson, K&N and Bracket. None of these use a paper medium, so unless you see a filter that is brown, the AD doesn’t apply. If you do happen to find an air filter that’s brown or has turned brown, paper or not, it’s telling you it needs to be replaced.

The Note in the AD states “This AD does not alter current maintenance procedures which require inspection of paper induction air filters at 100 hours time-­in­-service and annual inspections and replacement as necessary based on filter condition. “ The FAA does not give any time limits on air filters. Instead, they require replacement only as necessary based on filter condition.


I’ve been told my writing gets a little “preachy” sometimes, and I suppose this time is no exception. The FAA says the responsibility for the aircraft’s airworthiness AND ensuring compliance with airworthiness directives lies squarely on the shoulders of the owner/operator. There may be no harm in doing all these extra checks, inspections, parts changes if you want them performed. It seems good to me that we show our attention to detail in our record keeping by not documenting actions as AD compliant when there’s “No Further Action Required”.

Copyright © Paul New 2016. All rights reserved.