When it comes to maintaining aircraft safety and compliance, Airworthiness Directives (ADs) are non-negotiable, but that doesn’t mean they’re always fully understood. Despite the critical role they play in aviation maintenance, certain ADs repeatedly slip through the cracks—missed in inspections, misinterpreted in logbooks, or omitted entirely due to oversight or confusion. For A&Ps and IAs juggling a maze of documentation, time pressures, evolving regulations, and arguments with owners over airworthiness items it's easy for ADs to get sidetracked or worse, missed entirely.
In an attempt to highlight Airworthiness Directives that are frequently overlooked or misunderstood, we asked IAs and shop owners around the country for their list of “usual suspects” that were on their list. Here is our summary of that effort, with details below. (Note: please contact us here if we missed any!)
This AD requires a detailed disassembly and inspection of the ignition switch every 2,000 hours including proper lubrication with Luberex, a special grease. The AD also requires that an arc-suppression diode be installed at the starter solenoid (relay) if one is not already installed.
Not all ACS switches apply: ACS ignition switches that do not have a "start" position (models A-510-1 andA-510-5) or were manufactured on or after February 20, 1989, and have not accumulated 2,000 flight hours, need not be lubricated (these switches are identifiable by red paint in the screwheads on the back of the switch). However, manufacturer lubricated switches that have a"start" position, but do not have a starter solenoid diode, must be inspected.
Some mechanics have inadvertently signed off the wrong AD for the brand of switch (see 76-07-12, which requires a functional check every 100 hours). Because they are about 50% of the cost of the Bendix switches, they often end up in non-Bendix airplanes too.
Some mechanics assume that ACS switches manufactured after 1993 are not subject to AD 93-05-06, but that’s not what the AD says (!)
Finally, a "key test" should be performed to ensure the key cannot escape the mechanism in any position other than OFF. Teeth have been known to wear down over time and in some cases the key can slide out before the switch is in the OFF position.
This AD was issued after cases of magnetos not grounding properly, leading to “hot” mags and unintended engine start (or prop kick). It requires a functional test of the ignition switch every 100 hours for certain s/n’s.
The test can be performed by the Pilot, which involves rotating the switch (during run-up) through the "OFF" detent to the extreme limit of its travel in the "OFF" direction and checking to see if the engine continues to run. If it does, then you have a faulty switch.
Both this and the ACS/Gerdes AD (93-05-06) don't involve the "key test" which can be performed by ensuring the key can't come out of the mechanism when NOT in the OFF position. Remember - these keys were probably copied at Home Depot and the teeth aren't made of titanium: they are going to wear down like anything else. Remember to use the pilot's copy of the key (vs. a spare key at the mechanic shop).
This (recurring) AD was issued to prevent failure of the fuel injector fuel lines and clamps for certain Lycoming engines (over 37,000). Some engine models are omitted from the AD—not because the AD doesn’t apply—but rather because these engine models have the inspection listed in the airworthiness limitation section (ALS) of their maintenance manuals.
The service docs specifically calls out plastic ties and non-padded metal clamps (non-padded metal clamps require fuel line sleeves). Clamps should be secure and fuel lines should not be touching the engine or airframe baffle, requiring at least 3/16” clearance.
Even so, mechanics continue to see non-compliant metal clamps and loose clamps, perhaps that way for many years. Fuel lines must be inspected for dents, nicks, kinks, cracks, brittleness, chafing, or stains that might indicate a (potential) leak. The inspection is recurring every 110 hours TIS.
This AD has generated a lot of controversy given multiple types of impellers Lycoming used over the years (aluminum, iron, steel), PMA part overlap, engine variants, one vs. two-piece pump replacements, and service bulletin overlaps.
These impellers—small gear-like blades within the oil pump—were historically made from sintered iron and later from aluminum. The original sintered iron versions were prone to failure, prompting the original AD 81-18-04, which replaced them with aluminum impellers (LW-13775). Unfortunately, the aluminum impellers began failing too, leading to AD 96-09-10, which now requires the removal of both the sintered iron and certain aluminum impellers (unless they had already been replaced per previous ADs with the more robust steel gear and shaft).
Compliance with the AD depends on which type of impeller is installed. Note that while the AD doesn’t cover ALL aluminum impellers, Lycoming’s Mandatory SB 524 recommends the replacement of ALL aluminum impellers, regardless of vintage. In addition, SB 240 calls for replacement of oil pump bodies and gears (specifically the two-piece pump designs) at O/H.
This AD was issued to prevent engine failures stemming from prop-strike-induced damage to the engine, specifically the crankshaft gear retaining bolt. While inspection of the crankshaft gear retaining bolt is relevant, the reality is that prop strikes can afflict damage beyond the bolt.
There continues to be pushback on what should be defined as a “minor” prop strike. The AD defines it as, “Any incident during engine operation in which the propeller impacts a solid object that causes a drop in revolutions per minute (RPM) and also requires structural repair of the propeller (incidents requiring only paint touch-up are not included). This is not restricted to propeller strikes against the ground.” The AD specifically calls out situations where RPM is impacted but damage is not normally incurred, i.e., water, tall grass, or “a similar yielding medium”…
The reality is that prop strikes (of any kind) can put a lot of stress on the engine. While the AD only goes so far as to recommend “replacing a new bolt and lockplate” there may be other things amiss (for example, we’ve heard up to instances of cracked crankcases after sucking up a chock). As such, it is important to take a more holistic approach to minor prop strikes and enter the inspection with an open mind.
Every Cessna 172 pilot remembers two key moments: the first time they flew solo, and the first time they flew backwards in their seat (and that second one hopefully not on rotation)!
This AD was issued to prevent seat rail slippage and/or seat roller housing departing from the seat rail. Given the age of many of the Cessna aircraft out in the wild, this AD should be taken seriously. It is not unusual to read crash reports of post-take off stalls with seats found in the wreckage in “the full aft position”.
The inspection allows for no less than 0.42” diameter for the holes and no less than 0.02” of the locking pin below the holes. Rails, rollers, roller housing, springs, bushings, axles, tangs, and washers must be inspected every 100 hours TIS or every 12 months for wear, cracks, or deformations and replaced as necessary. A “No-Go” wear gauge is handy for this inspection, given the tolerances.
On second hand, owners can always have the seat stop installed for additional peace of mind (see Cessna SB07-5 Revision 6 or other PMA seat stops).
Complex compliance calculations and assumptions have caused this AD to be overlooked. After a series of fatigue-induced cracks were found in several PA-28 accidents, the FAA issued 20-26-16. Unlike simpler ADs, this one doesn’t specify a calendar or simple hour interval for all aircraft; instead, owners must dig through logbooks to count how many 100-hour inspections have been done in the plane’s life and apply a formula (which can be confusing).
This AD is about to undergo a break into two new directives for the eddy test and recurring inspection including spar cap bolt hole anomalies (see FAA-2024-2143 and FAA-2024-2142, respectively).
Given the (ever) increasing age of the fleet, cracks are more likely to develop with time, causing Piper and the FAA to conclude an eventual spar replacement and recurring inspection will be the only way to effectively reduce risk.
Nearly 5 years later, we’ve learned that a variety of anomalies in the bolt holes (corrosion pitting, scratches, gouges, or threading marks from improper loading are specifically listed). “While these may not present as fatigue cracks at the time of inspection, anomalies in the hole create a stress concentration where cracks can begin to grow,” the FAA states.
Because compliance essentially involves a visual check and sticker, some owners/pilots assume it’s simply cosmetic and may not realize it’s legally required. Luckily, this check can be performed by the pilot (note: this was added only after backlash given that you only needed the ability to tell left from right and up from down).
If improper (reversed clock positions) installation of the L/R fuel selector placards is found, you can fabricate and install temporary L/R fuel selector placards (as per SB 1309A) and then install a permanent placard within the next 100 hours TIS.
The AD requires repetitive detailed inspections of the entire stabilator control system and involves labor-intensive work in the tail that can be easily overlooked if not clearly documented. Compliance is every 7 calendar years or 2,000 hours TIS (whichever comes first).
At the time, it was argued that inspection of the control systems and pulleys are already part of the annual inspection; however, the FAA was quick to show multiple SDRs for cracks, corrosion, failure of the turnbuckle, control cable fraying, or cable swage end breaks for certain Piper models.
Some owners mistakenly believed it only applied to certain serial-number ranges or T-tail Pipers (in fact it also includes straight-tail Cherokees) and thus assumed their plane was exempt.
Because this AD says to follow the Piper SB 1245A, this SB is mandatory. Special emphasis is placed on disassembly of the turnbuckle bodies (again, mandatory) and cleaning using methyl ethyl ketone or acetone prior to inspection.
These ADs affect both the Cessna and F&M/Stratus (now Tempest) oil filter adaptors. An improperly maintained or installed oil filter adapter may lead to failure of the fiber gasket, which may result in oil loss or oil starvation.
AD 96-12-22 was issued to address an unsafe condition caused by adapter-to-oil pump threads fragmenting, resulting in loose or separated Cessna oil filter adapters. The AD requires inspecting the Engine Oil Filter Adapter assemblies (or torque putty, if installed) for oil leakage and proper installation of the adapter retainingnut and fretting of associated threads. You can get a special wrench to allow you to reach the adapter nut.
AD 23-17-04 was issued after the NTSB issued a report of multiple accidents stemming from oil starvation due to faulty or loose oil filter adapter gaskets and assemblies. The AD requires compliance withStratus SB001 Rev C, which highlights the improper usage of fiber gaskets (now discontinued) or re-using copper gaskets, which can lead to oil leaks. As ofthe effective date of this AD, fiber gaskets are no longer allowed onF&M/Stratus oil filter adapters.
AD 81-15-03 applies to Brackett engine inlet air filters with aluminum mesh and requires an inspection and/or replacement with a steel mesh. These aluminum mesh screens have a large welded-in diamond shape and were manufactured pre-1978. Installation of the gasket retainer strip only applies to certain models of airplane.
AD 96-09-06 applies to certain Brackett air filters with a neoprene gasket. These filters were getting particles sucked into the carburetor, resulting in partial or complete loss of engine power. Gaskets need to be inspected and replaced with new gaskets (new part #) within 500 hours TIS.
Finally, AD 02-26-03 affects Brackett filters with a single screen air filter assembly. Aircraft require an additional (front) screen to avoid (potential) failure of the air filter.
Many owners of affected Cessnas were caught off guard by these ADs, and some smaller shops were not prepared or qualified to do eddy-current tests, leading to delays. The AOPA also fought this AD, citing a “lack of evidence” and questioning the maintenance of the accidents that led to the NPRM/AD. The FAA responded that of the 211 inspection reports from 177-series airplanes, 120 aircraft had reports of corrosion (nearly 60%), with “at least 14 spars removed from service.”
Compliance time for the new AD 2023-02-17 is 12 months or 200 flight hours, whichever comes first. “We frequently see the N and R model aircraft that have only complied with the visual inspection and often the eddy current, but failed to comply with the final priming and application of corrosion inhibiting compound. To get credit for the AD, all of the SB steps called out in the AD must be completed.” Note: this includes sending a copy of the corrosion report to the FAA or Textron.
In 2015, Ameri-King’s ELTs were found to have multiple quality control problems – units were failing self-tests, not transmitting properly, or otherwise non-compliant with technical standards. The FAA took the unusual step of revoking the manufacturer’s TSO authorization and issued this AD to identify and eventually remove faulty ELTs from service.
This AD can be easy to slip through the cracks because the AD allows continued use of the ELT if it passes yearly tests which has led some owners to defer actually replacing the unit.
Are we missing any? Of course we are! Please contact us here.
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