An Avionics Annual

Every year you have an annual inspection on your plane (or possibly a progressive inspection), but did you know that the FAA also highly recommends that your avionics also have an annual inspection? As the editors of Light Plane Maintenance recently explained, its spelled out in some detail in the latest AC 43.13-1B, but there is some bureaucratese to wade through.


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The FAA recommends an annual inspection for youravionics and we recommend it highly as well. Well give you the gist of it andthen some in the words that follow. Next month, well also give you somelow-buck alternatives for test equipment to perform more detailed avionicssystem checks. By the way, dont count on your IA doing these avionics checksduring your annual. His plate is quite full just doing all the FAA requiredmechanical and paperwork inspections without doing all the recommended avionicsthings as well. The reasons are clear: time and money. People want things donequickly and as cheaply as possible.

Adding in all the extras to give your avionics and instrument systems ahealth check would drive your annual expenses too high, without yourunderstanding of the importance and advantages of these checks. Nevertheless, anavionics inspection is really time and money well spent, particularly if you flyIFR, but even if not, why wait for an in-flight failure to discover problems?

These inspections can run the gamut in level of detail and difficulty, fromsimple visual inspections to using test equipment to check how well youravionics are performing. The majority of this inspection process doesntrequire an A&P rating, since most things are simple checks where nostructural disassembly is required-only the expenditure of time and attentionto detail.

The payoff is finding problems before they are in-flight failures-which weall know seem to happen at the worst possible times. Additionally, you can helpto make sure your equipment performs up to specification. A secondary payoff isincreased troubleshooting ability when things do go wrong en route. A thirdpayoff is being better able to describe the nature of a malfunction to avionicsshop personnel. Sounds like a win, win, win, at the expense primarily of alittle time.

What follows is a list of suggestions as outlined in FAR 43 Appendix D, plusour take and recommendations. One caveat is that if you find a situation thatrequires disassembly outside the guidelines of preventative maintenance outlinedin Part 43, Appendix D, you need the supervision of an A&P to stay100-percent legal.

Inspection Guidelines

Access under the panel varies from bad to worse in many airplanes, but ifyour body allows it, inspect all wiring bundles for proper security, and thatthey are not rubbing on any controls when you move them through their completelength of travel. There should be no signs of overheating or wire discoloration.

If you find lots of wayward unmarked wires not properly secured, it may betime for an avionics shop to have a look, as this is a sign that unqualifiedpeople were doing repairs with who-knows-what types of unapproved wires fromRadio Shack or surplus city.

Older airplanes should be particularly checked for deteriorating wires suchas cracks in the sheath that invite moisture and ultimate failure or even afire. Some shops recommend five-year change outs of wiring harnesses, which isnot going to happen. Most people simply will not spring for wholesalereplacement of a functioning system at this interval-and its certainly notrequired for Part 91 airplanes. In fact, time limited parts are rare in ourclass of airplanes; most parts are replaced on condition based on an IA or shopinspection.

That said, even the best wires (with the possible exception of Teflon) willdeteriorate over time, and cracked wires are downright dangerous, so you need todecide if this is a danger you want to risk. Its not only the failure that istroubling, but also the fire potential. Dont count on the IA finding thiscracked wire, unless you specifically ask him to check.

Dont confuse surface cracks with imminent failure. Factory original wireparticularly has two coats of covering, a slick plastic-like outer film, and aninner insulator. The outer film generally goes first, while the inner coveringis still intact. If you find this, consider it a flag to plan for replacementrelatively soon-at least those wires exhibiting such deterioration if thereare only a few.

Coax Cables

fuselage wiring

This wire also fails, but generally its a performance failure from age orcorrosion. If coax is improperly installed with tight bends rather than rightangle connectors, the inner conductor will migrate and change impedance fromideal to arbitrary. The result is poor avionics performance-particularly incomm radios. Junk connectors or bad installation of good connectors has asimilar result.

Coax sitting in the fuselage belly is particularly prone to problems sincethis is where most moisture will be found if any. Coax connectors like standardBNC types are not weatherproof without the help of an external covering, so beon guard for problems here. Coax should not be able to flop around in flight, asthis guarantees its early demise.

So if you find any loose coax in the fuselage, it needs to be properlysecured and run away from any power lines. In spite of an external shield, itwill succumb to interference if run too close to power carrying wires.

Some coax is nearly physically bulletproof, such as RG-142 BU, which has aTeflon outer jacket, heavy shield braid and an inner insulator of Teflon ratherthan polyethylene. Its also extremely expensive and very stiff to work with.You may find it in a DME or transponder installation, since it has significantlybetter performance at those frequencies. The connectors are still not immunefrom weather problems, however.

Mechanical Connections

Avionics gear is generally secured both at the front and back of the boxdepending on weight and length. If the rear ends of the radios are allowed towag in flight, as some amateur installations are, the radio may well snap thefront mounting screws or other mounting hardware. Make sure mounting racks arewell secured, and that there is no lose hardware. Even the newest avionicsshould be installed with some clearance between boxes for air circulation.

Also make sure avionics can breathe. If there are cooling ducts, make surethey are free and unobstructed. Something could come loose in flight and block acooling duct, or a wire could come loose to a cooling fan. Check this.


Antennas can take quite a beating. Some can be observed in flight vibratingto beat the band. Obviously the mounting and antenna itself is subject todeterioration both from the weather and the flight environment.

Check the security of your antenna mounts, and be sure there is nodeterioration of any seals. If water gets in there, it can deteriorate thequality of the ground point and reduce or lose antenna effectiveness. If theantenna is physically loose, you have a problem that needs immediate attention.

Antennas encapsulated in fiberglass or plastic housings also can suffer froma crack in the housing, which allows corrosion and deterioration of the activeantenna element. Check to be sure the outer antenna sheath is in good shape.Also, be sure that antennas are not painted inadvertently, as paint will affectan antennas performance.

General Once-Over

Go over all the switches and placards in the aircraft to make sure everythingis properly labeled and everything works as advertised. Also make sure fuses andor circuit breakers work properly. These things do occasionally quit simply fromold age or use.

Circuit breakers that have popped several times may need to be replaced, asthey may not be able to meet their amp rating under load. Do not install higherrated breakers, however, to cure a popping breaker. The wiring may not be ableto support the additional load.

In this era of GPS wonderboxes, its easy to ignore the other navcom gearuntil there is a problem with the GPS. Check out all the avionics, frequencies,etc., within the limits of the airport policies on communications, VOT check,etc. Include a check of speakers (which you may not normally use because of aheadset) and spare microphones used for backups.

Make sure transmissions both transmitted and received are clear, sidetone isworking properly, and squelch systems do their job without excess signalreduction. Radios sometimes work OK on some frequencies, and not at all well onothers higher or lower on the band, so a comprehensive check will help avoid asurprise while away from home and an unusual frequency is called for. Staywithin prescribed AIM rules for transmitter checks.

Even if you dont fly IFR, performing the VOR operational check outlined inthe AIM, Section 1-1-4 or 91.171 of the FARs for OBS operation, flag check,needle accuracy, etc., is a good idea for all pilots. This can be performed onthe ground at airports VOT equipped, or in flight otherwise. While these checkshave to conform to a schedule and recorded for IFR flight, annual checks shouldbe considered at minimum for all VFR only fliers.


You can also check your ELT, even though it should have been part of theannual inspection, we are aware of more than one instance where this has beenignored and assumed to be OK, or only the battery expiration date checked.According to FAR 91-207(d), ELTs must be examined once a year for properinstallation, operational problems, battery corrosion, and sufficient radiatedsignal. Normally this is done as part of the annual inspection.

Make sure there is no corrosion not only on the battery but also theconnector pins, and that the mount itself is secure and the ELT is secure in themount. Make sure the orientation is proper for crash activation, and that anycables have proper slack. You cannot legally move an ELT anywhere you like foreasier access without the proper paperwork approval from the FAA.

Operational checks for crash activation can be done by rapping with the palm(TSO-C-91 types, or by a rapid forward and reverse throwing-type motion onTSO-C91a type units). These checks are limited by FARs to the first five minutesof the hour and for only three pulses (beeps) of the system on 121.5.

Later TSOs, such as those for 406 MHz units spell out check procedures. Wedont recommend these operational checks be done by owners, but only to assurethat these checks are being done as required, rather than blown off.

One check that can be easily owner performed is using the ON or ELTactivation switch and listening on 121.5 for a strong signal. The test time andsignal length guidelines apply here also.

Installation of other avionics systems antennas can seriously impede the ELTantennas ability to send a strong signal, and those planes with new antennasare particularly important candidates for a thorough ELT operational and signalstrength check.

By the way, most IAs we have checked with as well as the FAA says there is noprohibition from an owner changing an ELT battery, provided no criticalstructure (for safety of flight) must be removed for access to the ELT. Itsnot specifically called out on the preventative maintenance section of the FARs,but battery changing in general is allowed, and it does not limit that to thestarting battery. Its one of those gray areas.

Summing Up

As you can see, there are a great many areas that can easily slip by anannual-either as not specifically required or sometimes incompletely checkedas in the ELT. Knowing that your avionics and instrument systems are up to snuffsure can take some of the anxiety out of IFR (or even VFR) flying.

I know first-hand that these systems or components seem to break at the worstpossible time when you need them the most (Murphys Law). If you have personalawareness of the layout and condition, you are that much closer to eitheravoiding a problem in the first place or more quickly finding the problem whenit does occur.

If you dont want to do these checks yourself (which we think you should)for any reason, then by all means arrange with whoever is doing your annualinspection to be sure to add these checks to his list-and expect to pay forhis added time to do that which is above the minimum legal list (which is whatmost annuals are based on price and time-wise).

A good but potentially expensive alternative is to have a trusted avionicsshop give your plane the once-over annually if you fly IFR. Its money wellspent for peace of mind. Just dont hand them your credit card and say fix itwithout a thorough briefing to you of proposed fixes and costs.

Dont forget about making sure you have other recurring checks for IFRflown aircraft such as altimeter and pitot/static checks and biannualtransponder checks too.