Suppose you are on a day VFR flight and you are testing your aircraft lights. If you discover that the bulb for one of your nav lights is blown, then you can turn the switch off and tape it off, placard it as inop, and fly anyway. However, if you don’t placard it, my understanding is that you are not legal to fly, even if it is day VFR and you leave the switch off.

My question: should you avoid testing unnecessary equipment? Presumably if you did not test the nav lights during your preflight (not intending to use them) then you never knew they were broken, therefore you didn’t need to turn off and placard as inop. What is best-practice here? My question is specifically about nav lights, but I am also interested in other optional equipment (eg an autopilot).

(This is in the USA as a Part 91 flight.)

  • $\begingroup$ What is the deal with placarding it? Putting a sticker with "inop" written on it won't take more than few seconds, will it? And at least you know it needs to be fixed, so you don't get stuck next time you want to go flying and actually need it. $\endgroup$
    – Jan Hudec
    Dec 15, 2015 at 10:50

2 Answers 2


The best practice is to pre-flight everything for every flight:

  • If you have different pre-flight procedures for different situations then sooner or later you'll use the wrong one and miss something that you should have found. Consistency is really helpful in procedures.
  • Even if something isn't needed for the flight, checking everything gives you an accurate picture of the state of the aircraft. One broken light is probably just a light bulb, but 3 broken lights and inop pitot heat may be a more serious electrical problem. If you don't know the state of the aircraft then you can't make informed decisions.
  • Plans change. You might set off for a day VFR flight on a clear, sunny day intending to be home hours before sunset. But if the weather changes quickly or you get delayed then your flight home might have to be night VFR or IFR. If you have equipment issues that restrict your options then it would be best to know that before you depart.

There's nothing wrong with flying with inop equipment provided that you know about it, you've complied with the rules in 91.213 on minimum required equipment and deactivating and placarding, and you've made a conscious assessment of the risk. But not inspecting the aircraft properly or deliberately ignoring inop equipment is a really great way to put yourself in an "up there wishing you were down here" situation.

And from a regulatory point of view, if you don't preflight properly then you're probably in violation of 91.103 ("become familiar with all available information concerning that flight") and of course 91.13 ("No person may operate an aircraft in a careless or reckless manner").

  • 1
    $\begingroup$ Please note that you can't defer everything. Some items are required by basic regulations, the aircraft type certificate, or the specific operation. $\endgroup$
    – nexus_2006
    Dec 15, 2015 at 16:44

It is the job of the pilot in command to verify the aircraft is in an airworthy state before flight. If you chose to not test "optional" equipment you would still be illegal if that equipment was inoperative. You are required to follow 91.213 if that equipment is inoperative whether or not you found out about it.

  • $\begingroup$ In the case of a light bulb, who's to say that it wasn't working fine the last time it was used? Or even that it worked when checked at the beginning of the day, but "now" when turned on, it burned out? Things work fine right up until they don't... $\endgroup$
    – Ralph J
    Dec 15, 2015 at 4:29
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    $\begingroup$ @Ralph J choosing not to do part of the preflight to avoid finding out about a malfunction is a hazardous attitude.... Invincibility - It won't happen to me. $\endgroup$
    – wbeard52
    Dec 15, 2015 at 4:50

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