What is the HELL is a MEL?aircraft mechanic MEL

Most aircraft mechanics heard the term MEL (pronounced em-ee-el) before. If you are new to aviation maintenance, you may be a little confused about what it exactly is. This is a general guide to help aircraft mechanics use the MEL to their advantage.

The MEL, or minimum equipment list, is an approved document from the FAA.  Companies operating under a part 121, 135 or even 91 use an MEL list. This is a list that allows the aircraft to be operated with something broken. Of course we are not talking someone major here, but perhaps a flight instrument back-lighting.  The MEL list each component that CAN be MELed. Obvious items such as the wing and rudder cannot be MELed.

Each item listed in the MEL has a different category, A,B and C. These are important because it lets you know how long the item can be INOP for. Category A is which ever is listed on the MEL. Honestly I have never seen a Category A so lets move on to cat B and C. Category B is good for 72 hours (3 days) and cat C is 240 hours (10 days).  This gives you time to order parts and tooling that might be required to fix the aircraft. Keep in mind that extensions are available however you must typically show you a good reason. Something like, “part ordered but not available, could not acquire tooling because company is too cheap to purchase more special tools” or something like that.  Again, typically this request gets sent into the compliance guy who asks the FAA for an extension.

Class II MELs – Non essential Furnishings

There is also a process to MEL or defer maintenance for items NOT in the MEL. This is called a Class II MEL. These items have to be things like window dressings or items that are obvious not safety problems but also not listed in the MEL because of their nature. “Chipped paint” would be a good class II MEL. Class II MELS, or NEF (Non Essential furnishings  At my company, class II MELs are not deferred under the authority of the A&P license, it is instead under the operators certificate. What this means is that I simply cannot Class II MEL a broken interior trim piece, I must first gain approval from a high authority within the company.  Items often are listed in a Class II NEF program within the company.



Get to Know the MEL

When ever something is broken, first thing I do is check the MEL. If it can be deferred, I will deffer it and get the aircraft back in service. Then I have time to troubleshoot it later as I

INOP sticker
“INOP” sticker

order parts and tooling. Do not try to memorize the MEL, it does get changed through revisions. Just because something seems like it can be deferred does not mean that it is. You must double-check the list.

I use the MEL to my advantage. One cold winter night, I get called into work because the pilot reported the heater not working.  At this point in my career, I was a mechanic on a helicopter for an EMS outfit. So I crawl out of bed and go into work and find that the heater is indeed inop, so I placed it on deferral as per the MEL. The pilot is concerned because they cannot fly with it being so cold, and the aircraft should NOT be returned to service because it is indeed “broken”. I had to explain that the aircraft is airworthy, it is the weather that is the problem, not the aircraft. Essentially, the aircraft was grounded due to weather, not the heater.

Another thing to remember, that the pilot in command will make all final decisions one whether they will fly or not. Even if the item is placed on MEL legally, they can refuse to fly the aircraft because they are uncomfortable with the item being INOP. That is not OUR problem. I often times tell the pilot, “I frankly don’t care whether you fly it or not, the aircraft is airworthy, the item is on deferral per MEL. We are legal.” Pilot not wanting to fly is not my problem.  Sometimes their concern is valid. Case in point, the N1 gauge to one of my engines can be INOP as per the MEL. The pilot has no idea how fast the N1 is spinning. The N1 speed is used in a few emergency procedures and not knowing what the speed is could be dangerous. All I can tell them is that the aircraft is airworthy per the MEL and I have parts on order.


Using the MEL

Company guidelines (GOM) will often times have procedures on how to properly use the MEL. They may even have an example of verbiage on what should be put into the log book.  There must be something placed in the discrepancy area of the log book, and the corrective action is something like “item is INOP,  Item is differed In accordance with  MEL….”

As you can see, the MEL can be used to your advantage in keeping the aircraft up. In all cases, make sure you review all company guidelines before attempting to MEL an item. Not following proper procedures can get people in trouble. Remember, you are attempting to operate an aircraft with a known problem, however small it may be, it is broken and documented in the aircraft log. This means you must very carefully follow all of the companies rules while placing anything on MEL. I always,ALWAYS have the pilot review my item on MEL and make sure they agree with what I have done. It is there certificates on the line as well.


aircraft mechanic MELIn the example above, we can see that this page is pertaining to the air-conditioning (ATA code 21 ). The list then breaks down each item within that system that can be INOP. Note that all of these on this page are CAT C or a 10 day MEL which is the kind I like. 120 days are better but rare for me.  Also, keep in mind that if there is an (M), than there is a maintenance function required. Other items can be MELed by the pilot without a mechanic in most cases, however, typically the (M) means a mechanic needs to do this task, such as “deactivated circuit” which means putting a zip tie on the pulled circuit breaker so the pilot cannot reset it.  Also, in the beginning of all MELs, it states that INOP items will be placarded with a “INOP” sticker. This can be any small label with the words “INOP” on it. When possible, place it next to the broken item’s switch.


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