Curious if someone could walk me through a few real life scenarios for how an MEL works for the pilots, as handed off to the Maintenance team.

Like, a light goes, off, and the pilot opens up a binder or an ipad with a PDF on it? And then...errr...what happens next.

And then, let's assume its something that can be placarded...how does that work with the maintenance teams. Is that recorded anywhere for the pilot and for the maintenance team? Does anyone keep track of the inoperative items on a MEL?

Trying to wrap my head around how it works from tip to tail.

For a light, for example a navigation light that was U/S on the walk around, advise the mechanic/engineering and write it in the techlog.

The mechanic/engineering will carry out there procedure to try and repair the item, if it cannot be repaired (often parts are not right next to the aircraft) they will liaise with the pilots to see if they are willing to MEL the item, more often than not, the answer is yes.

Engineering carry out there procedures, which can include disabling NAV SYS 1 via C/B and then raise an MEL in the techlog. This MEL has a number. When they raise the MEL it has a category, meaning the number of days/hours/cycles it is allowed to be differed for. They include a reference to the MEL item number that the flight crew can lookup.

When the pilots lookup the MEL, it might say the repair interval is 10 days, there are 2 systems installed, 1 is required. In the case of a NAV night on system 1 being inop, engineering might raise the MEL that says NAV SYS 2 light operational. The procedure in the MEL says it is placard, so a sticker is placed next to the NAV light selector, and the MEL will say something like during cockpit preparation place switch in position 2.

The MEL remains "OPEN" it it remains in the tech log as well as the maintence planning system until it is cleared, normally by replacing the bulb that was blown on SYS 1.

When the close the entry, it is actually two entries, one to replace the bulb (so the trace the parts on/off), the other to close the MEL to remove the item from the techlog and from the maintenance planning system..

For starters, typically a light won't "go off" to make us dig into MELs. If a light goes off (most likely accompanied by an ECAM/EICAS message) we apply the appropriate procedure, electronic or paper. MELs can only be applied before dispatch (defined as park brake off). After that, they are not technically applicable (but often referred to for information). For example, if a reverser goes inop in flight, we don't apply the MEL for it.

The way it works, a piece of kit will become inop and this is discovered either with a light going off or an inspection or something else. This will go in the tech log. The engineers will be able to fix it or not, depending on time and parts constraints. If it can't be fixed on time, the piece of kit will be MELd as appropriate.

When we get to the aircraft, one of the first items on the agenda is to review the tech log. Any MEL items will be listed there. We look up every MEL item and review how it affects us. An inop brake would affect takeoff and landing distance, so it would be a factor in performance calculations. An inop APU would require a ground start cart, and ground power and air to be available at the destination. An inop nav light would require us to set the switch in order to use the other nav light. Different MELd items might require different supplemental procedures.

Some items require a placard. Others do not. Some affect ETOPS dispatch capability. Some affect landing distance. They come with varying acceptable inop times, from a few days to several months.

As Starlionblue pointed out the MEL is something that applies before departure, not in flight. Typically when I show up to fly any MELs (or, more correctly, deferred maintenance items) will be listed on the flight release and in the aircraft logbook. If dispatch is in a good mood that day they might print out the relevant page(s) from the MEL, otherwise I'll look them up myself to determine any operating limitations. Performance penalties are applied by dispatch as part of the planning process. Occasionally we (the crew) will find inoperative items during preflight in which case we notify dispatch, dispatch notifies maintenance and maintenance either fixes or defers the item.

When items fail in flight we have a book called the QRH (Quick Reference Handbook) which contains all of the non-normal procedures as well as (rough) performance information. On the 737 the QRH is pretty intuitive: Let's say the #1 generator LOW OIL PRESSURE light comes on in flight. You pull out the QRH, look up LOW OIL PRESSURE (generator) and follow the procedure. If the inoperative items warrants a diversion the checklist will tell you to do so, otherwise it is assumed that you will continue to your destination.

The MEL is not relevant in flight but becomes very relevant after you land because certain items are not deferable, and for those of us who fly in remote areas this can be a factor in deciding whether or not to continue the flight. A few weeks ago I lost two fuel pumps (one in each tank) simultaneously in flight due to what turned out to be a controller failure. While the QRH checklist prescribed no special action (each tank has 2 fuel pumps which meant one was still working per tank), I consulted the MEL and learned that our specific combination of failed fuel pumps was not deferable. As our planned destination was in a very remote location with no passenger flights scheduled for a few days, the company and I agreed to return the airplane to base.

An example of how the MEL can be referred to but not technically applied after dispatch.

If you get certain engine fault messages, but the engine is still running, while taxiing out, you should apply the ECAM procedure. But in many cases the procedure is nothing else than "crew awareness". Ok, we are aware. Dig into the MEL and it tells you "no dispatch" with this fault... So what do you do? While you can technically continue, a prudent crew would ask ATC to stop somewhere and ring up engineering so they can weigh in.

If you get it in flight, considerations are of course also different. "No dispatch" in the MEL doesn't help you much because you can't exactly return to the bay at this point.


To ArcticFlyer's point, the maintenance log is not just full of MELs. The relevant section is "deferred maintenance items", some of which have an MEL reference. The MEL is a guide as to the effects of the deferred maintenance item. Many items don't have an MEL (or CDL) reference.

On the A330, an abnormal (e.g. a broken piece of kit) will either be sensed and result in an ECAM procedure that you follow on the screen, or be not sensed and you have to dig into the QRH for it. On the A350, the not sensed procedures have been moved from the QRH into ECAM, and are accessed using the "ABN" button on the ECAM control panel. Electronic or not, it's all the same basic concept.

Examples of sensed abnormals: Engine failure, hydraulic low pressure, hot brakes... Examples of not sensed abnormals: Tire damage suspected, Volcanic Ash Encounter, Fuel Jettison.

Starlionblue wrote:

The MEL is a guide as to the effects of the deferred maintenance item. Many items don't have an MEL (or CDL) reference.

The MEL only contains systems or components that may be inoperative. Any structural damage like dents or scratches, or damaged fan blades, worn tires etc. need other references for a deferral, for example the AMM or SRM. Maintenance can't just decide out of the blue what to defer and for how long.
When there is a defect relevant to the airworthiness of the aircraft and there is no approved document for a deferral the engineering department or manufacturer has to come up with a solution. Otherwise the aircraft is AOG until the defect is repaired.

MEL Preamble wrote:

The MEL contains only those items of airworthiness significance which may be inoperative prior to dispatch, provided limitations and appropriate procedures are observed. Equipment obviously basic to airplane airworthiness such as wings, rudders, flaps, engines, landing gear, etc. is not listed and must be operative for all flights.
It is important to note that: ALL ITEMS WHICH ARE RELATED TO THE AIRWORTHINESS OF THE AIRPLANE AND NOT INCLUDED ON THE LIST ARE AUTOMATICALLY REQUIRED TO BE OPERATIVE.
Equipment obviously not required for safe operation of the airplane such as galley equipment, passenger convenience items, etc. is not listed.

The MEL is a customized document that has to be approved by the authorities. There is a Master MEL issued by the manufacturer and every operator can modify this list to their needs. However the customized MEL can only me more restrictive, never less restrictive, than the MMEL.

Here's a story:
I was a line mechanic once upon a time. We has a little fold out table in the jetway so that we could do paperwork out there and give the crew access to the flight deck. It was an international flight at a US domestic airline. The crew came down the jetway dragging their bags. The Captain asked, "How's the jet?" I said, "Its fine, only one MEL, and its a non-event." He said, "Well, we'll have to evaluate it and decide." I replied, "Well the book says we can go." He said, "My book over-rules your book. We'll take a look."
I learned something that day. The MEL is written for a "normal" or "routine" day. There can be circumstances which cause an otherwise appropriate MEL to not be applicable in THAT situation. Example? There are many. Here is one: putting an anti-skid on an individual wheel on MEL. This entails a performance restriction. Lets say you are going to an airport with a long runway, say 12000 feet and a short runway, say 8000 feet. Lets say that the long runway is closed per NOTAM (you have to read your NOTAMs!), and there is light rain falling. An 8000 foot wet runway with a single wheel anti-skid inop may entail a performance restriction. We may have to leave people and/or bags behind. Maybe its a tanker leg and the fuel has already been uplifted, how long with the defuel take? Do we have parts, is it quicker to fix than defuel? Can we call the airport authority and see if the long runway can be opened for our ETA? The point of this example is that there are many potential scenarios, and many potential ways to address the concern. Just because it is possible to add the MEL in the MEL book, it doesn't mean that is wise or utile to do so.

Another time a similar conversation ensued. The Captain asked, "What is the item that is on MEL?" I said "TCAS." He said, "Well we need that, we can't go without that can we?" I replied, "Captain, its not even installed on all the airplanes yet....sure we can go without it." And yet, there are systems that, if installed, have to be working. That was not the situation in this case. But TCAS was so useful to pilots, they wanted it. All the pilots were early adopters. Out on the tracks, they could see the guys around them, so that if they needed to climb or descend for turbulence (admittedly hard to get a clearance on the tracks on HF), they could see if there was anyone around them, they knew before they asked if ATC was likely to issue the clearance. I learned something else, good systems don't have to be "sold" to users, they "sell" themselves by their utility.

I once got an airplane with 8 MELs and 8 orange inop stickers - all 8 MELs were for cockpit lighting - oh no big deal...they're just light bulbs.... we flew the plane all day without any issues until....

the sun set...

after the sun set the cockpit was dark - each light that was MEL'd was a light inside each one of our steam-gauge instrument gauges - now were were flying partial panel with no working lighting on my and the FO's airspeed indicator, altimeter, vertical speed indicator, and turn coordinator - all we had were the CRTs for the attitude indicator and EHSI/EADI. We completed the leg with the FO holding the emergency flashlight over my head illuminating the instrument gauges, which got dimmer and dimmer the longer we flew - we went thru the FO's flashlight, my flashlight, and were down to the two emergency flashlights by the time we landed...

That's the last time I ever took cockpit lighting MEL's lightly.

Flashlights - another term for dead 2 D-cell battery canisters.

The old B727 “gotcha” was an MEL-able dispatch with a #3 generator inoperative, approved by the MEL, but rarely taken and great oral question. The problem being with a #1 and #2 engine loss, no rudder, uncontrollable single-engine landing on #3. EA instructor gave us this problem when all the other stuff had been done. I saw it on the line, captain asked what I thought. He with 25,000 hours on it knew the answer, but wanted to see if his new SO, knew it,

Woodreau wrote:

I once got an airplane with 8 MELs and 8 orange inop stickers - all 8 MELs were for cockpit lighting - oh no big deal...they're just light bulbs.... we flew the plane all day without any issues until....

the sun set...

after the sun set the cockpit was dark - each light that was MEL'd was a light inside each one of our steam-gauge instrument gauges - now were were flying partial panel with no working lighting on my and the FO's airspeed indicator, altimeter, vertical speed indicator, and turn coordinator - all we had were the CRTs for the attitude indicator and EHSI/EADI. We completed the leg with the FO holding the emergency flashlight over my head illuminating the instrument gauges, which got dimmer and dimmer the longer we flew - we went thru the FO's flashlight, my flashlight, and were down to the two emergency flashlights by the time we landed...

That's the last time I ever took cockpit lighting MEL's lightly.

Flashlights - another term for dead 2 D-cell battery canisters.

That brings up another point about "use and management of the MEL." Constant monitoring for downline implications is something that needs to be handled at every airline. The dispatcher that accepted that MEL wasn't looking down line far enough to see that the airplane was going to be flying after dark before hitting a mtc base. He/she was just looking at his/her flight. I've seen this with International airplanes flying around domestically also. The domestic dispatcher accepts an MEL, but later in the day that airplane goes International and the MEL is not approved for overwater or ETOPS or whatever. The airplane ends up somewhere where there are no parts or no trained mechanic to clear that MEL prior to going International. Every airline should have processes and awareness of looking more than one chess move ahead. Unfortunately, some managers snap people's heads off when they point out that they are painting the airline into a corner. Its bad when the MANAGERS are only thinking one flight at a time, but sadly I've seen it happen.

Really, I'm sure with all the expertise on this board we could write a book. The original poster may not have realized how central "use and management of the MEL" is to the proper function of an airline. MEL management is critical, for safety, efficiency, everything.

SteelChair wrote:

Every airline should have processes and awareness of looking more than one chess move ahead. Unfortunately, some managers snap people's heads off when they point out that they are painting the airline into a corner. Its bad when the MANAGERS are only thinking one flight at a time, but sadly I've seen it happen.

In my experience no airline is capable of the forethought you describe. It's a nice idea though!

SteelChair wrote:

Here's a story:
I was a line mechanic once upon a time. We has a little fold out table in the jetway so that we could do paperwork out there and give the crew access to the flight deck. It was an international flight at a US domestic airline. The crew came down the jetway dragging their bags. The Captain asked, "How's the jet?" I said, "Its fine, only one MEL, and its a non-event." He said, "Well, we'll have to evaluate it and decide." I replied, "Well the book says we can go." He said, "My book over-rules your book. We'll take a look."
I learned something that day. The MEL is written for a "normal" or "routine" day. There can be circumstances which cause an otherwise appropriate MEL to not be applicable in THAT situation. Example? There are many. Here is one: putting an anti-skid on an individual wheel on MEL. This entails a performance restriction. Lets say you are going to an airport with a long runway, say 12000 feet and a short runway, say 8000 feet. Lets say that the long runway is closed per NOTAM (you have to read your NOTAMs!), and there is light rain falling. An 8000 foot wet runway with a single wheel anti-skid inop may entail a performance restriction. We may have to leave people and/or bags behind. Maybe its a tanker leg and the fuel has already been uplifted, how long with the defuel take? Do we have parts, is it quicker to fix than defuel? Can we call the airport authority and see if the long runway can be opened for our ETA? The point of this example is that there are many potential scenarios, and many potential ways to address the concern. Just because it is possible to add the MEL in the MEL book, it doesn't mean that is wise or utile to do so.

Another time a similar conversation ensued. The Captain asked, "What is the item that is on MEL?" I said "TCAS." He said, "Well we need that, we can't go without that can we?" I replied, "Captain, its not even installed on all the airplanes yet....sure we can go without it." And yet, there are systems that, if installed, have to be working. That was not the situation in this case. But TCAS was so useful to pilots, they wanted it. All the pilots were early adopters. Out on the tracks, they could see the guys around them, so that if they needed to climb or descend for turbulence (admittedly hard to get a clearance on the tracks on HF), they could see if there was anyone around them, they knew before they asked if ATC was likely to issue the clearance. I learned something else, good systems don't have to be "sold" to users, they "sell" themselves by their utility.

Excellent points. In context, we dispatched once with a defect that made EGPWS inop. No big deal since it was daylight VMC with fine weather all the way there and back. On a dark and stormy night, you might not do the same, even if it is legal.

Jfermeee wrote:

Curious if someone could walk me through a few real life scenarios for how an MEL works for the pilots, as handed off to the Maintenance team.

Like, a light goes, off, and the pilot opens up a binder or an ipad with a PDF on it? And then...errr...what happens next.

And then, let's assume its something that can be placarded...how does that work with the maintenance teams. Is that recorded anywhere for the pilot and for the maintenance team? Does anyone keep track of the inoperative items on a MEL?

Trying to wrap my head around how it works from tip to tail.

MELs are different than Placards, at this airline.

Flight crew writes up item on aircraft computer system.
Message gets sent to maintenance.
Evaluation of said item gets done by maintenance, time to fix or put on MEL, or other deferral.
Maintenance performed entered into computer, along with fix or deferral status.
If item is fixed or deferred, computer system logs it into aircraft log.
A release is sent to aircraft printer, with all deferrals listed.
Release is maintenance release, aircraft is airworthy.
Some items that are deferable, can be refused by flight crew and maintenance due to circumstances.
Aircraft deferral is then fixed.
New aircraft release sent to aircraft.
Aircraft airworthy.

zeke wrote:

For a light, for example a navigation light that was U/S on the walk around, advise the mechanic/engineering and write it in the techlog.

The mechanic/engineering will carry out there procedure to try and repair the item, if it cannot be repaired (often parts are not right next to the aircraft) they will liaise with the pilots to see if they are willing to MEL the item, more often than not, the answer is yes.

Engineering carry out there procedures, which can include disabling NAV SYS 1 via C/B and then raise an MEL in the techlog. This MEL has a number. When they raise the MEL it has a category, meaning the number of days/hours/cycles it is allowed to be differed for. They include a reference to the MEL item number that the flight crew can lookup.

When the pilots lookup the MEL, it might say the repair interval is 10 days, there are 2 systems installed, 1 is required. In the case of a NAV night on system 1 being inop, engineering might raise the MEL that says NAV SYS 2 light operational. The procedure in the MEL says it is placard, so a sticker is placed next to the NAV light selector, and the MEL will say something like during cockpit preparation place switch in position 2.

The MEL remains "OPEN" it it remains in the tech log as well as the maintence planning system until it is cleared, normally by replacing the bulb that was blown on SYS 1.

When the close the entry, it is actually two entries, one to replace the bulb (so the trace the parts on/off), the other to close the MEL to remove the item from the techlog and from the maintenance planning system..

At my last airline and my current one no two entries needed. All log pages have a section at the bottom of the page for parts info you can close the original write up close the MEL with the parts change and put the parts info on the original page.

stratosphere wrote:

At my last airline and my current one no two entries needed. All log pages have a section at the bottom of the page for parts info you can close the original write up close the MEL with the parts change and put the parts info on the original page.

Ours is all electronic done on iPads. The iPads have a number of “personalities” that can be chosen from cabin crew, flight crew, engineering etc.

If I log a defect in flight crew mode, it has a mechanic clear it in engineering mode.

Data entry for parts off/on is done on the iPads, so is raising or clearing MELs, and other checks like weekly checks.

Engineering release the aircraft In engineering mode.

Flight crew review the aircraft status and then accept it in flight crew mode.

The iPads uplink all the data with the servers so the data on both the iPads and the servers is synced.

I was a Mechanic. Foreman, and Maintenance Controller at United we got rid of our logbooks and went to an electronic release where all the MEL's and Deferred items ae listed the maintenance release which includes all the maint history back 200 Hrs. The release has all the open Mel items and when a check comes due we have all the Deferred items and Carry forward (Non-MEL) listed the MEL's do not get extensions the Carry forward items might get one with an engineering concurrence.

Thanks everyone for your informative replies!