The last trip I flew didn’t start out very smoothly. We were scheduled to fly from Japan to Hawaii with an evening departure.  The flight was long enough that we were manned with an extra pilot who had just finished the exterior inspection of the plane and came back to the cockpit followed by one of the local maintenance personnel. The mechanics, on their post-flight inspection, had found a discrepancy with the aircraft.

Maintenance Discrepancies

What do you do when that happens to you? If you found something mechanically wrong with the airplane that you were about to fly, what would be your next course of action? (Let’s make the assumption that you’re making a Part 91 flight rather than flying a charter or scheduled air carrier flight.)

You would probably ask yourself a few questions. For instance –  Is this item required to be operating for my flight? The answer to this question would depend on what kind of flight you are about to make – day or night, VFR or IFR and whether the item is on the list of required equipment for that type of flight, as listed in CFR 91.205. It would also depend on whether the item is listed in the airplane manufacturer’s list of required equipment or specified as required by any installed Supplemental Type Certificate (STC) modification or required by an Airworthiness Directive (AD). Lastly,  it would depend on whether or not the airplane you were about to fly has an approved MEL, or Minimum Equipment List that includes the item.

CFR 91.213 says that you cannot takeoff unless you have taken care of the inoperative item in one way or another.

What’s an MEL?

Airplanes are getting more and more complex with every iteration. Large transport category planes are filled with items that, if they become inoperative, have no real bearing on the flying ability of the plane. Let’s say, for example that an engine-driven generator failed for some reason. Without some sort of dispensation, if the generator could not be fixed, the plane would be grounded. Enter the MEL. The airplane manufacturer, operator and the FAA get together and look at each item in/on the airplane and decide whether or not it is actually necessary to have that specific item working to make a safe flight. If this happens to be a four-engine aircraft and the other three engine-driven generators can easily provide enough electrical power to operate the aircraft equipment, the MEL might say that although four generators are installed, only three have to be operational. Then the MEL would go on to give the specifics for the situation. It would list any flight crew procedures that would be required, such as ensuring after engine start that the remaining generators are all working normally. It would also list the specific procedures that the maintenance personnel would be required to perform to safely disable the generator and where to place placards in the cockpit to alert the crew to the discrepancy. It would also specify how long the generator would be allowed to be inoperative before it would have to be repaired or replaced, usually in a specific number of days or flights.

Any aircraft can be operated using an MEL system, though the complexity of setting up the maintenance program for a typical single-engine general aviation airplane generally does not warrant the effort. The MEL program is described in Advisory Circular AC-91-67, dated June 28, 1971.  The process involves visiting your local FAA FSDO (Flight Standards District Office) and obtaining a copy of the Master Minimum Equipment List (MMEL) that has been generated for your type of aircraft. You and your maintenance adviser/mechanic would then compare that MMEL with the equipment in your specific aircraft and make appropriate additions or subtractions and develop procedures specific to your aircraft. This MEL modified for your aircraft would then be submitted to the FSDO for approval. I would imagine it would take several iterations before an MEL was finally approved but once it was, you would be given a letter of authorization to operate your aircraft (specified by serial number and registration) using the MEL process.

What if it isn’t listed in the MEL?

Ouch! You just went through that whole process and have an approved MEL for your plane and now something not listed in the MEL has broken. Short answer: You’re grounded until you can fix it, whether you need it or not. If the item is not listed in the MEL with an associated maintenance procedure, then the item has to be fixed before you can make your flight.

And that’s why most light planes don’t have an MEL program. Without an MEL, if something breaks, you first determine if it’s required by the regulations, STCs or ADs. Then you, as the PIC determine if the proposed flight can be safely completed without the equipment. If you can, then your mechanic can either remove it or safely disable it, placard it inoperative, put the appropriate words in the maintenance records and you’re good to go. You can then make the flight with the item inoperative, with the requirement specified in CFR 91.405 that the item be repaired or permanently removed at the next required inspection (annual or 100-hour).

Did we get to the beach?

Yes, we did, but not on that airplane. The mechanic had found a 3/4″ crack in the aircraft skin where one of the bathroom exhaust vents exits the side of the fuselage. A long discussion followed which was hampered by language and the need for decisions to be made in the U.S. and then relayed to Japan. Not a very efficient system in this situation. Luckily this particular aircraft was equipped with a satellite phone system. The Captain was able to talk directly with the flight dispatcher and maintenance control. The end result was that the aircraft was grounded and we waited for another flight to arrive so that we could take their plane. We got to have our umbrella drinks on the beach, but it was a few hours later than we had planned.

Related Links:

Advisory Circular 91-67, Minimum Equipment Operations for General Aviation Operations under FAR Part 91.

CFR 43-11, Records for Inspections Conducted Under Part 91.

CFR 91-205, Instrument and Equipment Requirements.

CFR 91-213, Inoperative Instruments and Equipment.

CFR 91-405, Maintenance Required.