Aircraft Maintenance: Deferred maintenance

Backup instruments, ADFs, and lorans were frequently out of service in the worn-out rental aircraft that fit my budget at the time. I was probably three years into flying when I had my first chance to use an autopilot that wasn’t marked as inoperative. It always amazed me that people would go to the trouble of making those nice “INOP” placards, rather than just fix what was broken, but I was young and naïve in the costs of aircraft ownership.

So, all of this convenient placarding begs the question: When is it OK to simply mark something inoperative rather than fix it?

The answer can be found in 14 CFR 91.213, "Inoperative instruments and equipment," which is largely about something called a minimum equipment list (MEL). An MEL is defined in Advisory Circular 91-67 as a precise listing of instruments, equipment, and procedures that allows an aircraft to be operated under specific conditions with inoperative equipment. It is a document that must be created for a specific aircraft and must be approved by the FAA Flight Standards District Office (FSDO). For many aircraft, the FSDO has a catalog of master minimum equipment lists (MMEL) for the aircraft type. These are generic lists that an owner or operator can customize to their specific aircraft and use as the basis for their unique, “FAA Approved” MEL.

If you have an approved MEL for your aircraft, you have a basis for simple decisions about what equipment may be inoperative and what equipment may not. That said, if you don’t have an MEL for your aircraft, the federal aviation regulations have you covered under 14 CFR 91.213 Part d, which reads:

(d) Except for operations conducted in accordance with paragraph (a) or (c) of this section, a person may takeoff an aircraft in operations conducted under this part with inoperative instruments and equipment without an approved Minimum Equipment List provided—

(1) The flight operation is conducted in a—

(i) Rotorcraft, non-turbine-powered airplane, glider, lighter-than-air aircraft, powered parachute, or weight-shift-control aircraft, for which a master minimum equipment list has not been developed; or

(ii) Small rotorcraft, nonturbine-powered small airplane, glider, or lighter-than-air aircraft for which a Master Minimum Equipment List has been developed; and

(2) The inoperative instruments and equipment are not—

(i) Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated;

(ii) Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List for the kind of flight operation being conducted;

(iii) Required by § 91.205 or any other rule of this part for the specific kind of flight operation being conducted; or

(iv) Required to be operational by an airworthiness directive; and

(3) The inoperative instruments and equipment are—

(i) Removed from the aircraft, the cockpit control placarded, and the maintenance recorded in accordance with § 43.9 of this chapter; or

(ii) Deactivated and placarded “Inoperative.” If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with part 43 of this chapter; and

(4) A determination is made by a pilot, who is certificated and appropriately rated under part 61 of this chapter, or by a person, who is certificated and appropriately rated to perform maintenance on the aircraft, that the inoperative instrument or equipment does not constitute a hazard to the aircraft.

If you followed all of that, “Congratulations, the FAA probably has a job opening with your name on it!”

For the rest of us mere mortals, it boils down to the following.

If you do not already have an MEL for your aircraft, you may fly with certain instruments inoperative, provided that:

• The inoperative instruments are not basic VFR-day instruments that were required by the FAA to get the aircraft certified in the first place (such as a tachometer, airspeed indicator, compass, etc.);
• The inoperative instruments are not listed in the aircraft’s equipment list or Kinds of Operations List, such as stall warning horns or other items listed in the type certificate or items required for the type of flying you are about to do (such as lighting if you are about to fly at night);
• The inoperative instruments are not required by an AD;
• The inoperative instruments are deactivated, clearly marked as inoperative, and recorded in the maintenance records.

So, there you go, if the estimate for repair to that backup generator comes in near the cost of a semester’s tuition for your kids, you have options. Just be sure to follow the proper procedures and apply good judgment to ensure that you are not compromising safety for the sake of saving a little money. Happy flying!