Well, it depends.
While the regulations generally require that all instruments and equipment installed aboard the aircraft be in working condition, it may be possible to operate an aircraft with a piece of equipment not working if it falls within the scope of FAR 91.213 or the aircraft is operating with a Minimum Equipment List.
FAR 91.213 allows certain Part 91 operators to fly an aircraft with inoperative instruments or equipment but it is limited to aircraft operating in a non-turbine powered, small airplane. A small airplane is defined as one that has a maximum certified takeoff weight of 12,500 pounds or less. But there are additional limitations.
The inoperative instruments and equipment cannot be part of the VFR-day type certification requirements or indicated as required on the aircraft’s equipment list or the aircraft’s kinds of operations equipment list for the kind of flight operation being conducted. The equipment also cannot be required by FAR 91.205 which describes the bare minimum for airworthiness, or any other rule of Part 91. The inoperative components also cannot be required to be operational by an airworthiness directive.
The aircraft’s equipment list, or kinds of operations equipment list, can be found in the Pilot’s Operating Handbook.
Finally, a pilot or certified mechanic must determine that the inoperative instrument or equipment does not constitute a hazard.
If it is determined the flight can be conducted safely under the guidance of FAR 91.213, the inoperative instruments and equipment must be removed from the aircraft, the cockpit control placarded, and the maintenance recorded. Alternatively, the equipment can be deactivated and placarded inoperative. If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in the aircraft maintenance logs.
MINIMUM EQUIPMENT LISTS
For aircraft that are unable to utilize the relief for inoperative instruments or equipment contained in FAR 91.213, such as jet aircraft or any aircraft operated as a certified air carrier under Part 135 or 121, the only option for relief is to utilize a Minimum Equipment List (MEL). An MEL is a precise listing of instruments, equipment, and procedures that allows an aircraft to be operated under specific conditions with inoperative equipment.
The MEL is developed from the Master Minimum Equipment List (MMEL) which is produced by the aircraft manufacturer and ultimately approved by the FAA. An operator’s MEL may be identical to the MMEL but it does not have to be. If it differs, the MEL can never be less restrictive than the MMEL which is why many operators choose to simply adopt the MMEL.
When the individual operator’s MEL is approved and authorized by the FAA, it then becomes a Supplemental Type Certificate for the aircraft and must be followed at all time. It is worth noting, that even if an aircraft/operator is eligible to utilize the relief of FAR 91.213 for inoperative instruments and equipment, you may choose to seek approval for an MEL. But once the MEL is approved, you must always abide by the MEL and are not permitted to revert back to FAR 91.213.
The FAA has MMELs available for most of the type-certificated aircraft in use today. They can be found with the FAA’s Dynamic Regulatory System page. Certain instruments and equipment are not allowed to be included in an MEL. For example, instruments and equipment that are required by airworthiness standards.
An MEL is intended to permit operation with inoperative instruments or equipment for a limited period until repairs can be accomplished. The MEL also may establish conditions for operation with inoperative equipment. When inoperative equipment is discovered, the regulations require that it be reported via a proper entry in the aircraft maintenance records. The item is then repaired, or deferred for repair, but must also be deactivated and placarded inoperative by an appropriately certificated technician.
MEL conditions and limitations do not relieve the operator from determining that the aircraft is in condition for safe operation with items inoperative, and the deactivation of one inoperative instrument should not degrade or negate the performance of any other instruments or equipment.
Whether you are a Part 91 operator or a commercial operator, an FAA operations inspector will be the primary FAA official responsible for the overall process of evaluating, and approving an MEL document.
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