BizJet Minimum Equipment Lists: Why They’re Important

A Minimum Equipment List (MEL) is a standard, structured list documenting an aircraft’s equipment or systems which may not be working correctly but still allow an aircraft to fly safely under certain conditions.

MELs are used as a reference by both pilots and aircraft maintenance technicians, and they are part of the documentation carried aboard the aircraft.

Why is Your MEL so Important?

As mentioned, the importance of an MEL to a flight department manager lies in the fact that it allows you to dispatch an aircraft with some of the equipment inoperative. If there is a component that is inoperative and there’s the need to dispatch before it can be repaired, the presence of duplicate systems on the aircraft allows you to do so, owing to built-in redundancy.

“As an operator you want to be able to have as much leeway as possible, but at the same time you also want to operate as safely as possible,” Stewart D’Leon, Director of Technical Operations, NBAA, told AvBuyer.

In this two-part story we will cover the use of MELs in Business Aviation; consider why an MEL is important; focus on the specific Business Aviation requirements with regard to MELs; and think about the procedures for MEL development and training in a Business Aviation organization.

Jeremy Purry, Technical Author at Total AOC/Centrik notes that, as with commercial passenger operations, business aircraft have designated windows for departure and schedules to maintain.

“If something is found on an aircraft that is not working correctly, there is pressure to get the issue rectified to allow the aircraft to depart as close as possible to its planned departure time”, he says. 

“If an inoperative component is discovered, the MEL will inform the flight crew and engineering personnel if it is safe to take off, providing a structured way to assess the fault and determine the steps that must be taken – in line with all safety regulations – before making a decision to fly.”

While the MEL is a document that is developed by the operator, it is based on the Master Minimum Equipment List (MMEL), which is developed by the OEM. “The MMEL is a kind of overarching document that can be used by an operator to develop the MEL,” D’Leon explains.

“There are different ways to do that, but most important is that the MEL cannot be less restrictive than the MMEL. The MEL can contain additional restrictions, but it cannot be less restrictive.

“Moreover, if, for example, it is a requirement to have two VHF radios installed and one to dispatch, all the actions that need to be taken to dispatch with one will be stated, too, in the MEL,” D’Leon adds. “These actions are identified in the maintenance and operational procedures section.”

If an item is not in the MEL, it is not possible to dispatch with one inoperative. “If I have a VHF radio that’s inoperative and it is not listed in the MEL, it is not possible to dispatch the aircraft”, D’Leon explains. “However, there may be items that are not in the MEL, but are on a Configuration Deviation List (CDL) or a Non-Essential Furnishings (NEF) list.

“These additional documents complement the MEL and allow for dispatch with inoperative items that may not be listed in the MEL.”

Specific MEL Requirements in Business Aviation

Although MELs are not specific to Business Aviation, there are some aspects of the MELs that are different for Business Aviation compared to other sectors (such as the airlines). One such aspect is that often the Business Aviation operator has greater ability to fix the faulty component or the system.

“For an air carrier that provides a scheduled service, there tends to be less flexibility,” D’Leon notes. “So, if there is a way for them to quickly fix the inoperative component, they will do it. Otherwise, they will defer it until they can get that aircraft home, usually that evening, or until the next scheduled maintenance.

“By comparison, Business Aviation organizations generally have flexible schedules that allow them to repair inoperative items prior to dispatch, and generally do not get into the MEL as often. Business Aviation operators primarily use the MEL as a resource to dispatch the aircraft from a remote location to their home base for repairs.”

Modern aircraft do not regularly break down or suffer significant system or equipment failure, so a business aircraft’s MEL document often remains unused for considerable periods of time.

“Due to the significantly higher number of flight hours carried out by a commercial airliner, the MEL may be used more frequently owing to more equipment wear,” notes Purry.

“In Business Aviation, aircraft do not fly as often, so wear and failures are far less frequent. 

"However, because of this reduced usage other problems may occur – an MEL will therefore most likely be required if an issue has arisen when the aircraft has landed at a smaller airfield, particularly one with no hangars or engineering support.

“In this case, the pilots would need to refer to the MEL to ascertain whether the aircraft is able to depart,” reflects Purry.

And so it is important that a Minimum Equipment List is carried and kept up-to-date for every business aircraft. How can you develop an up-to-date MEL in your flight operation, and what training is recommended relating to the MEL?

We’ll discuss these important questions next month. Stay tuned!