Danh Sách Thiết Bị Tối Thiểu (MEL: Minimum Equipment List)

What Is a Minimum Equipment List?

A Minimum Equipment List (MEL) is an aircraft-specific regulatory document, approved by the relevant aviation authority (FAA or EASA), that allows an operator to dispatch an aircraft with certain inoperative equipment under defined conditions. The MEL is derived from the Master Minimum Equipment List (MMEL) established by the aircraft manufacturer and approved by the certificating authority, but is customized for each operator's specific configuration and operations.

The MEL is a critical safety document: it defines the minimum standard of airworthiness below which an aircraft may not depart. Each MEL item includes a dispatch condition (O-item: crew procedure required; M-item: maintenance action required), a rectification interval (A: 1 flight, B: 3 days, C: 10 days, D: 120 days), and the number of required operational items.

How It Works

When a discrepancy is discovered during pre-flight inspection or en route, the flight crew and maintenance personnel consult the MEL to determine whether the aircraft may continue in service. The process follows a structured decision tree:

• Is the item in the MEL? If not, the aircraft must be grounded until the item is repaired (all equipment must be operative unless specifically listed in the MEL).
• Dispatch conditions: O-items require specific crew procedures (e.g., autopilot inoperative — crew must demonstrate manual flying proficiency within recency requirements). M-items require maintenance actions (e.g., securing a circuit breaker open with a collar).
• Rectification intervals: Category A items require repair before the next flight. Category D allows 120 calendar days deferral — common for cosmetic or redundant items with no safety impact.
• Type certificate linkage: The MEL is part of the type certificate data and must reflect the aircraft's actual configuration. Modifications that add or remove equipment require MEL revision.

Key Examples

A Boeing 737-800 with one of its two windshield wiper motors inoperative would consult MEL item 30-11-1 (Windshield Wiper System). The MMEL typically permits dispatch with one wiper inoperative under Category C (10-day rectification), subject to the condition that flight into known or forecast icing conditions is prohibited. For an Airbus A320, an inoperative pack (air conditioning and pressurization unit) is MEL item 21-00-1: one pack may be inoperative for up to 3 days (Category B) with altitude restrictions and flight time limitations.

Aircraft Examples

• Airbus A320: MMEL contains approximately 2,400 items across all aircraft systems; operator MELs are typically 70–80% of that scope.
• Boeing 787-9: The more-electric architecture (replacing hydraulic systems with electric) required new MEL philosophy for electric motor pump units and battery management systems.
• ATR 72-600: Regional turboprop MELs are often more restrictive than wide-body equivalents due to lower system redundancy.
• General Aviation (Cessna 172): Part 91 operators are not required to have an approved MEL; instead, they operate under the equipment requirements of FAR 91.205 and the aircraft's Kinds of Operations Equipment List (KOEL).