Inop

In 2017, AC 91-67 “Minimum Equipment Requirements for General Aviation Operations Under FAR Part 91” was canceled because it was “misaligned with the latest ICAO [International Civil Aviation Organization] standards,” and it was only late in 2023 that the replacement version (AC 91-67A) was officially published as effective.

The reason for this putative misalignment largely stems from the FAA’s practice of allowing Part 91 operators to apply for one of two different letters of authorization (LOAs) that allow use of an MEL: a D195 LOA that requires the operator to develop their own MEL specific to their airplane, or the popular D095 LOA that allows the operator to use the FAA-published master MEL (MMEL) as their approved MEL. Given the choice to go through the mostly pro-forma application to use an MMEL as an MEL or being faced with the time and expense of creating a custom MEL, it’s not surprising many operators prefer the D095 route.

Yet an ongoing controversy with European authorities nearly led to the extinction of the D095. At one point the FAA intended to cancel all D095s and require operators to re-apply for a D195, with commensurate work. Fortunately, the FAA is now indicating it will continue to issue D095 LOAs to Part 91 operators, and in AC 91-67A is taking a strong stance in defense of D095s, stating: “MEL approvals under LOA D095 meet the International Civil Aviation Organization (ICAO) MEL requirements of Annex 6, Parts II and III.” The FAA does note, “However, some CAAs [civil aviation authorities] may not accept LOA D095 as a valid MEL approval.”

ICAO Annex 6 Part II spells out requirements for the operations of general aviation airplanes and is roughly equivalent to Part 91 of the federal aviation regulations. It states operators must have an “MEL approved by the State of Registry of the aeroplane,” which has been established “based on the relevant master minimum equipment list (MMEL).”

D095 LOAs state clearly that the “LOA and the MMEL with the procedures document…must be carried on board the aircraft as prescribed by Section 91.213 (a)(2) and are considered the approved MEL.” The “procedures document” is a mandatory, yet often not well understood, leg on which the tripod of the MEL stands. Most turbine pilots are familiar with their aircraft’s MMEL and dutifully carry their D095 LOA, yet a sizeable number are not conversant with the requirement to carry, nor the contents of, the procedures document.

There are eight items the FAA says must be included in the procedures document, however most of the document will consist of operations and maintenance (O and M) procedures corresponding to those listed in the MMEL. It was specifically either failure to develop and carry proper O and M procedures, or lack of crew familiarity with the location and use of said procedures, that was the proximate reason for the controversy surrounding D095 LOAs blowing up several years ago.

Consider the pilot of an Embraer Phenom 100 faced with inoperative automatic pressurization control. The MMEL spells out a list of operational procedures that must be complied with if the aircraft is to be flown using manual pressurization control (previous page). While some required no expanded explanation e.g. “airplane is operated with a crew of two,” “airplane is operated at or below FL 250”, the specifics of how to comply with steps b) through e) are more complex and must be listed in the procedures document. Just verifying the “auto control channel cabin pressurization indications on EIS” (step d) requires four steps (above). If, during a European ramp inspection, a pilot was asked how to MEL the auto pressurization control and did not reference a comprehensive O and M document, they would be issued a “finding” (violation), for operating without a valid MEL.

Another mandatory, yet easily overlooked, step in creating a compliant procedures document is enunciated in abstruse verbiage contained in D095 LOAs: “The operator must also list the ‘as required by FAR’ by specific part and section of the applicable regulations or state the operational requirements/limitations for dispatch.”

More simply put, whenever an MMEL item references the FARs as a condition of deferring inoperative equipment, the procedures document must either provide the specific FAR with part and section (in which case the operator must carry current FARs on board the aircraft), or they can spell out what the implication of the relevant FAR(s) would be, in specific detail relating to the deferred item in question.

For example, the Gulfstream GVII (G500/G600) MMEL says the following about deferring one or more inoperative VHF com radios: “Any in excess of those required by 14 CFR may be inoperative provided it is not powered by the Emergency AC Bus, Emergency DC Bus, Battery Bus, Battery Direct Bus, or the DC Transfer Bus and not required for emergency procedures.”

An approved MEL for the same airplane distills that verbose passage into a note that Com 1 must be operative, as it is powered by the Emergency Bus, then presents two choices:Option 1: “Number 2 or 3 may be inoperative.”

Option 2: “Number 2 and 3 may be inoperative provided overwater operations in excess of 30 minutes flying time or 100 nautical miles from the nearest shore are not conducted.”

Rather than referencing FAR 91.511a (which spells out the requirements for radio communication equipment when conducting overwater operations), the MEL translates the regulation into clear language.

Fortunately for small flight departments and owner operators with limited resources, it is not necessary for the operator to create their own procedures document in house. Due to the complexity of submitting an LOA application with all supporting material to the FAA, most operators use a third-party service to facilitate the application. These same services will typically provide a compliant procedures document with all the mandatory elements to the operator. The operator’s sole, but critical, responsibility is to ensure the document is carried on the aircraft with the LOA and MMEL, and most importantly, to ensure all pilots who operate the aircraft are familiar with its contents and use.

Neil Singer is a corporate pilot, designated pilot examiner, and instructor in Embraer Phenoms and Cessna Citations. He has more than 10,000 hours of flight time.