Airworthiness: ACS Task B in Full

Airworthy is a legal term with two parts. Section 3.5(a): "Airworthy means the aircraft conforms to its type design and is in a condition for safe operation" 1. Both parts must be true. The airplane must match the design the FAA approved, and it must be in a condition for safe operation. An airplane that fails either part is not airworthy.

The conformity part

An airplane with an unapproved part installed is unairworthy, even if everything works. The conformity part fails. Each of these takes the airplane outside its type design:

• a carburetor that the FAA never approved for the engine
• a propeller from a different type certificate
• an avionics installation with no approved data.

Each gauge can read normally and the airplane is still not airworthy under section 3.5 1.

The condition part

An unmodified airplane with a cracked spar is unairworthy. The condition part fails. The airplane matches its type design, and it is not in a condition for safe operation 1. The two parts are independent, and the pilot checks both. The records answer the conformity question. The walkaround and the run-up answer the condition question.

Statements about airworthiness

A fraudulent statement about airworthiness in a sales record is itself a violation. Section 3.5(b), for information "related to an advertisement or sales transaction," prohibits "Any fraudulent or intentionally false statement in any record about the airworthiness of a type-certificated product, or the acceptability of any product, part, appliance, or material for installation on a type-certificated product" 2. A logbook entry that records an inspection no one performed, shown to a buyer, is a separate offense from the missing inspection.

The owner or operator is primarily responsible for keeping the airplane airworthy. Section 91.403(a): "The owner or operator of an aircraft is primarily responsible for maintaining that aircraft in an airworthy condition, including compliance with part 39 of this chapter" 3. Part 39 is the airworthiness directives. Section 91.403(a) names part 39 inside the owner's responsibility.

The pilot in command

The pilot in command is responsible for deciding whether the airplane is in condition for safe flight. Section 91.7(b): "The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur" 4. The owner's responsibility is maintenance. The pilot's responsibility is the decision before and during each flight. The two overlap on each flight, and neither transfers to the other.

Owner or operator

The rule says owner or operator. A renter operating the airplane shares legal exposure for a lapsed inspection 5. AC 39-7D defines operate for the directives: "to “operate” not only means piloting the aircraft, but also causing or authorizing the product to be used for the purpose of air navigation, with or without the right of legal control as owner, lessee, or otherwise" 5. The student who rents the Warrior is an operator when the student flies it. The school's maintenance records are therefore the student's concern.

What the owner must do

Section 91.405 lists the owner's duties. Each owner or operator "Shall have that aircraft inspected as prescribed in subpart E of this part and shall between required inspections, except as provided in paragraph (c) of this section, have discrepancies repaired as prescribed in part 43 of this chapter" 6. The owner must have discrepancies repaired between inspections, not saved for the next annual. The owner also "Shall ensure that maintenance personnel make appropriate entries in the aircraft maintenance records indicating the aircraft has been approved for return to service" 6. The mechanic writes the entry. The owner is responsible for the entry existing.

After any maintenance, the airplane needs two things before anyone operates it. Section 91.407(a): "No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless— (1) It has been approved for return to service by a person authorized under § 43.7 of this chapter; and (2) The maintenance record entry required by § 43.9 or § 43.11, as applicable, of this chapter has been made" 7. The approval and the entry are separate conditions. An airplane with the work done and no entry is not legal to fly.

What the signature means

The mechanic's signature approves return to service only for the work performed. Section 43.9(a)(4): "The signature constitutes the approval for return to service only for the work performed" 8. A signature under an oil change says the mechanic did the oil change satisfactorily. It says nothing about the magnetos, the annual, or the directives. A pilot who takes returned to service as a statement about the whole airplane reads more than the signature says.

The check flight

Some maintenance requires a check flight before passengers ride. Section 91.407(b): "No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records" 9. The minimum qualification for that flight is a private pilot certificate. The pilot logs the flight in the airplane's records, not only in the pilot's logbook.

Ground tests can replace the check flight. Section 91.407(c): "The aircraft does not have to be flown as required by paragraph (b) of this section if, prior to flight, ground tests, inspection, or both show conclusively that the maintenance, preventive maintenance, rebuilding, or alteration has not appreciably changed the flight characteristics or substantially affected the flight operation of the aircraft" 9. Conclusively is the standard. A rigging change after control surfaces come off is a common case where no ground test is conclusive.

The first flight after the shop

North Aero treats the first flight after maintenance as the highest-paperwork-risk flight of the airplane's year. Before accepting the airplane, the pilot reads the return-to-service entry for the work performed 7. The entry says three things:

• what the mechanic opened
• what the mechanic replaced
• who signed.

The walkaround then starts at the places the entry names:

• the cowling that came off
• the control surface the shop repainted
• the fuel line the shop replaced.

In North Aero's experience, primary training rarely considers the risk of taking an airplane out of maintenance. North Aero considers it on each post-maintenance dispatch.

The flight of N13LV

On June 25, 2023, at 4:20 in the afternoon, a Mooney M20R lost engine power on the initial climb. The departure airport was Cape Fear Regional Jetport at Oak Island, North Carolina, bound for Southport. The airplane came down in a residential area half a mile short of the runway. The pilot, a 69-year-old instrument-rated private pilot who had reported 3,945 hours on his last medical application, died 10.

The airplane went into the shop in October 2022 and stayed eight months. "The private pilot/owner had requested that the mechanic troubleshoot interior lighting, service the brakes, attach a standby vacuum hose, and repair an exhaust leak. The mechanic could not complete the work as he could not start and run up the engine due to dead batteries" 10. The batteries were the first finding. "Specifically, the airplane was designed with a 24-volt electrical system that utilized two 24-volt batteries; however, the mechanic found four 12-volt batteries installed. When the mechanic contacted the pilot about the discrepancy, the pilot instructed him to reinstall the four 12-volt batteries. The mechanic refused, as it would have been an unapproved and unairworthy installation. The pilot then stated that he wanted his airplane back. The mechanic told him that the airplane was unairworthy, as he had not completed repairs on it; he also noted that it was unairworthy on the invoice" 10.

The airplane's logbooks were never recovered. The pilot told the mechanic that the last annual was completed in Pennsylvania in August 2022 10. On the day of the accident, "witnesses at the airport observed excessive white exhaust smoke and oil leaking from the airplane onto the ground as it taxied from the mechanic's hangar to runway 23 for takeoff. Shortly after takeoff, the pilot reported an engine failure on the common traffic advisory frequency and that he was returning to runway 23" 10. The airplane flew a left circuit and came down in a residential yard half a mile short of the threshold.

The engine examination showed the cause. "An oil sump accessory port plug was observed loose, with oily blue stained baffling material resting below it. Additionally, the No. 4 connecting rod had protruded through the top of the engine case. A check of the oil dipstick revealed no measurable oil in the engine. The engine likely failed due to oil starvation as the oil leaked from a loose oil sump accessory port plug as a result of uncompleted maintenance work" 10. The probable cause: "The pilot's improper decision to fly a known unairworthy airplane, which resulted in a total loss of engine power due to oil starvation" 10.

Where the pilot could have prevented the accident

An owner took his airplane out of an open maintenance job, over the mechanic's written note that it was unairworthy, and flew it. Each decision below carries the PAVE category that applied to it.

A calendar-month interval runs to the last day of the month. Section 91.409(a) requires the annual "within the preceding 12 calendar months" 11. An annual signed on March 10 is valid through March 31 of the next year, not through March 10. The same arithmetic applies to the 24-calendar-month transponder and altimeter checks and to the medical certificate.

The 100-hour

The 100-hour inspection applies in only two cases. Section 91.409(b): "no person may operate an aircraft carrying any person (other than a crewmember) for hire, and no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection" 11. A school airplane used for instruction for hire needs it. A private owner flying friends for free does not.

An annual can substitute for a 100-hour, because the rule says "an annual or 100-hour inspection" 11. A 100-hour never substitutes for an annual. Section 91.409(a): "No inspection performed under paragraph (b) of this section may be substituted for any inspection required by this paragraph unless it is performed by a person authorized to perform annual inspections and is entered as an “annual” inspection in the required maintenance records" 11.

Same scope, different signature

The annual and the 100-hour have the same scope. Both follow appendix D of part 43 12, and section 43.15 requires a checklist that includes "the scope and detail of the items contained in appendix D" for each 13. The difference is who can sign. A mechanic holding an inspection authorization must sign an annual. Section 65.95(a) gives the holder of an inspection authorization the privilege to "Perform an annual, or perform or supervise a progressive inspection" 14. An airframe and powerplant mechanic without the authorization can sign a 100-hour, and cannot sign an annual.

The ten hours

The airplane can exceed the 100-hour limit by up to 10 hours, and only to reach a place where the inspection can be done. Section 91.409(b): "The 100-hour limitation may be exceeded by not more than 10 hours while en route to reach a place where the inspection can be done" 11. The overflight time counts toward the next interval: "The excess time used to reach a place where the inspection can be done must be included in computing the next 100 hours of time in service" 11. An airplane inspected at 106 hours is due again at 200, not 206.

An annual that finds the airplane unairworthy ends with a list, not a permanently grounded airplane. Section 43.11(a)(5) gives the entry: "I certify that this aircraft has been inspected in accordance with (insert type) inspection and a list of discrepancies and unairworthy items dated (date) has been provided for the aircraft owner or operator" 15. The inspector "must give the owner or lessee a signed and dated list of those discrepancies" 15. The owner then repairs the items, or obtains a special flight permit to a place where repair can be done.

Progressive inspection

A progressive inspection program can replace the annual and 100-hour cycle. Section 91.409(d): "Each registered owner or operator of an aircraft desiring to use a progressive inspection program must submit a written request to the responsible Flight Standards office," and the program "shall provide for the complete inspection of the aircraft within each 12 calendar months" 16. The program still inspects the whole airplane each year, in pieces spread across the year.

The exceptions

Four kinds of certificate put an airplane outside the annual and 100-hour rules. Section 91.409(c): paragraphs (a) and (b) do not apply to "An aircraft that carries a special flight permit, a current experimental airworthiness certificate, a special airworthiness certificate in the light-sport category, or provisional airworthiness certificate" 17. An experimental airplane has a condition inspection in its operating limitations instead. A ferry permit airplane flies under the permit's own conditions.

Maintenance records come in two kinds. Section 91.417(a)(1) names "Records of the maintenance, preventive maintenance, and alteration and records of the 100-hour, annual, progressive, and other required or approved inspections" 18. Section 91.417(a)(2) names the permanent status records:

• "The total time in service of the airframe, each engine, each propeller, and each rotor"
• "The current status of life-limited parts"
• "The time since last overhaul of all items installed on the aircraft which are required to be overhauled on a specified time basis"
• "The current inspection status of the aircraft"
• "The current status of applicable airworthiness directives (AD) including, for each, the method of compliance, the AD number and revision date. If the AD involves recurring action, the time and date when the next action is required"
• copies of the Form 337s for each major alteration 18.

How long

The owner keeps work and inspection records until the work is repeated or superseded, or for one year. Section 91.417(b)(1): the (a)(1) records "shall be retained until the work is repeated or superseded by other work or for 1 year after the work is performed" 19. The status records stay with the airplane. Section 91.417(b)(2): they "shall be retained and transferred with the aircraft at the time the aircraft is sold" 19. The AD status record must show three things for each directive:

• the method of compliance
• the AD number and revision date
• the next due time, if the AD recurs 18.

Who can see them

The owner must make maintenance records available on request. Section 91.417(c): "The owner or operator shall make all maintenance records required to be kept by this section available for inspection by the Administrator or any authorized representative of the National Transportation Safety Board (NTSB)" 19.

What an entry contains

A maintenance record entry has four parts. Section 43.9(a):

• "A description (or reference to data acceptable to the Administrator) of work performed"
• "The date of completion of the work performed"
• the name of the person who did the work, if different from the signer
• "the signature, certificate number, and kind of certificate held by the person approving the work" 8.

Major repairs and major alterations get one more document. Section 43.9(d): "major repairs and major alterations shall be entered on a form, and the form disposed of, in the manner prescribed in appendix B, by the person performing the work" 20. The form is FAA Form 337. Plane Sense: "A mechanic who performs a major repair or major alteration shall record the work on FAA Form 337 and have the work inspected and approved by a mechanic who holds an inspection authorization (IA)" 21.

The records decide

Deciding an airplane is legal to fly requires reading its maintenance records. The cockpit documents alone cannot prove it. The airworthiness certificate has no expiration date, and the registration says nothing about the annual. Five items are in the records:

• the annual
• the 100-hour
• the AD status
• the ELT battery
• the transponder check 11.

The North Aero dispatch binder carries the record summary for each airplane, and the student reads it before the first flight of the day.

The ELT battery has two replacement triggers. Section 91.207(c): batteries "must be replaced (or recharged, if the batteries are rechargeable)— (1) When the transmitter has been in use for more than 1 cumulative hour; or (2) When 50 percent of their useful life (or, for rechargeable batteries, 50 percent of their useful life of charge) has expired" 22. The person who replaces the battery marks the new date on the transmitter and enters it in the records.

The transponder check

The transponder check each 24 calendar months applies to VFR airplanes too. Section 91.413(a): "No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or § 135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested and inspected" 23. Each use of the transponder requires a current check. A VFR Warrior in Class C airspace needs it.

The altimeter check

The 24-calendar-month altimeter and static system check is an IFR requirement. Section 91.411(a) applies to flight "in controlled airspace under IFR" 24. A VFR-only airplane does not need it. A school airplane that flies instrument training under IFR does.

An airworthiness directive is a regulation. Section 39.7: "Anyone who operates a product that does not meet the requirements of an applicable airworthiness directive is in violation of this section" 25. AC 39-7D: "ADs are regulations issued under part 39. Therefore, no person may operate a product to which an AD applies, except in accordance with the requirements of that AD" 5. Operate includes "causing or authorizing the product to be used for the purpose of air navigation" 5. The owner who authorizes the flight and the renter who flies it both violate section 39.7.

When compliance is due

Each AD sets its own compliance time, and an inspection date does not change it. AC 39-7D: "The belief that AD compliance is only required at the time of a required inspection (e.g., at a 100-hour or annual inspection) is not correct. The required compliance time is specified in each AD, and no person may operate the affected product after expiration of that stated compliance time" 26. An FAA-approved alternative method of compliance can change the time 26. An airplane can be current on its inspections and out of compliance with an AD at the same time. The 10-hour inspection overflight of 91.409(b) never extends an AD compliance time, because the AD sets its own time 26.

One time or recurring

ADs are one-time or recurring. AC 39-7D: "Some ADs require repetitive or periodic inspection" 27. A recurring AD repeats at stated intervals of hours or calendar time, and the record must show when the next action is due 18.

Applicability

When an AD lists no serial numbers, it applies to each serial number. AC 39-7D: "Limitations may be placed on applicability by specifying the serial number or number series to which the AD is applicable. When there is no reference to serial numbers, all serial numbers are affected" 28. An AD that a serial number or part number rules out still gets a recorded determination that it does not apply. That entry shows the directive was checked against this airplane, beside the status record section 91.417(a)(2)(v) requires for each applicable directive 18.

The inspector's duty

Each annual and 100-hour inspector must determine AD compliance. Section 43.15(a) requires the inspector to "Perform the inspection so as to determine whether the aircraft, or portion(s) thereof under inspection, meets all applicable airworthiness requirements" 13. AC 39-7D says the same: "§ 43.15(a) requires the person performing the inspection to determine that all applicable airworthiness requirements are met, including compliance with ADs" 27. The owner remains primarily responsible: "The owner or operator of an aircraft is primarily responsible for maintaining that aircraft in an Airworthy condition, including compliance with ADs" 27.

A manufacturer's service bulletin is not binding under part 91 by itself, even when stamped MANDATORY. Part 39 binds. A manufacturer's document does not, unless a regulation adopts it. Section 91.403(c) is one rule in part 91 that adopts a manufacturer's document: "No person may operate an aircraft for which a manufacturer's maintenance manual or instructions for continued airworthiness has been issued that contains an airworthiness limitations section unless the mandatory replacement times, inspection intervals, and related procedures specified in that section ... have been complied with" 29. A service bulletin becomes compulsory through an AD that adopts it or through an airworthiness limitations section. Otherwise it is advice.

SAIBs

A Special Airworthiness Information Bulletin is information, never a requirement. FAA Order 8110.100B: an SAIB "contains non-regulatory, non-mandatory information and guidance for safety issues that do not meet the criteria for airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39" 30. The FAA uses it "to alert, educate, and make recommendations" 30. The three documents differ in force:

• the AD is law
• the service bulletin is the manufacturer's advice
• the SAIB is the FAA's advice.

A special flight permit lets an unairworthy airplane that is capable of safe flight fly to a repair base. Section 21.197(a): "A special flight permit may be issued for an aircraft that may not currently meet applicable airworthiness requirements but is capable of safe flight, for the following purposes: (1) Flying the aircraft to a base where repairs, alterations, or maintenance are to be performed, or to a point of storage" 31. The other purposes in the rule are:

• "Delivering or exporting the aircraft"
• "Production flight testing new production aircraft"
• "Evacuating aircraft from areas of impending danger"
• "Conducting customer demonstration flights in new production aircraft that have satisfactorily completed production flight tests" 31.

The forms

The application is FAA Form 8130-6, and the permit is Form 8130-7. Plane Sense: "A special flight permit is an FAA Form 8130-7, Special Airworthiness Certificate, issued pursuant to 14 CFR part 21, section 21.197, for an aircraft that may not currently meet applicable airworthiness requirements but is safe for a specific flight," and "An applicant for a special flight permit must submit FAA Form 8130-6, Application for U.S. Airworthiness Certificate" 32. A ferry permit is itself a special airworthiness certificate. Section 21.175(b) lists "Aircraft operating under a special flight permit" among the special airworthiness certificates 33.

What the permit does not do

A special flight permit never authorizes a deviation from part 91. Plane Sense: "A special flight permit is not an authorization to deviate from the requirements of 14 CFR part 91" 32. Each of these still applies:

• the fuel reserve
• the minimum altitudes
• the VFR minimums.

The permit changes the airworthiness question, not the operating rules.

The AD that grounds you away from home

When an AD grounds an airplane away from a repair base, a permit is the legal way to the base if the AD allows it. AC 39-7D: "In some instances, you may need to fly an aircraft to a repair facility to do the work required by an AD. Unless the AD states otherwise, you may apply to the FAA for a special flight permit following the procedures in part 21, § 21.199" 26. Plane Sense gives the other case: "If an Airworthiness Directive (AD) requires compliance before further flight and does not have a provision for issuance of a special flight permit, the operation of the aircraft to which it applies would not be appropriate, and a special flight permit will not be issued" 32.

A private pilot can perform preventive maintenance on an airplane the pilot owns or operates. Section 43.3(g): "the holder of a pilot certificate issued under part 61 may perform preventive maintenance on any aircraft owned or operated by that pilot which is not used under part 121, 129, or 135 of this chapter" 34. The privilege needs at least a private or sport pilot certificate. AC 43-12A: "Section 43.7 limits the privilege to persons holding at least a private or sport pilot certificate" 35.

The list is the definition

The preventive maintenance list in part 43 appendix A is exclusive. If a task is not on the list, it is not preventive maintenance. AC 43-12A: "If a task or maintenance function does not appear in the list, it is not preventive maintenance" 36. The list includes:

• "Removal, installation, and repair of landing gear tires"
• "Replacing safety belts"
• "Replacing bulbs, reflectors, and lenses of position and landing lights"
• "Replacing or cleaning spark plugs and setting of spark plug gap clearance"
• "Replacing prefabricated fuel lines"
• "Cleaning or replacing fuel and oil strainers or filter elements"
• "Replacing and servicing batteries" 37.

Complex assembly

Even a listed task stops being preventive maintenance when it involves complex assembly operations. The opening sentence of appendix A(c): "Preventive maintenance is limited to the following work, provided it does not involve complex assembly operations" 37. AC 43-12A: "because of differences in aircraft, a function may be preventive maintenance on one aircraft and not on another" 36. A tire change on a Warrior is preventive maintenance. A tire change that requires disassembly of a retractable gear is not always preventive maintenance.

Logging it

The pilot must log preventive maintenance the same way a mechanic logs work. Section 43.9(a) requires the description, the date, and "the signature, certificate number, and kind of certificate held by the person approving the work" 8. The pilot's signature returns to service only the pilot's own work: "pilots may only approve for return to service preventive maintenance which they themselves have accomplished" 35. Section 91.407(a) still applies to pilot-performed preventive maintenance. AC 43-12A: "§ 91.407(a)(1) prohibits operation of the aircraft unless approved for return to service" 35. The entry exists before the next flight, or the next flight is illegal.

When the pilot finds equipment inoperative, the governing rule is 91.213. Section 91.205 is one screen inside the second path of 91.213, not the first question. The question is not whether the item is on the 91.205 list. The question is which path of 91.213 applies. There are three paths. AC 91-67A: "Section 91.213 provides three methods for operating an aircraft with inoperative instruments or equipment installed. The relief could be obtained: Through an MEL and LOA; Under the provisions of § 91.213(d); or Under a special flight permit (SFP) issued in accordance with §§ 21.197 and 21.199" 38.

No application

Using 91.213(d) needs no application or approval. AC 91-67A: "No application, written request, or approval is required to operate under § 91.213(d)" 39. The pilot and the mechanic work the process on the ramp, with the records.

Step zero: is there an MEL

Step zero is confirming whether the operator holds an MEL and a letter of authorization. Section 91.213(a) requires, for the MEL path, that "An approved Minimum Equipment List exists for that aircraft" and "The aircraft has within it a letter of authorization, issued by the responsible Flight Standards office, authorizing operation of the aircraft under the Minimum Equipment List" 40. If an approved MEL exists, the 91.213(d) process does not apply, and the MEL governs. The MEL and its letter are a supplemental type certificate: "The Minimum Equipment List and the letter of authorization constitute a supplemental type certificate for the aircraft" 40. North Aero's Warriors have no MEL, so the answer at step zero is no and the (d) process applies.

What an MEL cannot include

Three classes of item can never be on an MEL. Section 91.213(b):

• "Instruments and equipment that are either specifically or otherwise required by the airworthiness requirements under which the aircraft is type certificated and which are essential for safe operations under all operating conditions"
• "Instruments and equipment required by an airworthiness directive to be in operable condition unless the airworthiness directive provides otherwise"
• "Instruments and equipment required for specific operations by this part" 40.

Turbines

A turbine-powered airplane cannot use 91.213(d). Section 91.213(d)(1) allows the path only in a "non-turbine-powered airplane" 41. AC 91-67A lists the excluded types: "Certain aircraft may not be operated under § 91.213(d), including: Turbine-powered airplanes" 39. A turbine airplane with a broken item needs an MEL or a permit.

Section 91.213(d)(2) has four screens, and an item must pass all four. The first: the item must not be "Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated" 41. Answering the first screen is research, not recall. The pilot answers it in three steps:

• find the type certificate data sheet
• read the certification basis
• read that rule's equipment requirements.

Section 21.41 makes the data sheet part of the certificate: "Each type certificate is considered to include the type design, the operating limitations, the certificate data sheet, the applicable regulations of this subchapter with which the FAA records compliance" 42.

The Warrior is the worked example. Data sheet 2A13, for the "PA-28-140 and PA-28-151: CAR 3 effective May 15, 1956, including Amendments 3-1, 3-2, and 3-4" 43. The Warrior's certification basis begins with Civil Air Regulations part 3 of 1956, with a few named part 23 sections added later. A pilot who answers screen one from part 23 alone has read the wrong rule.

Screen two: the equipment list and the KOEL

The second screen: the item must not be "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" 41. A KOEL lists the equipment required for each kind of operation: day VFR, night VFR, IFR. Many light airplanes have none. The Warrior's manual has an equipment list and no KOEL.

When the equipment list marks nothing required and there is no KOEL, North Aero applies a conservative default: each factory-installed item counts as required. The rule leaves the question open, and the school answers it with the stricter reading. The school treats a broken factory item as a broken required item until the mechanic and the records show otherwise.

Screens three and four

The third screen: the item must not be "Required by § 91.205 or any other rule of this part for the specific kind of flight operation being conducted" 41. Section 91.205 applies here, as one screen among four, for the kind of flight planned. A landing light passes screen three for a private day flight and fails it for a night flight for hire. The fourth screen: the item must not be "Required to be operational by an airworthiness directive" 41. An AD that requires an item operative closes the (d) path for that item.

An item that passes the four screens then needs removal or deactivation, and a placard. Section 91.213(d)(3): the item is "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" 41.

Deactivation is maintenance

Deactivation is not preventive maintenance. AC 91-67A: "Deactivation of an inoperative system is not preventive maintenance as described in part 43 appendix A. Regardless of the method of deactivation, a person authorized to approve the aircraft for return to service under § 43.7 must make the maintenance record entry required by § 43.9" 44. Switching an item off is not deactivating it: "Deactivation may involve more than simply turning off a system switch, which does not remove power from the system. Deactivation may involve pulling and securing the circuit breaker and/or removing the equipment" 44. The pilot does not deactivate a system on the ramp with a switch and a piece of tape.

The determination

The final step is a determination by a certificated pilot or a mechanic. Section 91.213(d)(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" 41. An airplane handled correctly under (d) is legal: "An aircraft with inoperative instruments or equipment as provided in paragraph (d) of this section is considered to be in a properly altered condition acceptable to the Administrator" 41.

Until the next inspection

Items deferred under (d) do not stay deferred. Section 91.405(c): the owner "Shall have any inoperative instrument or item of equipment, permitted to be inoperative by § 91.213(d)(2) of this part, repaired, replaced, removed, or inspected at the next required inspection" 6. The placard lasts only until the next annual or 100-hour.

Legal and safe

Legal is not the same as safe. After the 91.213 paperwork, the pilot's hazard judgment under (d)(4) and 91.7(b) still decides the flight 41. Section 91.7(b) makes the pilot in command responsible for deciding whether the airplane "is in condition for safe flight" 4. An inoperative item can pass all four screens and carry a correct placard. It can still be a hazard for this flight in this weather at this airport. The pilot makes the determination for the flight, not for the airplane in general.

The operator must display the airworthiness certificate where a passenger or crewmember can read it. Section 91.203(b): "No person may operate a civil aircraft unless the airworthiness certificate required by paragraph (a) of this section or a special flight authorization issued under § 91.715 is displayed at the cabin or cockpit entrance so that it is legible to passengers or crew" 45.

The blank expiration date

A standard airworthiness certificate has no expiration date, and its validity is conditional. Section 21.181(a)(1): standard certificates "are effective as long as the maintenance, preventive maintenance, and alterations are performed in accordance with parts 43 and 91 of this chapter" 46. An airplane whose annual has lapsed still carries the certificate in the pocket, and the certificate is not in effect. The blank date means conditional, not unlimited.

Registration

An airplane's registration certificate expires seven years after the last day of the month of issue. Section 47.40(a): "A Certificate of Aircraft Registration issued in accordance with § 47.31 expires seven years after the last day of the month in which it is issued" 47. Older materials say three years. That answer is out of date, and the examiner knows the current rule.

Experimental

An experimental airworthiness certificate carries operating limitations. Section 91.319 restricts an experimental airplane. Its paragraph (a) bars carrying persons or property for compensation or hire in the operations it names 48. The FAA issues the limitations with the certificate, and they are part of it. A student who is offered a ride in an experimental airplane reads the limitations before agreeing to pay for fuel.