AC 121-1A

Change 4Historical

Advisory circular · Standard Operations Specifications - Aircraft Maintenance Handbook

Approved
July 7, 1978
Last reviewed
October 25, 2024
Cancels
AC121-1A CHG 3AC120-21AC120-24A
Family
AC 121-1 · 1 version
Revision
A, change 4
14 CFR parts
1

Guidance, not mandatory unless a rule or AD requires it. DRS record last changed November 22, 2025.

Show pages 358–369
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HR - Indicates "Hours" MO - indicates "Months" YRS - Indicates "Years" Effective date ____________________ Page 1 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36 Maintenance and inspections shall be accomplished in accordance with the applicable procedures as listed in ABC Airlines Maintenance Manual.

#1 insp. shall be accomplished prior to the originating flight from a maintenance base each day. In the event the aircraft is away from a station where qualified maintenance personnel are not available, the #1 inspection shall be accomplished prior to exceeding 20 hours time in service or seven days, whichever comes first.

#2 insp. shall be accomplished at basic intervals of 75 hours times in service and shall be repeated each 75 hours time in service after a #3 or #4 inspection has been accomplished.

#3 insp. shall be accomplished at intervals not to exceed 150 hours time in service.

#4 insp. shall be accomplished at intervals not to exceed 300 hours time in service.

Te inspection cycle #2, #3, #2, #4, #2, #3, etc., shall be repeated in this sequence.

In addition to the #1, #2, #3, #4 inspections there are (other) inspections required. These inspections are explained in the notes below or are self-explanatory.

Overhaul times listed in hours, years and cycles are maximum limits, whichever comes first. Time replacement items must be replaced where "replace" is indicated.

ESV - Engine Shop Visit. The engine shop visit shall be accomplished at five hundred hours (500) time in service in accordance with Airesearch TFE 731-72 maintenance manual.

NOTE 1: Replace engine elements having service life limits as

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established in Airesearch Service Bulletin TFE 731-72-3001, Revision #4, dated 2-28-75 and AD 75-05-12 pertaining to Airesearch Manufacturing Company.

NOTE 2: Replace structural components at replacement lives shown in FAA approved Learjet Report 26-S47. These replacement lives are also shown in the Learjet Model 35 Maintenance Manual (ref. Type Data Sheet No. ATOCE under "Equipment").

Effective date _______________________ Page 2 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 21 - Air Conditioning Air Conditioning System OC X Valve, Bleed Air Check 6,000 10 X Valve, Flow Control 4,000 4 X Valve, Hot Air Bypass 6,000 10 X Heat Exchanger 6,000 10 X Valve, Ram Air Check 6,000 10 X Indicator, Temp Control 6,000 10 X Heater, Cabin Auxiliary 6,000 10 X Selector, Temperature 6,000 10 X Unit, Temperature Control OC X Sensor, Cabin Temperature OC X Thermostat, Hi Limit OC X Sensor, Duct Temperature OC X Sensor, Cabin Skin Temperature OC X Compressor, Freon 3,600 3 X X X Motor, Compressor 6,000 10 X X X Condensor 10,000 10 X Dehydrator 10,000 10 X Switch, Refrig. Pressure 6,000 10 X Evaporator 10,000 10 X Blower, Cabin 2,400 4 X Fan, Cockpit Cooling 2,400 4 X Valve, Expansion 6,000 8 X Valve, Cabin Air Exhaust 4,000 4 X Valve, Diff Press. Relief 6,000 10 X Pump, Pressurization Jet 6,000 10 X Module, Pressurization 6,000 10 FC @

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1200 hr Limiter, Cabin Altitude OC X Valve, Cabin Safety 4,000 4 X Aneroid, Cabin Press. Warning OC X FC @ 1200 hr Aneroid, Cabin Pressurization OC X FC @ 1200 hr Indicator, Cabin Temperature OC X Effective date _______________________ Page 3 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 22 - Auto Pilot Auto Pilot System OC X Controller, Autopilot OC X Computer/Controller, Yaw OC X Sensor, Air Data OC X Computer, Autopilot OC X BC @ 900 hr Accelerator, Lateral OC X Indicator, Yaw Damper OC X Capstan, Servos OC X SI @ 600 hr Actuator, Servo OC X SI @ 600 hr Computer, Mach Trim OC X Followup, Mach Trim OC X Rate Gyro OC X Box, Flt. Direct Interface OC X Chapter 23- Communications OC X X X X To be determined by assigned inspector.

Effective date _______________________ Page 4 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

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ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 24 - Electrical Power Electrical Power System OC X X X X Inverter, Primary OC X X X X Sensor, AC Overload OC X X X Relay, AC Power OC X X X Autotransformer OC X Inverter, Secondary OC X X X X Box, AC Parallel Control OC X Voltmeter, AC OC X X X X Generator OC X X X Regulator, Gen. Voltage OC X X X Sensor, Gen. Overload OC X Relay, Gen. Feeder Bus OC X Ammeter, Generator OC X X X Box, Generator Control OC X Voltmeter, DC OC X X X X Battery OC X X X X Relay, Battery OC X Switch, Batt. Hi Lim. Temp. OC X X X Sensor, Batt. Temp. OC X X X Indicator, Battery Temp. OC X X X X Battery, Emergency Light OC X X X X Receptacle, External Power OC X X X Relay, External Power OC X X X Chapter 25 - Equipment/ Furnishings Equipment & Furnishings OC X X X Seat, Crew OC X X X Seat, Passenger OC X X X Belt OC X X X Harness/Reel Shlder OC X X X Life Vests 24 mo. X X X Drag Chute OC X Effective date _______________________ Page 5 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

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OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 26 - Fire Protection Fire Protection System OC X X X X FC @ 600 hr Sphere, Fire Extinguisher 5 yrs. ** X X X X (ICC/DOT - 4DA) Cartridges, Explosive, Fire 3 yrs. X Exting.

Valve, Fire Ext. 2 Way Ck OC X X X FC @ 600 hr Element, Sensor OC X X X X Control Unit, Fire Detector OC X X X X Engine, Fire Detector System OC X X X X Extinguisher, Portable OC X X X (6BC Dry Chemical) ** Inspections, Hydrostatic Test, and Life Limits will be accomplished as set forth in Part 173, Chapter 1, Subtitle B of CFR 49 currently in effect.

Chapter 27 - Flight Controls Flight Controls OC X X X Aileron NOTE 2 X X X X SI @ 600 hr Drive Assy, Aileron NOTE 2 X X X Bolt, Ail. Drive Yoke NOTE 2 X X X Bolt, Ail. Hinge NOTE 2 X X X Tab, Aileron Trim NOTE 2 X X X X Actuator, Aileron Trim Tab OC X X X X FC @ 600 hr Potentiometer, Ail. Trim OC X X X FC @ 600 hr Tab, Aileron Balance NOTE 2 X X X X Wheel, Control 20,000 X X Column, Control 20,000 X X Cables, Flight Control NOTE 2 X X X Indicator, Ail. Trim Pos. OC X X X FC @ 600 hr Rudder NOTE 2 X X X SI @ 600 hr Hinges, Rudder NOTE 2 X X X Supports, Rudder NOTE 2 X X X Sector, Rudder Servo OC X X X Tab, Rudder NOTE 2 X X X X Actuator, Rudder Trim Tab OC X X X X FC @ 1200 hr Potentiometer, Rudder Trim OC X X X FC @

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1200 hr Indicator, Rudder Trim Pos. OC X X X X FC @ 1200 hr Effective date _______________________ Page 6 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 27 - continued Elevator NOTE 2 X X X SI @ 600 hr Downspring Assy, Elevator OC X X X SI @ 600 hr Stabilizer, Horizontal NOTE 2 X X X Hinge Pin, Horizontal NOTE 2 SI @ 600 Stabilizer hr Actuator, Horizontal OC SI @ 600 Stabilizer hr Bolt, Stabilizer Actuator NOTE 2 SI @ 600 Attach hr Indicator, Horizontal OC X X X X FC @ 600 Stabilizer Posi hr Flap Assembly NOTE 2 X X X X Actuator, Flap OC X X X Support, Flap NOTE 2 X Track, Flap NOTE 2 X Bushings, Flap Roller 1,200 X Valve, Flap Control OC X Bolts, Wing Flap Selector NOTE 2 X Restrictor, Flap OC X Valve, Flap Press, Relief OC X X X Indicator, Flap Position OC X X X X Potentiometer, Flap Position OC X X X Switch, Flap Airspeed OC X Spoiler, Assembly 3,600 X X X X Actuator Fitting & Bolts NOTE 2 X Spoiler Arm, Spoiler Actuator NOTE 2 X X X Brackets, Spoiler 2,400 X X X 1/4 Bolt, Spoiler Act Arm NOTE 2 X 5/16 Bolt, Spoiler Act Arm NOTE 2 X

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Switch, Spoiler Down/Lock OC X 1/4 Bolt, Spoiler Hinge NOTE 2 X 5/16 Bolt, Spoiler Hinge NOTE 2 X Switch, Spoiler Limit OC X X X Followup, Spoiler OC X X X Followup, Aileron Aug.-Ail. OC X X X Valve, Spoiler Servo OC X Valve, Spoiler Control OC X Valve, Spoiler Solenoid OC X Restrictor Computer Amp. Spoiler OC X X X Effective date ____________________ Page 7 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 27 - continued Filter, Spoiler 300 X Computer/Amp. Stall Warning OC X Transducer, Angle of Attack OC X X Bias Box, Stall Warning OC X Shaker, Control Column OC X X Accelerometer, Stall Warning OC X Indicator, Angle of Attack OC X Cutout, Stall Warning Acceler. OC X Chapter 28 - Fuel Fuel System OC X Pump, Jet OC X X X Valve, Tank Vent Ck. 10,000 10 X Valve, Tank Jettison 6,000 10 FC @600 hr Tank, Tip 20,000 X X X X Pump, Boost (Standby) 8,000 X X X X Switch, Wing Float 10,000 10 FC @ 600 hr Valve, Crossflow Shutoff 10,000 10 X X X X Valve, Fuselage Transfer 10,000 10 X X X X Shutoff Valve, Wing Press. Relief 10,000 10 X Valve, Wing Vacuum Relief 10,000 10 FC @ 600

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hr Cell, Fuselage Fuel 6,000 10 X X X Switch, Fuselage Tank Trans. 6,000 10 X X X Pres.

Switch, Fuselage Tank Float 10,000 10 X X X Valve, Fuel Shutoff 10,000 10 X X X X Valve, Motive Flow 10,000 10 X X X PC Board, Fuel Board 10,000 10 X C @ 600 hr Probe, Fuselage & Wing 10,000 10 X C @ 600 hr Indicator, Fuel Quantity 10,000 10 X C @ 600 hr Hoses, Engine Nacelle 2,400 X Hoses, Aircraft System 6,000 10 X Effective date ____________________ Page 8 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 29 - Hydraulic Power Hydraulic Power System OC X Reservoir, Hydraulic 20,000 X X X X Valve, Hydraulic Shutoff 6,000 10 X X X Pump, Engine Hydraulic EC X Accumulator, Hydraulic 10,000 10 X X X X Valve, Engine Hydraulic OC X X X Press. Ck.

Valve, Hydraulic Reserv. OC X X X Press. Relief Valve, Hydraulic System 6,000 10 X Relief Valve, Emergency Air OC FC @ 600 hr Indicator, Hydraulic Pressure OC X X X X Pump, Auxiliary Electric OC X X X X Regulator, Reservoir, Pressure OC X X X Hoses, Engine Nacelle 2,400 X Hoses, (all other except landing gear system) 6,000 X X X

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Chapter 30, Ice and Rain Protection Ice and Rain Protection OC X Regulator, Press. Anti-Ice OC X Thermostat, Wing Anti-Ice OC X Indicator, Temperature OC X Anti-Ice Valve, Nacelle Anti-Ice OC X Shutoff Valve, Defrost Pressure OC X Regulator Tank, Alcohol Anti-Ice OC X X X Pump, Motor Driven Anti-Ice OC X X X Filter, Alcohol Anti-Ice OC X Valve, Alcohol Pressure Relief OC X Pitot/Static System Heater OC X X X X Chapter 31 - Instruments Instruments System OC X X X X SI @ 600 hr Clock OC X X X X Unit, Aural Warning OC X X X Flight Recorder 2,000 X X X Effective date ____________________ Page 9 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 32 - Landing Gear Landing Gear System OC X X X X Strut, Main Gear Shock NOTE 2 X Actuator, Main Gear NOTE 2 X Valve, Shuttle Gear Actuator OC FC @ 600 hr Actuator, Door OC X Valve, Shuttle Gear Door OC X Arm, Main Gear Strut Torq. OC X Strut, Nose Gear NOTE 2 X X X Actuator, Nose Gear NOTE 2 X X X Valve, Nose Gear Priority OC X Valve, Shuttle, Nose Gear OC FC @ 600

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hr Actuator, Nose Gear Upltch. OC X Valve, Gear Selector OC X Valve, Gear Door Sequence OC X Valve, Emergency Air Shuttle OC FC @ 600 hr Bottle, Emergency Air (ICC/DOT) Type D-16 3 yrs.** X X X Indicator, Emergency Air OC X X X X Valve, Emergency Gear Extend OC FC @ 600 hr Valve, Emerency Brake OC FC @ 600 hr Wheel, Main Gear 2,500 X X X X Wheel, Nose OC X X X X Valve, Power Brake OC X X X Valve, Brake Shuttle OC FC @ 600 hr Brake OC X X X X Valve, Anti-Skid OC X FC @ 600 hr Control Box, Anti-Skid OC X FC @ 600 hr Computer/Amp, Nose Steer OC X Actuator, Nose Wheel Steer 3,000 X X X Servo, Nose Steering OC X Followup, Rudder Pedal OC X ** Inspections, Hydrostatic Test, and Life Limits will be accomplished as set forth in Part 173, Chapter 1, Subtitle B of CFR 49 currently in effect.

Effective date ____________________ Page 10 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 33 - Lights Light System OC X X X X Control Box, Warning Light OC X Light, Landing/Taxi OC X X X X Light, Strobe OC X X X X

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Power Sup. Strobe Light OC X X X Dim Assembly, Light OC X Transformer, Cold Cathode OC X Lights, Emergency (Interior OC X X X X and Exterior) Chapter 34 - Navigation OC X X X X To be determined by assigned inspector.

Effective date ____________________ Page 11 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 35 - Oxygen Oxygen System OC X NOTE 3 Detector, Flow OC X Cylinder, Pressure Oxygen X (ICC/DOT) 3AA 5 yrs.* Switch, Oxygen Aneroid OC X Valve, Lanyard Actuated OC X Mask, Oxygen OC X Indicator, Oxygen Pressure OC X X Valve, Manual Aneroid Bypass OC X Valve, Oxygen Solenoid OC X Valve, Manual Pass. Oxygen OC X * Inspections, Hydrostatic Test, and Life Limits will be accomplished as set forth in Part 173, Chapter 1, Subtitle B of CFR 49 currently in effect.

NOTE 3: Conduct a special functional check of the passenger oxygen system every 2,000 to 3,000 hours by simulating a cabin pressure of 14,000 to 15,000 feet altitude and checking the oxygen flow at each passenger mask.

Chapter 36 - Pneumatic Pneumatic System OC X Valve, Shutoff/Pressure Reg. OC X Thermoswitch, Pneumatic System OC X Chapter 52 - Doors

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Door, Cabin Assembly OC X X X Actuator, Cabin Door Lock OC X X X Door, Emergency OC X Chapter 53 - Fuselage Fuselage Fwd OC X X X X SI @ 600 hr Cabin OC X X X X SI @ 600 hr Cockpit OC X X X X SI @ 600 hr Tail Cone OC X X X X SI @ 600 hr Fuselage Aft OC X X X X SI @ 600 hr Chapter 54 - Nacelles/Pylons Nacelle/Pylon OC X X X X SI @ 600 hr Mount, Engine Fwd & Aft NOTE 2 X X X SI @ 600 hr Mount, Bolts NOTE 2 X X X SI @ 600 hr Effective date ____________________ Page 12 of 13

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE

ABC AIRLINES LEAR 35/36

OVERHAUL INSPECTION AND CHECK

HOURS OR PERIOD YEARS #1 #2 #3 #4 OTHER Chapter 55 - Stabilizers Empennage OC X X X X Hinge Assembly, Vertical NOTE 2 X X X SI @ 600 Stabil. hr Chapter 56 - Windows Windshield OC X X X X Window, Cabin OC X X X X SI @NOTE 4 Chapter 57 - Wings Wing OC X X X X SI @NOTE 4