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 48–59

Period Check Period Air Conditioning, Chapter 21 12,000 Blower, Nose Heater 6,000 Heater, Cabin 2,500 Heater, Nose 2,500 Auto-Pilot, Chapter 22 12,000 Electrical, Chapter 24 12,000 Ammeter & Voltmeter 6,000 Generator EC Inverter, Emergency 5,000 Inverter, Main 2,000 Regulator, Voltage 2,000 Relay, Battery 6,000 Equipment & Furnishings, Chapter 25 12,000 Chute, Evacuation 1 year First-Aid Kit 6 months Life Vest & Raft 1 year Transmitter, Emergency 6 months Fire Protection, Chapter 26 12,000 Cylinders * Panel, Fire Detector 6,000 Cylinder Weight Check 6 months * 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.

Flight Controls, Chapter 27 12,000 Indicator, Flap Position 6,000 Transmitter, Flap Position 6,000 Fuel, Chapter 28 12,000 Indicator, Fuel Quantity 5,000 Pump, Fuel Boost 4,500 Transmitter, Fuel Quantity 4,000 Hydraulic, Chapter 29 12,000 Accumulator 8,000 Indicator, Hydraulic Pressure 6,000 Pump, Auxiliary Hydraulic 6,000 Regulator, Pressure 6,000 Transmitter, Hydraulic Pressure 6,000 Firewall shutoff 5,000 Effective date _____________________

PAGE 2 of 2 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-4 Overhaul Inspection & Period Check Period Ice & Rain, Chapter 30 12,000 Indicator, Anti-ice Quantity 6,000 Indicator, Deice Pressure 6,000 Pump, Alcohol 8,000 Solenoids, Anti-ice 6,000 Transmitter, Anti-ice Quantity 6,000 Instruments, Chapter 31 12,000 Clock OC Landing Gear, Chapter 32 12,000 Bottle, Emergency Air * Wheels, Tires & Brakes OC Lights, Chapter 33 12,000 Flasher 4,000 Rotating Beacon OC Navigation, Chapter 34 12,000 Altimeter 3,000 ** Compass, Magnetic 6,000 Indicator, Air Speed 4,000 Indicator, Gyro Horizon 3,000 Indicator, Outside Air Temperature 6,000 Indicator, Rate of Climb 4,000 Indicator, Turn & Bank 3,000 ** Calibrate every 24 months Oxygen, Chapter 35 12,000 Bottle, Oxygen * * 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.

Fuselage, Chapter 53 12,000 Nacelles, Chapter 54 12,000 Stabilizers, Chapter 55 12,000

Wings, Chapter 57 12,000 Effective date _____________________ ---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 15. OPERATIONS SPECIFICATIONS AIRCRAFT MAINTENANCE

- DOUGLAS - DC-6, DC-7 Form Approved.

UNITED STATES OF AMERICA Budget Bureau FEDERAL AVIATION AGENCY No. 04-R075.

WASHINGTON PART D PAGE 1 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-6, DC-7 Overhaul Inspection & Period Check Period Air Conditioning, Chapter 21 12,000 Accessory Containers 4,000 Expansion Turbine 4,000 Actuators & Valves 6,000 Heater Unit 2,500 Turbo-Compressor 2,000 Unit, Ignition 2,500 Auto-Pilot, Chapter 22 12,000 Amplifier (A-12) 4,000 Engaging Control 8,000 Gyro-Compass Control 4,000 Gyro-Compass, Repeater 4,000 Pedestal Controller 6,000 Servo, Controller 2,500 Servo, Unit 6,000 Vertical Gyro Control 4,000 Electrical, Chapter 24 12,000 Ammeter & Voltmeter 6,000 Generator EC Inverter, Emergency 5,000 Inverter, Main 2,000 Regulator, Voltage 2,000 Relay, Battery 6,000 Equipment & Furnishings, Chapter 25 12,000 Chute, Evacuation 1 year

First-Aid Kit 6 months Life Vest & Raft 1 year Transmitter, Emergency 6 months Fire Protection, Chapter 26 12,000 Cylinders * Panel, Fire Detector 6,000 Cylinders, Weight Check 6 months * 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 2 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-6, DC-7 Overhaul Inspection & Period Check Period Flight Controls, Chapter 27 12,000 Indicator, Wing Flap Position 6,000 Transmitter, Wing Flap Position 6,000 Fuel, Chapter 28 12,000 Indicator, Fuel Quantity 4,500 Pump, Fuel Boost 4,500 Transmitter, Fuel Quantity 4,000 Hydraulic, Chapter 29 12,000 Accumulator 8,000 Indicator, Hydraulic Pressure 6,000 Pump, Auxiliary Hydraulic 6,000 Regulator, Pressure 6,000 Transmitter, Hydraulic Pressure 6,000 Ice & Rain Protection, Chapter 30 12,000 Accessory, Containers 4,000 Blowers, Wing & Empennage Heater 8,000 Heater, Wing & Empennage 8,000 Unit, Ignition 2,500 Instruments, Chapter 31 12,000 Clock OC Landing Gear, Chapter 32 12,000

Bottle, Emergency Air * Wheels, Tires & Brakes OC * Inspections, hydraulic test, and life limits will be accomplished as set forth in Part 173, Chapter 1, Subtitle B of CFR 49 currently in effect.

Lights, Chapter 33 12,000 Flasher 4,000 Navigation, Chapter 34 12,000 Altimeter 3,000 ** Compass, Magnetic 6,000 Indicator, Air Speed 4,000 Indicator, Gyro Horizon 3,000 Indicator, Outside Air Temperature 6,000 Indicator, Rate of Climb 4,000 Indicator, Turn & Bank 3,000 ** Calibrate every 24 months Effective date _____________________ PAGE 3 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-6, DC-7 Overhaul Inspection & Period Check Period Oxygen, Chapter 35 12,000 Cylinder * * 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.

Fuselage, Chapter 53 12000 Nacelles, Chapter 54 12000 Stabilizers, Chapter 55 12000 Wings, Chapter 57 12000 Effective date _____________________ ----------------------------------------------------------------

---------------------------------------------------------------- FIGURE 16. OPERATIONS SPECIFICATIONS AIRCRAFT MAINTENANCE

- LOCKHEED - L-049/749/1049/1649 Form Approved.

UNITED STATES OF AMERICA Budget Bureau FEDERAL AVIATION AGENCY No. 04-R075.

WASHINGTON PART D PAGE 1 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE LOCKHEED L-049/749/1049/1649 Overhaul Inspection & Period Check Period Air Conditioning, Chapter 21 12,000 Actuators & Valves 6,000 Blower, Flight Station 2,000 Expansion Turbine 4,000 Fan, Heat Exchanger Cooling 4,000 Heat Cycling & Overheat Assembly 9,000 Heater Unit 2,500 Ignition Unit 2,500 Indicator, Cabin Altitude 6,000 Indicator, Cabin Rate of Change 6,000 Pump, Cabin Supercharger Reactor 2,000 Pump, Heater Fuel 6,000 Selector, Cabin Altitude 6,000 Selector, Cabin Rate of Change 6,000 Separator, Water 6,000 Turbo-Compressor 2,000 Auto-Pilot, Chapter 22 12,000 Electrical, Chapter 24 12,000 Ammeter & Voltmeter 6,000 Generator EC Inverter, Emergency 5,000 Inverter, Main 2,000 Regulator, Voltage 2,000 Relay, Battery 6,000 Equipment & Furnishings, Chapter 25 12,000 Evacuation Chute OC First-Aid Kit 6 months Life Vests & Raft 6 months Transmitter, Emergency 4 months Fire Protection, Chapter 26 12,000

Cylinders * * Hydrostatic and life limits shall be entered here and shall not exceed those set forth in Part 173, Chapter I, Subtitle "B" of CFR Title 49.

Flight Controls, Chapter 27 12,000 Indicator, Wing Flap Position 6,000 Transmitter, Wing Flap Position 6,000 Effective date _____________________ PAGE 2 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE LOCKHEED L-049/749/1049/1649 Overhaul Inspection & Period Check Period Fuel, Chapter 28 12,000 Indicator, Fuel Quantity 4,000 Pump, Fuel Boost 4,000 Transmitter, Fuel Quantity 4,000 Hydraulic, Chapter 29 12,000 Accumulator 8,000 Dampener 8,000 Indicator, Hydraulic Pressure 6,000 Pump, Auxiliary Hydraulic 6,000 Regulator, Pressure 6,000 Ice & Rain, Chapter 30 12,000 Box, Windshield Anti-ice Control 4,000 Motor, Cowl Flap 4,000 Pump, Anti-ice 8,000 Pump, Deicer 4,000 Windshield Wiper Assembly 4,000 Instruments, Chapter 31 12,000 Clock OC Landing Gear, Chapter 32 12,000 Bottle, Emergency Air * Wheels, Tires & Brakes OC * Hydrostatic and life limits shall be entered here and shall not exceed those set forth in Part 173, Chapter I, Subtitle "B" of CFR Title 49.

Lights, Chapter 33 12,000

Flasher 4,000 Navigation, Chapter 34 12,000 Altimeter 3,000 ** Compass, Magnetic 6,000 Indicator, Air Speed 4,000 Indicator, Gyro Horizon 3,000 Indicator, Outside Air Temperature 6,000 Indicator, Rate of Climb 4,000 Indicator, Turn & Bank 3,000 ** Bench check every 12 months.

Effective date _____________________ PAGE 3 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE LOCKHEED L-049/749/1049/1649 Overhaul Inspection & Period Check Period Oxygen, Chapter 35 12,000 Bottle, Oxygen * Regulator, Oxygen Flow 8,000 Fuselage, Chapter 53 12,000 Nacelles, Chapter 54 12,000 Stabilizers, Chapter 55 12,000 Wings, Chapter 57 12,000 * Hydrostatic and life limits shall be entered here and shall not exceed those set forth in Part 173, Chapter I, Subtitle "B" of CFR Title 49.

Effective date _____________________ ---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 17. OPERATIONS SPECIFICATIONS AIRCRAFT MAINTENANCE

- MARTIN M-202/404 Form Approved.

UNITED STATES OF AMERICA Budget Bureau

FEDERAL AVIATION AGENCY No. 04-R075.

WASHINGTON PART D PAGE 1 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE MARTIN M-202/404 Overhaul Inspection & Period Check Period Air Conditioning, Chapter 21 12,000 Actuators & Valves 6,000 Blower, Cabin 2,000 Blower, Combustion Air 3,000 Box, Cabin Temperature Control 4,000 Control, Fuel Assembly 4,000 Heater Unit 2,500 Ignition Units 2,500 Solenoid Valves & Filters 4,000 Switches, Ram Air 6,000 Turbo Compressor 2,000 Auto-Pilot, Chapter 22 12,000 Electrical, Chapter 24 12,000 Ammeter & Voltmeter 6,000 Contactor, Generator 2,000 Control Panel, Generator 2,000 Generator EC Inverter, Emergency 5,000 Inverter, Main 2,000 Regulator, Voltage 2,000 Relay, Battery 6,000 Equipment & Furnishings, Chapter 25 12,000 Chute, Evacuation OC First-Aid Kit 6 months Fire Protection, Chapter 26 12,000 Cylinders * Panel, Fire Detector 6,000 * Hydrostatic and life limits shall be entered here and shall not exceed those set forth in Part 173, Chapter I, Subtitle "B" of CFR Title 49.

Flight Controls, Chapter 27 12,000 Actuator, Stabilizer Jack 8,000 Indicator, Wing Flap Position 6,000 Transmitter, Wing Flap Position 6,000

Fuel, Chapter 28 12,000 Indicator, Fuel Quantity 4,000 Pump, Fuel Boost 4,000 Transmitter, Fuel Quantity 4,000 Effective date _____________________ PAGE 2 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE MARTIN M-202/404 Overhaul Inspection & Period Check Period Hydraulic, Chapter 29 12,000 Accumulator 8,000 Indicator, Hydraulic Pressure 6,000 Pump, Auxiliary Hydraulic 6,000 Regulator, Pressure 6,000 Transmitter, Hydraulic Pressure 6,000 Ice & Rain, Chapter 30 12,000 Heater, Wing & Empennage 3,000 Unit, Windshield Wiper 8,000 Units, Ignition 3,000 Instruments, Chapter 31 12,000 Clock OC Landing Gear, Chapter 32 12,000 Bottle, Emergency Air * Motor, Nose Dampener 4,000 Wheels, Tires & Brakes OC Lights, Chapter 33 12,000 Flasher 4,000 Navigation, Chapter 34 12,000 Altimeter 3,000 ** Compass, Magnetic 6,000 Gyro, Directional 1,500 Indicator, Air Speed 4,000 Indicator, Gyro Horizon 3,000 Indicator, Outside Air Temperature 6,000

Indicator, Rate of Climb 4,000 Indicator, Turn & Bank 3,000 ** Bench Check every 12 months.

Oxygen, Chapter 35 12,000 Bottle, Oxygen * Regulator, Pressure 8,000 * Hydrostatic and life limits shall be entered here and shall not exceed those set forth in Part 173, Chapter I, Subtitle "B" of CFR Title 49.

Effective date _____________________ PAGE 3 of 3 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE MARTIN M-202/404 Overhaul Inspection & Period Check Period Fuselage, Chapter 53 12000 Nacelles, Chapter 54 12000 Stabilizers, Chapter 55 12000 Wings, Chapter 57 12000 Effective date _____________________ ---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 18. OPERATIONS SPECIFICATIONS AIRCRAFT MAINTENANCE

- VISCOUNT - 745D/810 Form Approved.

UNITED STATES OF AMERICA Budget Bureau FEDERAL AVIATION AGENCY No. 04-R075.

WASHINGTON PART D Page 1 of 3 pages

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE VISCOUNT 745D/810 Overhaul Inspection & Period Check Period Air-Conditioning System, Chapter 21 12000 Actuator, Cabin Hot Air Supply 3500 Actuator, Cabin Temperature Control 3500 Actuator, Intercooler Flap 3500 Actuator, Spill Valve Actuator 2500 Actuator, Unpressurized Flight Valve 3500 Altimeter, Cabin 6000 Blower, Cabin Vent 2500 Blower, Centrifugal Combustor 1500 Compressor, Cabin Air 2000 Controller, Cabin Pressure 4000 Controller, Mass Flow 4000 Heater Assembly 2500 Ignition Assembly 2500 Indicator, Cabin Differential Pressure 4000 Pump, Heater Fuel 2500 Switch, Cycling 2500 Switch, Thermal 2500 Turbine, Cabin Air Cooling 4000 Valve, Cabin Outflow 4000 Valve, Duct Relief 6000 Valve, Safety 6000 Auto-Pilot, Chapter 22 12000 Amplifier, Flux-Gate 4000 Amplifier & Signal Generator 3500 Computer, Flight Path 1500 Controller, Pedestal 6000 Indicator, Master Direction 4000 Indicator, Three Axis Trim 4000 Switch, Gaging o/c Servo, Main 3500 Transmitter, Flux-Gate 4000 Vertical Dynamic Sensor o/c Electrical System, Chapter 24 12000 Circuit Breaker, Differential Overload 3500 Generator o/c Inverter, Emergency 5000 Inverter, Main 2000 Regulator, Voltage 2000 Switch, Inverter Warning Failure 4000