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 95–106
Page 107Open in PDF

Switch, Reservoir Feed Pump Pressure Warning 7,000 Slip Tube Assembly, Drip Stick O.C.

Screen Assembly, Filler Adapter O.C.

Scroll, Fuel Boost Pump Feed & Transfer O.C.

Effective date November 6, 1964 Page 7 of 20 Pages

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Fuel System, Chapter 28 continued Swivel, Fuel Dump O.C.

Transmitter, Densitometer O.C.

Transmitter, Fuel Quantity O.C.

Valve, Fire Wall Shutoff 14,000 Valve, Fuel Tank Selector 7,000 Valve, Auxiliary Tank Selector 15,000 Valve, Crossfeed 15,000 Valve, Refueling Manifold Shutoff 17,500 Valve, Tank Fill Control 10,500 Valve, Fuel Dump 15,000 Valve, Fuel Tank Sump Drain O.C.

Valve, Single Float Level Pilot 7,000 Valve, Check with Screen Inlet O.C.

Valve, Feed Pump Shuttle 7,000 Valve, Swing Check O.C.

Hydraulic Power, Chapter 29 Accumulator, Hydraulic System 17,500 Manifold Assembly, Right-Hand Hydraulic Power O.C.

Manifold Assembly, Left-Hand Hydraulic Power O.C.

Pump, Engine Driven Hydraulic 4,000 Pump Assembly, Auxiliary Hydraulic 7,000 Reservoir Assembly, Hydraulic System O.C.

Relief Valve, Hydraulic Reservoir 14,000 Selector Valve, By Pass & Auxiliary Pump 14,000 Valve Assembly, Reservoir Pressure Aspirator 7,000

Page 108Open in PDF

Valve, Auxiliary Pump Selector 14,000 Valve, Auxiliary Hydraulic System Relief 14,000 Valve Assembly, System Filter & Relief 14,000 Valve, Hydraulic Fire Shutoff 14,000 Ice & Rain Protection, Chapter 30 Amplifier, Windshield Temperature Control O.C.

Ammeter, Pitot Heater O.C.

Heater, PT2 Probe O.C.

Nacelle Anti Ice & Outer Wing Shutoff Valve 10,500 Effective date November 6, 1964 PAGE 8 of 20 PAGES

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Ice & Rain Protection, Chapter 30 (continued) Probe Ice Detector OC Switch, Tail Duct Differential Pressure 17,500 Switch, Nacelle Lip Pressure 10,000 Timer, Airfoil Deicing 7,000 Transformer, Windshield Heat OC Valve, Outer Wing & Empennage Deicing OC Valve, Wing Vent Scoop Anti-Ice Shutoff 12,500 Valve, Inner Wing De-Ice OC Valve, Empennage Ice Protection Shutoff 10,500 Valve, Fuselage Air Scoop Anti-Ice Shutoff 10,500 Valve, Windshield Rain Removal 15,000 Instruments, Chapter 31 May be determined by assigned inspector.

Landing Gear, Chapter 32 Axle Nose Gear 12,500

Page 109Open in PDF

Accumulator, Nose Wheel Steering 15,000 Bogie Beam Assembly Including Axles & Pivot Pins 12,500 Bleeder Valve, Nose Wheel Steering OC Box, Anti-Skid Control 3,500 Cylinder Assembly, Main Gear Actuating 12,500 Cylinder Assembly, Brake Lockout 12,500 Cylinder Assembly, Bogie Trim 12,500 Cylinder Assembly, Main Gear Swivel Lock 12,500 Check Valves, Restrictor & Orifice OC Cylinder Assembly, Main Gear Door Latch 12,500 Cylinder Assembly, Main Gear Inboard Door Operating 12,500 Cylinder Assembly, Main Gear Uplatch 12,500 Cylinder Assembly, Nose Gear Retract 12,500 Cylinder Assembly, Nose Gear Uplatch 12,500 Cylinder Assembly, Nose Gear Bungee 12,500 Cylinder Assembly, Nose Wheel Steering 12,500 Detector, Skid 3,500 Emergency Air Brake Bottle * Emergency Air Brake Control OC Gland Assembly, Main Gear Retract Cylinder 12,500 * 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 9 of 20 Pages

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Landing Gear, Chapter 32 continued Gland Assembly, Main Gear Pivot 12,500 Gauge, Emergency Air Brake Bottle O.C.

Gland Assembly, Nose Gear Upper 12,500 Gland Assembly, Nose Wheel Steering Swivel 12,500

Page 110Open in PDF

Gauge, Nose Wheel Steering Accumulator 15,000 Gear Lever, Down Limit Switch 7,000 High Pressure Hose Assemblies O.C.

Horn, Landing Gear Warning 17,500 Indicator, System Brake Pressure O.C.

Main Landing Gear Structural Components Including Attachment to Aircraft 12,500 Manifold, Forward Hydraulic Pressure 12,500 Manifold, Aft Hydraulic Pressure 12,500 Manifold Assembly, Aft Brake 12,500 Main Gear Air Valve O.C.

Main Gear Swivel Lock Assembly 12,500 Main Gear Brake Links & Attachments 12,500 Main Gear Wheel Assembly O.C.

Main Gear Brake Assembly O.C.

Main Gear Side Brake Assembly 12,500 Main Gear Uplatch Assembly 12,500 Main Gear Doors O.C.

Main Gear Door Latching Mechanism 12,500 Main Gear Downlock Visual Indicator O.C.

Nose Gear Shock Strut Assembly 12,500 Nose Gear Drag & Side Brake Assemblies 12,500 Nose Gear Wheel Assembly O.C.

Nose Gear Torque Arm Assembly 12,500 Nose Gear Anti-Retract Mechanism 12,500 Nose Gear Doors O.C.

Nose Gear Door Operating Linkage 14,000 Relays Landing Gear System 7,000 Switch, Nose Oleo Ground Control 7,000 Tires, Nose and Main O.C.

Transmitter, Emergency Air Brake Pressure 7,000 Valve Assembly, Trim Cylinder Relief 12,500 Valve Assembly, Main Gear Door Control 12,500 Valve Assembly, Main Gear Door Manual Operation 12,500 Valve Assembly, Main Gear Bungee Shuttle 12,500 Effective date November 6, 1964 PAGE 10 of 20 PAGES

OPERATIONS SPECIFICATIONS

Page 111Open in PDF

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Landing Gear, Chapter 32 (continued) Valve Assembly, Bogie Lock 12,500 Valve Assembly, Nose Gear Control 12,500 Valve Assembly, Nose Wheel Steering Control 12,500 Valve Assembly, Nose Wheel Steering Relief 12,500 Valve, Anti-Skid Control 3,500 Warning Switches, Gear & Doors 7,000 Warning Horn Cut-Off Switch OC Lights, Chapter 33 May be determined by assigned inspector.

Navigation, Chapter 34 May be determined by assigned inspector.

Oxygen System, Chapter 35 Cylinder, Oxygen, Crew & Passenger System * Door Actuator Check Valve OC Outlet, Passenger Oxygen Valve OC Outlet, First Aid Valve, Passenger Oxygen OC Regulator Assembly, Crew Cylinder Oxygen Pressure 5,000 Regulator, Crew Oxygen 7,500 Regulator and Automatic Opening Valve, Passenger Oxygen 5,000 Regulator, First Aid Oxygen Cylinder 5,000 Relay, Oxygen Time Delay 5,000 Switch Oxygen Altitude 7,500 Valve, First Aid Supply Passenger Oxygen OC Valve, Oxygen Surge 5,000 Pneumatic System, Chapter 36 Amplifier, Pneumatic Temperature Control 12,500 Actuator, Bleed Air Heat Exchanger EO Bulb, Manifold Air Temperature OC Connector, Pneumatic Duct OC Door Assembly, Bleed Air Heat

Page 112Open in PDF

Exchanger Exit OC Heat Exchanger, Bleed Air 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.

Effective date _____________________ Page 11 of 20

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Pneumatic System, Chapter 36 continued Indicator, Air Supply Temperature OC Relay, Low Pressure Pneumatic OC Switch, Manifold Under Pressure 14,000 Switch, Manifold Rupture Warning OC Temperature Thermistor OC Thermo Switches, Over and Under Temperature OC Valve, Pneumatic Pressure Regulator EO Valve, Bleed Air Pressure Relief EO Valve Assembly, First Spool Bleed Air Shutoff and Check 7,000 Valve, Pneumatic Fire Shutoff 14,000 Valve, Pneumatic Crossfeed 7,500 Valve, Ground Pneumatic Supply OC Doors, Chapter 52 Cylinder Assembly, Door Snubber 14,000 Door Assembly, Turbo Compressor Access OC Main Cabin Cargo Door Hydraulic System OC Cylinder Assembly, Main Cabin Door Actuating OC Powerplant General, Chapter 71 Links, Engine Mount 3EO

Page 113Open in PDF

Engine, Chapter 72 Compressor Section 3,000* Turbine Section 2,000* Engine Fuel and Control, Chapter 73 Engine Fuel Filter Element 100 Fuel & Oil Heat Exchanger 2EO Fuel Pump Pressure Warning Switch OC Fuel Boost Pump, Engine Driven 2EO Fuel Flow Indicator 3,500 Fuel Flow Transmitter EO Fuel Pressure Indicator 10,500 Fuel Pressure Transmitter 7,000 * Sample one turbine section overhaul at 1800 hours, one compressor section overhaul at 2400 hours, and one compressor section overhaul at 2800 hours.

Effective date _____________________ Page 12 of 20 Pages

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Engine Ignition, Chapter 74 Switch, Ignition Arming OC Switch, Ignition Override OC Switch, Fuel Lever Control OC Timer 7,000 Engine Air, Chapter 75 Valve, Assembly, Jet Pump 6,000 Valve, Accessory Compartment Cooling Shutoff OC Engine Controls, Chapter 76 Lever, Power Control OC Lever, Fuel Shutoff OC Sector, Engine Power Control OC Engine Indicating, Chapter 77

Page 114Open in PDF

Generator, Tachometer 3,500 Indicator, Engine RPM 7,000 Indicator, Engine Pressure Ratio OC Indicator, Engine Exhaust Gas Temperature 7,000 Pickup, PT2 Pressure OC Transmitter, Pressure Ratio 3,500 Exhaust, Reverser & Thrust Brake, Chapter 78 Aft Nozzle Cowl EO Ejector & Reverser 3,500 Ejector Operating Mechanism 5,000 Exhaust Nozzle EO Pneumatic Components Attached to & Related to the Ejector Reverser 3,500 Retractable Ejector Alternate Air System OC Oil System, Chapter 79 Actuator, Oil Cooler Exit Door EO Bulb, Oil Temperature OC Cooler, Engine Oil EO Indicator, Constant Speed Drive Oil Temperature 10,000 Indicator, Engine Oil Pressure EO Indicator, Engine Oil Quantity 7,500 Indicator, Oil Temperature 10,000 Oil Tank 2EO Effective date _____________________ Page 13 of 20 Pages

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Oil System, Chapter 79 continued Switch, Constant Speed Drive Oil Level 7,000 Switch, Oil Cooler Door OC Switch, Oil Pressure Warning OC

Page 115Open in PDF

Thermostat, Oil Temperature Control EO Transmitter, Engine Oil Pressure EO Transmitter, Engine Oil Quantity OC Valve, Engine Oil Shutoff Valve, Constant Speed Drive Oil Shutoff OC Valve, Oil Temperature Control OC Engine Starting, Chapter 80 Starter, Engine Air Turbine EO Valve, Starter Air Shutoff 2EO Water Injection, Chapter 82 Adapter, Auxiliary Water Fill OC Cap, Auxiliary Water Fill OC Cell Assembly, Water OC Pump, Water Injection 2EO Relay, Water Injection & Fill Control OC Switch, Water Injection Fill & Drain OC Switch, Water Level OC Switch, Water Injection Arming OC Switch, Water Pressure Warning OC Valve, Water Shutoff 12,500 Valve, Engine Water Line Filling 14,000 Valve, Compressor Water Injection 14,000 Valve, Water Drain & Purge 14,000 Valve, Water Injection Relief 7,000 Valve, Tank Pressurization & Drain 7,000 Valve, Pressure Fill OC Valve, Tank Drain 7,000 Effective date _____________________ Page 14 of 20

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Structure Inspection Program The aircraft structure is divided into zones and a detailed inspection time limitation is listed for each zone. The inspection of the zone shall include all areas of structure, installation of components and appliances unless a specific time limitation is listed otherwise for a particular item.

Page 116Open in PDF

E Check - 4,000 Hours Overhaul Inspection & D Check - 500 Hours Period Check Period Demountable Powerplant Aft Surface of Nose Cowl, Firewall, Engine Control and Accessory Brackets. Zone 1, 2, 3, & 4 D Wings Wing Tip Zone 5 L/R 5E D Wing Outboard of Sta. Xrs 727 Zone 6 L/R 5E Wing Leading Edge Sta. Xfs 710 to Xw 761 Zone 7 L/R E Wing Leading Edge Sta. Xw 485 to Xfs 710 Zone 8 L/R E No. 1 & 4 Alternate Fuel Tanks Zone 9 L/R 5E Wing Trailing Edge Sta. Xw 408 to Xw 761 Aileron Hinge Aft of Rear Spar Zone 10 L/R E Brackets 4D & Bolts Aileron and Tab Zone 11 L/R E Hinges & 4D Attachments Aileron Leading Edge Balance Weights 2E Wing Leading Edge at Outboard Pylon Sta. Xw 454 to Xw 485 Zone 12 L/R E Outboard Pylon, Apron and Nacelle Access Doors Zone 13 L/R 4D Top Side of Upper Spar Zone 13 L/R 2E Inboard Pylon, Apron and Nacelle Access Doors Zone 14 L/R 4D Top Side of Upper Spar Zone 14 L/R 2E Wing Leading Edge Sta. Xw 408 to Xw 454 Zone 15 L/R E Wing Leading Edge Sta. Xw 257 to Xw 408 Zone 16 L/R E No. 1 & 4 Main Fuel Tanks Zone 17 L/R 5E Wing Trailing Edge from Outboard Auxiliary Spar to Sta. Xw 408 Zone 18 L/R E Main Landing Gear Support Fittings and Auxiliary Spars Zone 19 L/R 2E Wing Leading Edge at Inboard Pylon Sta. Xw 223 to Xw 257 Zone 20

Page 117Open in PDF

L/R E Effective date _____________________ Page 15 of 20

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Wing Leading Edge Sta. Xfs 107 to Xw 223 Zone 21 L/R E Wing Leading Edge Sta. Xwo to Xfs 107 External Inspection Zone 22 L/R E Internal Inspection Zone 22 L/R 5E No. 2 & 3 Alternate Fuel Tanks Zone 23 L/R 5E No. 2 & 3 Main Fuel Tanks Zone 24 L/R 5E Outboard Wing Flap Interior Structure Zone 25 L/R E Flap Hinge Support Fittings Zone 25 L/R 2E Aft Side of Flap Spar Zone 25 L/R 4E Inboard Wing Flap & Links at the Outboard End of the Flap Which Connect to the Inboard End of the Outboard Flap Zone 26 L/R E Flap Hinge Support Fittings and Aft Side of Flap Spar Zone 26 L/R 4D Interior of Center Wing Sta. Xcw 0 to Xcw 69.5 (Front to Rear Spar) Zone 27 L/R 5E Fuselage Radome Zone 51 E Fuselage Turbo Compressor Compt.

Zone 52 4E Navigation Antenna Compt. Zone 53 E Nose Gear Wheel Well Zone 54 4E Nose Wheel Well Tunnel Zone 55 L/R 4E Air Conditioning Accessory Compt.

Sta. 248 to 310 Zone 56 E Forward Cargo Compartment Sta. 310 to 640 Zone 57 4E

Page 118Open in PDF

Forward Cargo Compartment Tunnel Sta. 310 to 640 Zone 57 L/R 4E Fuselage Accessory Compartment Sta. 640 to 680 Zone 58 E Upper and Lower Front Spar Cap, Forward Face of Front Spar Web, Upper and Lower Front Spar Caps and Splice Plates at Sta. Xcw 0 Zone 58 4E Aft Cargo Compartment Sta. 980 to 1340 Zone 59 4E Aft Cargo Compartment Tunnel Sta.

980 to 1340 Zone 59 L/R 4E Fuselage Belly Compartment Sta.

1337 to Pressure Dome at Sta.

1490 Zone 60 DC-8-50 E Effective date _____________________ Page 16 of 20

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-8/F Overhaul Inspection & Period Check Period Fuselage Fuselage Belly Compartment Sta.

1337 to Pressure Panel at Sta. 1566 Zone 60 DC-8-F only E Aft Fuselage Sta. 1490 to 1690 Zone 61 DC-8-50 E Aft Fuselage Sta. 1566 to 1690 Zone 61 DC-8-F only E Aft Face and Periphery of Pressure Panel at Fuselage Sta. 1566 Zone 61 DC-8-F only E Fuselage Tail Cone Zone 62 E Fuselage Sta. 109 to 123 above Cockpit Floor Zone 63 4E Fuselage Cockpit Sta. 123 to 188 Zone 64 4E Fuselage Cockpit Sta. 188 to 265 Above Floor Zone 65 L/R E Fuselage Sta. 248 to 109 Between Cockpit Floor and Horizontal Pressure Panel Zone 66 E