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 322–333
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hours time in service.

"D" Inspection/Check * To be accomplished at intervals not exceeding seven thousand (7000) hours time in service. (One-fourth of fleet at 7000, one-fourth of fleet at 14,000, one-fourth at 21,000, and one-fourth of fleet at 28,000).

NOTE:

* Revision to the times specified for the "A", "B", and "C" checks can be initiated after accumulation of satisfactory service experience by the submission of an amended Operations Specifications - Maintenance to the assigned inspector for consideration, handling, and approval.

** The "D" inspection is based on the premise that the details of the "A", "B", and "C" checks will be developed in sufficient depth to assure the airworthiness of the aircraft until the "D" inspection interval is reached.

Effective date __________________ Page 2 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Air Conditioning, Chapter 21 O.C. A,B,C,D Valve - Ram Air O.C. C Fan - Heat Exchanger Cooling Air 7000 C,D Actuator - Valve, Cabin Air Outflow 7000 C,D Controller - Cabin Pressure O.C. C,D Regulator - Reset, Cabin Pressure Control 12,500 D Valve - Safety, Cabin Pressure 14,000 C,D Valve - Pressure Regulator, Air Condition 14,000 C,D Valve - Flow Control, Air Conditioning 12,500 C,D Sensor - Pressure Differential, Cabin to Reference O.C. C Indicator - Pressure, Air Conditioning Supply O.C. C,D Indicator - Cabin Rate of Climb O.C. C,D

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Indicator - Cabin Differential Pressure and Altitude O.C. C,D Turbine - Cooling 7000 C,D Fan - Cooling, Radio Rack 7000 C,D Switch - Differential Pressure, Fan O.C. C,D Indicator - Position, Temp. Control Valve O.C. C,D Transmitter - Temp. Control Valve, Position O.C. C,D Indicator - Cabin Duct Temperature O.C. C,D Thermostat - Water, Separator Discharge 7000 C,D Valve - Temperature Control, Water Separator 12,500 C,D Auto Pilot, Chapter 22 O.C. A,B,C,D Computer - Pitch Axis 7000 C,D Computer - Roll Axis 7000 C,D Computer - Stability Augmentation 7000 C,D Actuator, Mach Trim and Yaw Damper 7000 C Drive - Elevator and Aileron Servo 7000 C Panel - Controller O.C. B,D Indicator - Trim O.C. B,D Computer - Air Data O.C. B,D Communications, Chapter 23 The Maintenance Program (overhaul time and intermediate checks) for this chapter is to be established in the local Air Carrier District Office for all units of the communication systems.

Effective date ____________________ Page 3 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Electrical System, Chapter 24 O.C. A,B,C,D Transmission - Constant Speed Drive 3000 B Heat Exchanger - Constant Speed Drive Oil Temperature O.C. C Indicator - Constant Speed Drive Oil Temperature O.C. C,D Generator, AC 40KVA 3000 B Panel, Generator Control O.C. C,D Panel, Bus Control O.C. C,D Regulator, Voltage O.C. C,D Relay - Generator, External Power,

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AC, Crosstie, APU 7000 C Inverter Emergency O.C. C,D Transformer Rectifier O.C. C,D Battery Charger O.C. C,D Loadmeter (AC and DC) O.C. C,D AC Voltmeter O.C. C,D Frequency Meter O.C. C,D Battery O.C. C,D DC Volt/Ammeter O.C. C,D Equipment and Furnishings, Chapter 25 O.C. A,B,C,D Emergency Equipment O.C. A,B,C,D Coffeemaker O.C.

Seat Belts O.C. A,B,C,D Fire Protection, Chapter 26 O.C. A,B,C,D Fire Detector O.C. B Control - Fire Warning Bell O.C. B Control - Fire Warning Horn, APU O.C. B Container - Fire Extinguisher 5 years C,D Cartridge - Dual Squib 4 years C,D Flight Controls, Chapter 27 O.C. A,B,C,D Actuator Aileron Trim O.C. C,D Damper - Aileron and Elevator 14,000 C,D Valve - Power Shutoff, Rudder Hydraulic 14,000 C,D Damper - Rudder 14,000 C,D Feel Spring - Rudder Trim and Load O.C.

Power Package - Hydraulic Rudder Control 14,000 C,D Actuator Limiter - "Q" Bellows, Rudder Throw O.C. C,D Effective date ____________________ Page 4 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Flight Controls, Chapter 27, continued O.C. A,B,C,D Valve - Elevator Control 14,000 C,D Valve - Hydraulic Return Relief 14,000 C,D Valve - Hydraulic Pressure Reducer and Bleed 14,000 C,D Cylinder - Elevator Power Control 14,000 C,D Accumulator - Hydraulic O.C. C,D

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Switch - Elevator Press. Low O.C. C,D Motor Actuator - Primary Longitudinal Trim 14,000 C,D Motor Actuator - Alternate Longitudinal Trim 14,000 C,D Jack Screw 14,000 C,D Box - Longitudinal Trim Gear 14,000 C,D Valve - Wing Flap Control 14,000 C,D Cylinder - Wing Flap Actuating 14,000 C,D Transmitter - Flap Position O.C. C,D Indicator - Flap Position, Dual O.C. C,D Actuator - Ground Spoiler, Automatic 14,000 C,D Valve - Ground Spoiler Control 14,000 C,D Cylinder - Actuating Ground Spoiler 14,000 C,D Actuator - Spoiler Flight 14,000 C,D Fuel System, Chapter 28 O.C. A,B,C,D Pump - Boost Fuel 7000 C Pump - Engine Start 7000 C,D Valve - Pressure, Crossfeed (Mech) 14,000 C,D Valve - Engine Fuel Fire Shutoff 14,000 C,D Valve - APU - Fuel Shutoff (Solenoid) 14,000 C,D Indicator - Fuel Quantity Master O.C. C,D Indicator - Repeater, Fuel Quantity O.C. C,D Indicator - Totalizer, Fuel Quantity O.C. C,D Probe - Fuel Quantity O.C. D Valve - Fuel Fill 14,000 C,D Hydraulic System, Chapter 29 O.C. A,B,C,D Pump - Hydraulic - Engine Driven 4000 B Pump - Hydraulic - Electric, Auxiliary 4000 B Motor Pump - Reversible 14,000 B Pump - Hand - Ground Service O.C. C Reservoir - Hydraulic System O.C. C,D Accumulator O.C. C,D Valve - Priority 14,000 C Valve - Spoiler Shutoff and System Depressurization O.C. C Valve - Engine Driven Pump Fire Shutoff 14,000 C Filters O.C. C Effective date ____________________ Page 5 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overall Inspection Period & Check

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Period Hydraulic System, Chapter 29, continued O.C. A,B,C,D Indicator - Fluid Quantity - Hydraulic O.C. C,D Transmitter - Fluid Quantity O.C. C,D Indicator - Hydraulic Pressure O.C. C,D Transmitter - Hydraulic Pressure O.C. C,D Switch - Warning - Hydraulic System Low Pressure O.C. C,D Thermoswitch - Over Temp Hydraulic Fluid O.C. C,D Ice and Rain Protection, Chapter 30 O.C. A,B,C,D Tail De-icer Timer 7000 C High Pressure Switches O.C. C,D Pressure Regulator & Shutoff Valves 7000 C Temperature Sensors O.C. C Air Intakes O.C. A,C,D Pitot and Static O.C. B,C,D Wiper and Rain Repellent O.C. C,D Motor 14,000 C,D Water Lines O.C. C Instruments, Chapter 31 O.C. A,B,C,D The Maintenance Program (overhaul time and intermediate checks) for this chapter is to be established in the local Air Carrier District Office for all units in this system including the flight recorder.

Landing Gear, Chapter 32 O.C. A,B,C,D Main Landing Gear 7000 A,B,C,D Nose Landing Gear 7000 A,B,C,D Hydraulic Control System 14,000 C,D Hydraulic Control System (Wheels and Brakes) O.C. C Hydraulic Brake Control Valve 14,000 C Accumulators O.C. A,B Brake Fluid Quantity Limiter 7000 C,D Anti-skid System O.C. C,D Control Box O.C. C,D Wheels O.C. B Brakes O.C. B Steering Hydraulic Controls O.C. C,D Steering Control Valve 14,000 C,D Bypass & Relief Valve 14,000 C,D Steering Cylinder 14,000 C,D Nose Wheel Swivel Glands O.C. C,D Positioning and Warning O.C. A,B,C,D Effective date ___________________ Page 6 of 10

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OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Lights, Chapter 33 O.C. A,B,C,D Lights - Flight Compartment O.C. B,C,D Navigational Lights - Wing Tip O.C. C,D Lights - Anti-collision O.C. A,B Lights - Landing and Taxi O.C. A,B Battery Pack - Cabin Emergency Lights O.C. B Light - Pilot's Emergency Portable O.C. C Navigation, Chapter 34 O.C. A,B,C,D The Maintenance Program (overhaul time and intermediate checks) for this chapter is to be established in the local Air Carrier District Office for all units in this system.

Oxygen System, Chapter 35 O.C. A,B,C,D Cylinder, Oxygen, Crew O.C. B Regulator - Oxygen, Crew Cylinder, Crew Pressure 14,000 B,D Regulator - Oxygen, Crew Pressure Breathing 14,000 B,D Cylinder - Oxygen, Passenger Pressure O.C. Hyst. 5 yrs Regulator - Oxygen, Passenger Pressure 14,000 C,D Cylinder - Oxygen, Attendants and Crew Portable O.C. Hyst. 5 yrs Pneumatic, Chapter 36 O.C. A,B,C,D Valve - Pneumatic Crossfeed 14,000 C,D Valve - Check, Pneumatic and APU 8th Stage E.O. C Valve - Augmentation 7000 C,D Regulator - Pneumatic Pilot Pressure 7000 C,D Valve - Ground Connection & Check Pneumatic O.C. C,D Control - Ice Protection Anticipation O.C. C,D Indicator - Pneumatic Pressure O.C. C,D Transmitter - Pneumatic Pressure O.C. C,D Sensor - Overheat, Tail Compartment O.C. C,D Water and Waste, Chapter 38 O.C. A,B,C,D Water Supply O.C. A,B,C,D Waste Disposal O.C. A,B,C,D Effective date ____________________ Page 7 of 10

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OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Airborne Auxiliary Power, Chapter 49 O.C. A,B,C,D Gas Turbine 2200* B,C,D Combustion Chambers 1100* Unit & Low Pressure Filters 500* C Acceleration & Overtemp Control Thermostat O.C. C,D Ignition Plug 500* C,D Starter Motor 2200* C,D Load Control Thermostat O.C. C,D Centrifugal Switch 2200* C,D Generator - Tach O.C. B,C Oil Filter C * Operating Time for Unit - NOT aircraft time.

Oil Change to be at Manufacturer recommendations.

Structures, Chapter 51 O.C. A,B,C,D Doors, Chapter 52 O.C. A,B,C,D Snubber - Forward Entrance Door O.C. B Motor - Stairway Gearbox Actuator O.C. B,C Motor - Stairway Handrail O.C. B,C Cylinder - Retract, Ventral Stairs O.C. C Valve - Ventral Stair O.C. C Passenger Aft Entrance Door 7,000 B,C,D Main Gear Support Fittings and Auxiliary Spars 2500 B,C,D Emergency Exit Doors, Zone 58 (LH and RH) 7000 B,C,D Forward Passenger Entrance and Service Door 7000 B,C,D Electrical and Electronics Compartment Door 14,000 B,C,D Baggage Compartment Doors 7000 Framing Around Main Cargo Door 14,000 Main Cargo Door 28,000 Fuselage, Chapter 53 O.C. A,B,C,D Radome and Pressure Bulkhead 7000 A,B,C,D Bulkhead Station 786 Internal Structure 28,000 C,D Floor Beams Station 69 to 148 28,000 C,D Top of Center Section - Center Aisle Between Inboard Seat Tracks and Sides 28,000 C,D Fuselage Internal Structure 28,000 C,D Rear Baggage Compartment Interior 28,000 C,D

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Effective date ____________________ Page 8 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Fuselage, Chapter 53, continued O.C. A,B,C,D Forward Baggage Compartment Interior 28,000 B,C Body Station 642 Bulkhead 28,000 C,D Nose Wheel Well - Canted Panel - Support Beams and Adjacent Area 28,000 A,B,C,D Fuselage Interior Structure Production Splice 817 to 908 7000 D Nacelle and Pylons, Chapter 54 O.C. A,B,C,D Firewall, Pylon, and Engine Mount Fittings 7000 Fuselage Bulkhead and Pylon Spar Stubs 7000 C,D Pylon Spar and Structure, Station 786 7000 C,D Stabilizers, Chapter 55 O.C. A,B,C,D Elevator Hinge Attachment, Dampers and Adjacent Structure 7000 B,C,D Vertical Stabilizer Installation and Dorsal Fin Structure 7000 B,C,D Stabilizer Outer Panel to Center Section Joints, Upper and Lower Surfaces 7000 B,C,D Rudder Spar and Adjacent Internal Structure Horizontal Stabilizer 7000 B,C,D Vertical Stabilizer Leading Edge Interior 14,000 Elevator Front and Rear Spars, Elevator Interior Structure, Elevator Tabs 28,000 B,C,D Horizontal Stabilizer Leading Edge, Tip, Front Spar and Interior 28,000 C,D Windows, Chapter 56 O.C. A,B,C,D Windshield, LH and RH O.C. A,B,C Window - Cockpit LH and RH Sliding O.C. A,B,C Window - Cockpit LH and RH - Aft O.C. A,B,C Window - Eyebrow LH and RH O.C. A,B,C Windshield - Center O.C. A,B,C Wings, Chapter 57 O.C. A,B,C,D Wing Leading Edge Interior 7000 C,D Wing Tip - Interior 14,000 C,D

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Wing to Fuselage Upper Attach Angle 14,000 Station 484-645 7000 C,D Wing Flaps - Internal 14,000 C,D Wing Internal 14,000 Front Spar - Wing Center Section 28,000 C,D Effective date ____________________ Page 9 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Powerplant, Chapter 71 O.C. A,B,C,D Nose Cowl O.C. A,B,C Engine Turbine, Chapter 72 4800 Engine Fuel and Control, Chapter 73 O.C. A,B,C,D Fuel Heater Valve 7000 B Fuel Heater O.C. B,C Fuel Pump O.C. B,C Valve - Pressurizing and Dump O.C. B,C De-icer Timer O.C. B Fuel Control O.C. B,C Indicator - Fuel Temperature O.C. B,C Indicator - Fuel Flow O.C. B,C Power Supply, Fuel Flow O.C. C Switch - Low Fuel Press. O.C. C Transmitter - Fuel Flow 7000 B,C Eductor - Fuel Vapor O.C. B,C Air, Chapter 75 O.C. A,B,C,D Valve - Engine Anti-ice 7,000 C Valve - Shutoff, Cowl Anti-icing 7,000 C Valve - Thermostat Control, Cowl Anti-icing O.C. C Engine Controls, Chapter 76 O.C. A,B,C,D Engine Indicating, Chapter 77 O.C. A,B,C,D Generator - Tachometer N1 and N2 O.C. C Indicator - Tachometer N1 and N2 O.C. C Transmitter - Engine Press Ratio O.C. C Indicator - Engine Press Ratio O.C. C Monitor - AVM O.C. B,C Indicator - AVM O.C. B,C

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Pick-Up AVM O.C. B,C Indicator - Exhaust Gas Temp O.C. C Effective date ____________________ Page 10 of 10

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE DOUGLAS DC-9 Overhaul Inspection Period & Check Period Exhaust, Chapter 78 O.C. A,B,C,D Gauge - Accumulator Pressure O.C. B,C Accumulator, Thrust Reverser O.C. B,D Actuator - Thrust Reverser Bucket O.C. B Indicating - Thrust Reverser System O.C. C Switch - Low Pressure Warning O.C. C Reverser - Thrust and Exhaust Nozzle E.O. B,C Valve - Control, Thrust Reverser O.C. B,C Oil, Chapter 79 O.C. A,B,C,D Cooler - Engine Fuel/Oil O.C. B,C Sensor, Oil Temperature O.C. B,C Indicator - Oil Pressure O.C. C Indicator - Oil Quantity O.C. C Indicator - Oil Temperature O.C. C Switch - Low Pressure Warning O.C. B,C Transmitter - Oil Pressure O.C. B,C Switch - Filter Differential Pressure O.C. B,C Transmitter - Oil Quantity O.C. @@@ Starting, Chapter 80 O.C. A,B,C,D Starter - Pneumatic 7000 B,C Valve - Regulating Shutoff, Air Starter 7000 B Switch - Starter Control O.C. B Ignition - Exciter 12,000 B,C Igniter Plugs 2000 B,C Effective date ____________________ ---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 40. OPERATIONS SPECIFICATIONS, AIRCRAFT MAINTENANCE - HAWKER SIDDELEY 748 SERIES 2A Form Approved.

UNITED STATES OF AMERICA Budget Bureau

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FEDERAL AVIATION AGENCY No. 04 R075.

WASHINGTON PART D Page 1 of 9

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE - GENERAL HAWKER SIDDELEY 748 SERIES 2A Thorough inspection shall be accomplished in accordance with the applicable procedures as listed in ABC Airlines Maintenance Manual.

Preflight (Pre/Flt) shall be accomplished each service calendar day. Inspection shall be in accordance with the applicable procedures listed in ABC Airlines Maintenance Manual.

Special Inspections.

The frequency and procedure for performing special inspections will be accomplished as specified in the operator's maintenance manual.

Overhaul and inspection/check period time limitations specified in hours and calendar time are maximum limits of whichever occurs first.

Check A Inspections. To be accomplished within 100 hours of aircraft time in service since last check.

Period Inspections. (PI) The procedure for the performance of period inspections will be accomplished as specified in ABC Airlines Maintenance Manual. Period inspections must be accomplished at intervals not to exceed 500 hours of aircraft time in service. The #1 period inspection will be accomplished each 500 hours of aircraft time in service or 90 days, whichever occurs first.

Aircraft shall not be utilized in air carrier or commercial operations unless:

a. The aircraft and its component parts, accessories, and appliances are maintained in an airworthy condition in accordance with the schedule of maintenance and inspection functions and procedures set forth in the operator's maintenance manual.

b. OC "On Condition" items will be maintained in continuous airworthiness condition by periodic and progressive inspections, checks, services, repair, and/or preventive maintenance and shall be appropriately described in the

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operator's maintenance manual.

c. Parts or subcomponents not listed below will be checked, inspected and/or overhauled at the same time limits specified for the component or accessory to which such parts or subcomponents are related.

Effective date ____________________ Page 2 of 9

OPERATIONS SPECIFICATIONS

AIRCRAFT MAINTENANCE - GENERAL HAWKER SIDDELEY 748 SERIES 2A Abbreviations used in the HS/748 Series 2A maintenance specifications are defined as follows:

PI - Indicates "Period Inspection" PRE/FLT - Indicates "Preflight Inspection" FC - Indicates "Functional Check" BC - Indicates "Bench Check" EO - Indicates "Engine Overhaul" EC - Indicates "Engine Change" OC - Indicates "On Condition" HYD - Indicates "Hydrostatic Test" CALIB - Indicates "Calibration" Life Limited Components The service life limits for aircraft structural parts and components which are fatigue critical are listed in the Hawker Siddeley 748 Recommended Maintenance Schedule, Pages 12 to 18 inclusive. Engine and propeller life limited parts are listed in the Hawker Siddeley 748 Recommended Maintenance Schedule, and may not be changed without CAA or FAA approval.

* These items do not have a set overhaul period. If the unit becomes defective before the quoted hours the unit is repaired.

If the defect occurs after the quoted hours the unit is overhauled.

** 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.

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