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Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23

Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23

Name: Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23
SKU: HD-OH6A-TM55-1520-214-23
Availability: InStock

Original price was: $39.95.Current price is: $24.95.

Comprehensive technical manual TM 55-1520-214-23 providing Aviation Unit Maintenance (AVUM) and Aviation Intermediate Maintenance (AVIM) instructions, servicing standards, overhaul schedules, and airframe structural repair data for the Hughes OH-6A Cayuse observation helicopter.

SKU: HD-OH6A-TM55-1520-214-23 Category: Helicopter Manuals Tags: Aviation Unit and Intermediate Maintenance, Hughes OH-6A Cayuse Helicopter, OH-6A Helicopter Service Manual PDF, TM 55-1520-214-23 Maintenance Manual Vendor: Industrial Manual Hub

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Description

This technical publication serves as the official Aviation Unit Maintenance (AVUM) and Aviation Intermediate Maintenance (AVIM) manual for the Hughes OH-6A Cayuse Helicopter, designated under Department of the Army technical manual TM 55-1520-214-23 (incorporating updates through Change 39). Covering airframe assemblies, dynamic drive components, mechanical flight controls, turboshaft powerplant installations, and electrical distribution networks, this manual gives aviation mechanics and maintenance personnel complete depot- and field-level servicing, inspection, and repair instructions.

File Details

Manual Type: Aviation Unit and Intermediate Maintenance Manual (AVUM & AVIM)
Brand: Hughes Helicopters / Department of the Army
Model: OH-6A Cayuse Observation Helicopter (Series 1, Series 2, and Series 3)
Document Number: TM 55-1520-214-23
Publication Date: 31 December 1976 (Includes Changes 1 through 39 updated through November 1992)
Language: English
Format: Digital PDF
Applicable Engines: Allison T63-A-5A / T63-700 Turboshaft Series

Comprehensive Technical Scope & Aircraft Systems

The Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23 details extensive procedures across all structural and mechanical boundaries of the aircraft. Clear mechanical breakdowns, dimensional limits, and rigging standards ensure precision maintenance for the four-bladed fully articulated main rotor group, offset flapping hinges, drive shafts, overrunning clutches, and the two-bladed anti-torque tail rotor system.

Complete PDF Bookmark Tree

Complete Bookmarks

The complete bookmarks in the “Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23” are as follows:

Parts Manual

Maintenance Manualp. 1

Changesp. 2

Change 39p. 2

Change 38p. 3

Change 37p. 4

Change 36p. 6

Change 35p. 7

Change 34p. 8

Change 33p. 9

Change 32p. 10

Change 31p. 11

Change 30p. 12

Change 29p. 13

Change 28p. 14

Change 27p. 17

Change 26p. 18

Change 25p. 19

Change 24p. 20

Change 23p. 21

Change 22p. 22

Change 21p. 23

Change 20p. 25

Change 19p. 26

Change 18p. 27

Change 17p. 28

Change 16p. 29

Change 15p. 30

Change 14

Change 13p. 32

Change 12p. 33

Change 11p. 34

Change 10p. 35

Change 9p. 36

Change 8p. 37

Change 7p. 38

Change 6p. 39

Change 5p. 41

Change 4p. 42

Change 3p. 43

Change 2p. 44

Change 1p. 45

Warning Pagep. 46

Table of Contentsp. 50

Prefacep. 52

Major Componentsp. 53

Ch. 1 AIRCRAFT GENERALp. 56

I – Servicingp. 56

Fig. 1-1 Servicing Pointsp. 57

Table 1-1 Consumable Maintenance Supplies and Materialsp. 66

Table 1-1 Consumable Maintenance Supplies and Materials (con't)p. 67

Table 1-2 National Supply Class Referencep. 72

Table 1-3 Special Tools and Test Equipmentp. 73

Table 1-3 Special Tools and Test Equipment (con't)p. 74

Table 1-4 Support Equipmentp. 74

II – Lubricationp. 75

III – Handling, Jacking, Mooring, Hoisting and Sling Loadingp. 75

Table 1-5 Premaintenance Requirements for General Handling of Aircraftp. 75

Fig. 1-2 Principal Dimensionsp. 76

Fig. 1-3 Hoisting, Jacking and Levelingp. 77

Fig. 1-4 Main Rotor Maintenance Platformp. 78

Fig. 1-5 Folding and Stowing of Main Rotor Bladesp. 79

Fig. 1-6 Ground Handling Wheelsp. 82

Fig. 1-7 Servicing Main Rotor Bladesp. 84

Table 1-6 Approximate Hoisting Weights of Componentsp. 85

IV – Inspection Requirementsp. 86

Fig. 1-8 Area Diagramp. 87

Aircraft Inspection Checksheetp. 88

V – Overhaul and Retirement Schedulep. 107

Table 1-7 Overhaul and Retirement Schedulep. 108

Table 1-7 Overhaul and Retirement Schedule (con't)p. 109

Ch. 2 AIRFRAMEp. 110

Section I – Fuselagep. 110

Fig. 2-1 Access and Inspection Provisionsp. 111

Fig. 2-2 Access and Inspection Provisions (Crash-resistant Fuel System)p. 118

Fig. 2-3 Engine Access Doorsp. 125

Fig. 2-4 Engine Access Doors (Series 3 Aircraft)p. 126

Fig. 2-5 Engine Access Doors for Aircraft with Upward Exhaustsp. 127

Fig. 2-6 Pilot and Cargo Doorsp. 130

Fig. 2-7 Door Locking Devicesp. 131

Fig. 2-8 Pilot and Cargo Door Detailsp. 133

Fig. 2-9 Pilot and Cargo Door Jettison Mechanismp. 135

Fig. 2-10 Sound Insulation Blanketsp. 139

Fig. 2-11 Seats and Seat Armorp. 142

Fig. 2-12 Repair Limits for Troop Seat Bracketsp. 146

Fig. 2-13 Seat Belt, Shoulder Harness, and Crash Padsp. 147

Fig. 2-14 Inertia Reel and Manual Controlp. 149

Fig. 2-15 Canopy and Window Serviceability Criteriap. 154

Fig. 2-16 Canopy Installationp. 155

Fig. 2-17 Aft Compartment Window Installationp. 157

Fig. 2-18 Typical Laminated Fiberglass Repairp. 161

Fig. 2-19 Body Group Sectionsp. 163

Fig. 2-20 Body Group major Structural Sectionsp. 164

Fig. 2-21 Station Diagramp. 166

Fig. 2-22 Support of Disassembled Aircraftp. 167

Fig. 2-23 Skin Plating Diagramp. 168

Table 2-1 Highly-Stressed Structural Fittingsp. 169

Fig. 2-24 Body Group Fittingsp. 170

Fig. 2-25 Center Beam Repairp. 176

Table 2-2 Premaintenance Requirements for Removal and Installation of Landing Gear Bearingsp. 178

Fig. 2-26 Center Beam Fitting Bearing Replacementp. 179

Fig. 2-27 Landing Gear Fitting Temporary Repairp. 180

Fig. 2-28 NCR Fuel Cell Support Skin Installationp. 181

Fig. 2-29 CR Fuel Cell Support Installationp. 182

Fig. 2-30 Firewall Installationp. 186

Fig. 2-31 Typical Aft Section Firewell Repairp. 187

Fig. 2-32 Typical Engine Compartment Rib Repairp. 188

Fig. 2-33 Station 124.00 Canted Frame Patch Repair (1 of 2)p. 190

Fig. 2-33 Station 124.00 Canted Frame Patch Repair (2 of 2)p. 191

Fig. 2-34 Aft Bulkhead Channel Repairsp. 192

Fig. 2-35 Tail Rotor Drive Shaft Fairing Repair and Replacementp. 193

Fig. 2-36 Position Light Support Repairp. 195

Fig. 2-37 Mast Support Structurep. 196

Fig. 2-38 Boom Fairing Repairsp. 198

Section II – Empennagep. 200

Table 2-3 Structural Repair Materialsp. 201

Table 2-4 Standard Stock Structural Repair Materialsp. 202

Fig. 2-39 Extruded Angle, Equal Leg, Aluminum Alloyp. 203

Fig. 2-40 Extruded Angle, Unequal Leg, Aluminum Alloyp. 204

Fig. 2-41 Extruded Tee, Aluminum Alloyp. 205

Fig. 2-42 Extruded Tee, Bulb, Aluminum Alloyp. 205

Fig. 2-43 Extrusion, Aluminum Alloyp. 206

Fig. 2-44 Extruded Tee, Bulb, Aluminum Alloyp. 206

Fig. 2-45 Extruded Open Angel, Aluminum Alloyp. 207

Fig. 2-46 Tee, Bulb, Unequal Thicknessp. 208

Fig. 2-47 Extrusion, Aluminum Alloyp. 208

Fig. 2-48 Extruded Open Angle, Unequal Legs and Thicknessp. 209

Fig. 2-49 Extrusion, Aluminum Alloyp. 210

Fig. 2-50 Tee, Bulb, Equal Thicknessp. 210

Fig. 2-51 Extrusion, Magnesiump. 211

Fig. 2-52 Extrusion, Aluminum Alloyp. 212

Fig. 2-53 Extrusion, Tee, Unequal Legs, Aluminum Alloyp. 212

Fig. 2-54 Extrusion, Unequal Legsp. 213

Fig. 2-55 Extruded Open Angle, Equal Thickness Legsp. 214

Fig. 2-56 Extruded Tee, Unequal Legsp. 214

Fig. 2-57 Extruded Tee, Unequal Legsp. 215

Fig. 2-58 Extruded Channelp. 215

Fig. 2-59 Tail Surfaces (Empennage)p. 216

Fig. 2-60 Tailboom Assemblyp. 219

Fig. 2-61 Typical Tailboom Skin Patch Repairp. 220

Fig. 2-62 Tailboom Frame and Gusset Repairp. 221

Fig. 2-63 Tailboom Fittingsp. 223

Fig. 2-64 Wire Strike Protection Systemp. 225

Fig. 2-65 WSPS Parts Replacement (1 of 4)p. 235

Fig. 2-65 WSPS Parts Replacement (2 of 4)p. 236

Fig. 2-65 WSPS Parts Replacement (3 of 4)p. 237

Fig. 2-65 WSPS Parts Replacement (4 of 4)p. 238

Ch. 3 ALIGHTING GEARp. 239

Section I – Skids and Strutsp. 239

Table 3-1 Premaintenance Requirements for Removal of Landing Gearp. 239

Fig. 3-1 Landing Gearp. 240

Fig. 3-2 Landing Gear (Lockbolt-mounted skids) Repair and Replacementp. 241

Fig. 3-3 Landing Gear (Machine bolt-mounted skids) Repair and Replacementp. 242

Table 3-2 Maximum Damage Limits for Landing Gear Componentsp. 244

Table 3-3 Premaintenance Requirements for Removal and Installation of Skidsp. 245

Fig. 3-4 Skid Tube Structural Repairp. 247

Table 3-4 Premaintenance Requirements for Damper Extension Checkp. 248

Table 3-5 Damper Extension Checkp. 248

Fig. 3-5 Landing Gear Damper Inspection Methodsp. 249

Fig. 3-6 Landing Gear Damper (Bladder-type) Reference Markingsp. 250

Table 3-6 Premaintenance Requirements for Damper Removal and Installationp. 250

Fig. 3-6A Locally Fabricated Toolsp. 252

Fig. 3-6B Use of Locally Fabricated Toolsp. 253

Fig. 3-6C Poppet-Type Damper Assembly – Exploded and Section Views (1 of 2)p. 254

Fig. 3-6C Poppet-Type Damper Assembly – Exploded and Section Views (2 of 2)p. 255

Table 3-7 Detailed Inspection After Cleaningp. 258

Table 3-7 Detailed Inspection After Cleaning (cont.)p. 259

Fig. 3-6D Minor Repair – Barrel and Lower Cap Assemblyp. 260

Table 3-8 Part No. 369A6350 Damper Assembly Fluid Levelp. 261

Table 3-9 Part No. 369A6350 Damper Assembly Nitrogen Gas Pressurep. 264

Fig. 3-6E Torque Stripe and Decal/Plate Requirementsp. 266

Fig. 3-7 Landing Gear Fairing – Repair and Replacementp. 267

Ch. 4 POWER PLANTp. 271

Section I – Generalp. 271

Section II – Power Plantp. 271

Table 4-1 Troubleshooting of the Enginep. 272

Table 4-2 Premaintenance Requirements for Removal of the Enginep. 273

Fig. 4-1 Engine Disconnect/Reconnect Points (1 of 2)p. 274

Fig. 4-1 Engine Disconnect/Reconnect Points (2 of 2)p. 277

Fig. 4-2 Engine Accessory Replacement (1 of 2)p. 278

Fig. 4-2 Engine Accessory Replacement (2 of 2)p. 279

Table 4-3 Premaintenance Requirements for Removal of Accessoriesp. 280

Table 4-4 Premaintenance Requirements for Installation of Accessoriesp. 281

Table 4-5 Premaintenance Requirements for Installation of the Enginep. 284

Fig. 4-2A OH-6 Accumulator Double Check Valve Installation (1 of 2)p. 285

Fig. 4-2A OH-6 Accumulator Double Check Valve Installation (2 of 2)p. 286

Fig. 4-3 Engine Mounts and Fittingsp. 290

Table 4-6 Premaintenance Requirements for Removal of Lower Engine Mountsp. 291

Table 4-7 Premaintenance Requirements of Installation of Upper Engine Mountsp. 292

Fig. 4-4 Engine Armor Kit Installationp. 294

Table 4-8 Premaintenance Requirements for Engine-to-Transmission Alignmentp. 296

Fig. 4-5 Engine-to-Transmission Alignment Checkp. 297

Section III – Cooling Systemp. 298

Fig. 4-6 Engine Cooling System Installationp. 299

Section IV – Air Induction Systemp. 300

Fig. 4-7 Air Induction System (1 of 2)p. 301

Fig. 4-7 Air Induction System (2 of 2)p. 302

Fig. 4-8 Rework of Replacement Filter Elements (1 of 2)p. 303

Fig. 4-8 Rework of Replacement Filter Elements (2 of 2)p. 304

Fig. 4-9 Simplified Schematic of Inertial Particle Separator Air Filterp. 305

Fig. 4-10 Cold Weather Heat Tube Installationp. 306

Fig. 4-11 Air Induction System Componentsp. 308

Table 4-9 Premaintenance Requirements for Testing Barrier Filter Pressure Switchp. 310

Table 4-10 Troubleshooting of the Filter Bypass Air Indicator Systemp. 310

Fig. 4-12 Barrier Filter Bypass Air Control Installationp. 312

Fig. 4-13 Inertial Particle Separator Air Filter Assemblyp. 314

Fig. 4-14 Bypass Air Control Installation, Inertial Particle Separator Air Filter (1 of 2)p. 317

Fig. 4-14 Bypass Air Control Installation, Inertial Particle Separator Air Filter (2 of 2)p. 318

Fig. 4-15 Engine Anti-icing Valve Control Cablep. 322

Table 4-11 Troubleshooting of the Anti-icing Control Systemp. 323

Section V – Exhaust Systemp. 324

Fig. 4-16 Exhaust Systemsp. 325

Section VI – Oil Systemp. 327

Table 4-12 Troubleshooting of the Engine Oil Systemp. 328

Table 4-12 Troubleshooting of the Engine Oil System (con't)p. 329

Fig. 4-17 Engine Oil Tank (Unarmored Aircraft)p. 330

Fig. 4-18 Engine Oil Tank (Armored Aircraft)p. 331

Fig. 4-19 Engine Oil Supply System Schematic (Armored Aircraft)p. 332

Table 4-13 Premaintenance Requirements for Removal of Oil Coolerp. 335

Fig. 4-20 Oil Cooler and Duct Assemblyp. 336

Fig. 4-21 Oil Cooler Cleaning Setupp. 337

Table 4-14 Premaintenance Requirements for Installation of Oil Coolerp. 338

Table 4-15 Premaintenance Requirements for Removal of the the Oil Supply System Drain Valve and Check Valvep. 338

Table 4-16 Premaintenance Requirements for Installation of the Oil System Drain Valve and Check Valvep. 339

Fig. 4-22 Oil Cooler Bypass Valve Test Setupp. 340

Fig. 4-23 Engine Oil Pressure Sender and Chip Detectorp. 342

Section VII – Power Controlsp. 343

Fig. 4-24 Engine Power Controls Systemp. 344

Table 4-17 Troubleshooting of the Power Controlsp. 345

Fig. 4-25 Gas Producer Controls Riggingp. 346

Fig. 4-26 Power Turbine Governor Controls Rigging (1 of 2)p. 348

Fig. 4-26 Power Turbine Governor Controls Rigging (2 of 2)p. 349

Fig. 4-27 Gas Producer Control Linkage Disassemblyp. 352

Fig. 4-28 Governor Control Linkage (Fwd of Engine Compartment) Disassemblyp. 354

Fig. 4-29 Governor Control Linkage (Engine Component) Disassemblyp. 355

Fig. 4-30 N2 Trim Actuator Test Hookupp. 357

Section VIII – Ignition Systemp. 358

Table 4-18 Premaintenance Requirements for Maintenance of the Ignition Systemp. 358

Fig. 4-31 Automatic Restart System (1 of 2)p. 359

Fig. 4-31 Automatic Restart System (2 of 2)p. 360

Table 4-19 Troubleshooting of the Engine Automatic Restart Systemp. 362

Section IX – Quick Change Assemblyp. 363

Ch. 5 ROTORSp. 365

Section I – Main Rotor Hub and Bladesp. 365

Section II – Main Rotor Hubp. 365

Fig. 5-1 Main Rotor Hub and Bladesp. 366

Table 5-1 Troubleshooting the Main Rotor Hub and Bladesp. 367

Table 5-2 Premaintenance Requirements for Removal of Main Rotor Hubp. 368

Fig. 5-2 Main Rotor Hub Installationp. 369

Fig. 5-3 Main Rotor Mast Locknut Installationp. 370

Fig. 5-4 Pulling Hub Asembly Off Mastp. 371

Fig. 5-5 Hub Assembly Cross Section (1 of 2)p. 372

Fig. 5-5 Hub Assembly Cross Section (2 of 2)p. 373

Fig. 5-6 Strap Pack Lamination Inspection (1 of 2)p. 375

Fig. 5-6 Strap Pack Lamination Inspection (2 of 2)p. 376

Fig. 5-7 Main Rotor Hub Component Repair (1 of 2)p. 377

Fig. 5-7 Main Rotor Hub Component Repair (2 of 2)p. 378

Fig. 5-8 Droop Stop Repairp. 382

Table 5-3 Premaintenance Requirements for Installation of Main Rotor Headp. 383

Table 5-4 Premaintenance Requirements for Droop Angle Inspectionp. 387

Table 5-5 Premaintenance Requirements for Checking Damper Torquep. 388

Fig. 5-9 Rotor Blade Damper Assemblyp. 389

Table 5-6 Premaintenance Requirements for Damper Adjustment, Phasing and Reassemblyp. 391

Fig. 5-10 Damper Torque and Phasing Adjustmentp. 392

Section III – Main Rotor Bladesp. 393

Fig. 5-11 Main Rotor Blade Assemblyp. 394

Table 5-7 Blade Tracking Summary Procedurep. 395

Table 5-8 Premaintenance Requirements for Tracking Main Rotor Bladesp. 395

Fig. 5-12 Typical Track Conditions and Adjustmentp. 396

Fig. 5-13 Main Rotor Blade Tracking Strobe Installationp. 397

Table 5-9 Premaintenance Requirements for Blade Track Adjustmentp. 398

Fig. 5-14 Blade Tab Angle Adjustmentp. 400

Table 5-9A Premaintenance Requirements for Balancing Main Rotor Hub and Bladesp. 402

Table 5-9B Main Rotor Balancing Hardwarep. 403

Fig. 5-14A Main Rotor Blade Balance Equipment Installationp. 404

Table 5-10 Autorotation Rpm Chartp. 405

Fig. 5-15 Main Rotor Blade Normal Damage and Repair Limits for Scratches, Gouges and Nicksp. 406

Fig. 5-16 Main Rotor Blade Normal Damage and Repair Limits for Dents and Depressionsp. 408

Fig. 5-16A Inspection and Repair Main Rotor Blade Metal Abrasion Stipp. 409

Fig. 5-17 Main Rotor Blade Restricted Service Damage and Repair Limits (1 of 2)p. 412

Fig. 5-17 Main Rotor Blade Restricted Service Damage and Repair Limits (2 of 2)p. 413

Table 5-11 Premaintenance Requirements for Main Rotor Blade Repairp. 414

Fig. 5-18 Restricted Service Life Blade Repairp. 416

Fig. 5-19 Vibration Absorberp. 420

Section IV – Main Rotor Controlsp. 421

Section V – Tail Rotor and Control Systemp. 421

Table 5-13 Premaintenance Requirements for Removal of Tail Rotor Assemblyp. 421

Fig. 5-20 Tail Rotor Installationp. 423

Fig. 5-21 Tail Rotor and Pitch Control Assembliesp. 424

Table 5-12 Troubleshooting the Tail Rotor and Control Systemp. 425

Fig. 5-21A Metal Tail Rotor Blade Damage and Repair Areasp. 429

Fig. 5-22 Tail Rotor Pitch Control Assembly Inspectionp. 430

Table 5-14A Premaintenance Requirements for Repair of Metal Tail Rotor Bladesp. 431

Table 5-14B Premaintenance Requirements for Metal Tail Rotor Blade Replacementp. 431

Fig. 5-23A Metal Tail Rotor Blade Replacementp. 433

Table 5-15 Premaintenance Requirements for Installation of Tail Rotor Assemblyp. 434

Table 5-18 Metal Blade Tail Rotor Balance Weight Value Chartp. 437

Ch. 6 DRIVE TRAIN SYSTEMp. 438

Section I – Generalp. 438

Section II – Main Drive Shaftp. 438

Fig. 6-1 Power Train Systemp. 439

Table 6-1 Troubleshooting of the Power Train Systemp. 440

Table 6-1 Troubleshooting of the Power Train System (con't)p. 441

Table 6-1 Troubleshooting of the Power Train System (con't)p. 442

Table 6-2 Premaintenance Requirements for Installation of the Main Rotor Drive Shaftp. 443

Fig. 6-2 Main Transmission Installationp. 444

Fig. 6-3 Main Rotor Drive Shaftp. 445

Fig. 6-4 Main Transmission Drive Shaft and Oil Cooler Blower Replacementp. 446

Fig. 6-5 Overrunning Clutch Repair or Replacementp. 448

Section III – Clutchesp. 450

Fig. 6-6 Overrunning Clutch Oil Level Checkp. 451

Section IV – Main Transmissionp. 455

Fig. 6-7 Main Transmission and/or Lube Replacementp. 456

Fig. 6-8 Main Transmission Cross-Section Viewsp. 458

Fig. 6-9 Transmission Lubrication Pump Oil Filterp. 460

Fig. 6-10 Main Transmission Drain Tubing Installationp. 463

Fig. 6-11 Main Rotor Mast Installationp. 465

Fig. 6-12 Main Rotor Mast Inspection and Repair Criteriap. 466

Section V – Tail Rotor Drive Shaftp. 467

Fig. 6-13 Tail Rotor Drive Shaft, Demper and Tail Rotor (Transmission) Gearboxp. 468

Fig. 6-13A Work Aid, Tail Rotor Driveshaftp. 471

Fig. 6-13B Work Aid, Tail Rotor Driveshaftp. 471

Fig. 6-14 Tail Rotor Drive Shaft Damper Friction Check and Adjustmentp. 473

Section VI – Intermediate Gear Boxp. 474

Section VII – Tail Rotor Gear Boxp. 474

Fig. 6-15 Tail Rotor Transmission Repairsp. 476

Ch. 7 HYDRAULIC AND PNEUMATIC SYSTEMSp. 480

Ch. 8 INSTRUMENTSp. 481

Section I – Introductionp. 481

Section II – Engine Instrumentsp. 481

Table 8-1 Premaintenance Requirements for Maintenance of Tachometer Indicating Systemp. 482

Fig. 8-1 Instruments – Panel Mounted (Typical)p. 483

Fig. 8-2 Tachometer Generatorsp. 484

Fig. 8-3 Tachometer Generator Test Setup (Typical)p. 485

Table 8-2 Troubleshooting the N1, N2 and Rotor Tachometer Indicating Systemsp. 486

Table 8-3 Premaintenance Requirements for Adjusting the Turbine Outlet Temperature Indicatorp. 486

Table 8-4 Troubleshootine the Turbine Outlet Temperature Indicating Systemp. 487

Table 8-5 Premaintenance Requirements for Adjusting the Turbine Outlet Temperature Indicator Harness Resistancep. 488

Table 8-6 Troubleshooting the Engine Torque Indicating Systemp. 489

Fig. 8-4 Engine Torque Indicating System Plumbingp. 491

Table 8-7 Troubleshooting the Instrument Cluster (Engine Oil Temperature and Engine Oil Pressure)p. 493

Section III – Flight Instrumentsp. 493

Table 8-8 Premaintenance Requirements for Troubshooting of Heated Pitot Tubep. 493

Fig. 8-5 Pitot-Static Systemp. 495

Table 8-10 Troubleshooting the Pitot-Tube Heating Circuitp. 497

Table 8-11Troubleshooting the Altimeter and the Airspeed Indicatorp. 501

Table 8-11A Airspeed Indicator Tolerancep. 502

Table 8-11B Altimeter Scale Error Tolerancep. 503

Table 8-12 Premaintenance Requirements for Troubleshooting Attitude Gyro and Ball Bank Indicatorp. 504

Fig. 8-5A Connection for Pitot Leak Checkp. 505

Fig. 8-5B Connections for Static Leak Checkp. 506

Section IV – Navigation Instrumentsp. 507

Section V – Miscellaneous Instrumentsp. 507

Fig. 8-6 Outside Air Temperature Thermometerp. 509

Section VI – Panelsp. 509

Ch. 9 ELECTRICAL SYSTEMSp. 510

Section I – General Informationp. 510

Fig. 9-1 Rectangular Connector Repair and Replacementp. 512

Fig. 9-2 Terminal Block Identification and Replacementp. 513

Fig. 9-3 Terminal Block Locationsp. 514

Section II – Direct Current Power Distribution Systemp. 515

Table 9-1 Troubleshooting the Direct-Current Power Distribution Systemp. 516

Table 9-1 Troubleshooting the Direct-Current Power Distribution System (con't)p. 517

Table 9-1 Troubleshooting the Direct-Current Power Distribution System (con't)p. 518

Fig. 9-4 External Power Receptaclep. 518

Fig. 9-5 Battery Replacementp. 519

Fig. 9-6 Starter-Generator Replacementp. 522

Fig. 9-7 Starter Generator Brush Wear Limitsp. 524

Table 9-2 Premaintenance Requirements for Testing of Starter-Generatorp. 524

Fig. 9-8 Starter-Generator Schematic Diagram and Test Setupp. 525

Table 9-3 Premaintenance Requirements for Adjusting the Voltage Regulatorp. 526

Fig. 9-9 Instrument Panel Electrical Component Replacement (Series 1 and 2 Aircraft)p. 527

Fig. 9-10 Underfloor Electrical Components (Series 3 Aircraft)p. 528

Fig. 9-11 Voltage Regulator Adjustment Provisionsp. 529

Fig. 9-12 Voltage Regulator Test Setupp. 530

Fig. 9-13 Electrical Console Switch Panelp. 532

Fig. 9-14 Relay and Diode Installation – Engine Compartmentp. 533

Fig. 9-15 Circuit Breaker Panel (Series 1 and 2 Aircraft)p. 536

Fig. 9-16 Circuit Breaker Panel (Series 3 Aircraft)p. 537

Fig. 9-17 Electrical Console Light Control Panelp. 540

Table 9-4 Fixed Resistors – Direct-Current Power Distribution Systemp. 542

Section III – Alternating Current Power Distribution Systemp. 542

Section IV – Starting Systemp. 542

Table 9-5 Troubleshooting the Starting Systemp. 543

Section V – Ignition Systemp. 544

Section VI – Lighting Provisionsp. 544

Table 9-6 Troubleshooting the Exterior Lighting Systemp. 545

Fig. 9-18 Anticollision Light and Flasher Replacementp. 548

Fig. 9-19 Position Light Replacementp. 551

Fig. 9-20 Landing/Hover Light Replacementp. 555

Fig. 9-21 Utility Lightp. 556

Table 9-7 Troubleshooting the Interior Lighting Systemp. 557

Table 9-7 Troubleshooting the Interior Lighting System (con't)p. 558

Fig. 9-22 Lamp and Fixture Replacement – Instrument Panelp. 559

Section VII – Caution and Warning Equipmentp. 561

Table 9-8 Troubleshooting the Caution and Warning LIght System (Series 1 & 2 Aircraft)p. 564

Table 9-9 Troubleshooting the Caution and Warning Light System (Series 3 Aircraft)p. 568

Table 9-9 Troubleshooting the Caution and Warning Light System (Series 3 Aircraft) (con't)p. 569

Table 9-10 Troubleshooting Data – Caution and Warning Light System (Series 3 Aircraft)p. 570

Fig. 9-23 Annunciator Panel and Master Caution and Warning Light Panelp. 571

Fig. 9-24 Annunciator Caution Light Assembly (Series 3 Aircraft)p. 572

Section VIII – Miscellaneous Equipmentp. 575

Fig. 9-25 Cyclic Stick Grip (Typical)p. 576

Fig. 9-26 Cyclic Stick Grip Switch-Wiring Diagramp. 577

Fig. 9-27 Collective Pitch Stick Switchesp. 579

Table 9-11 Pilot's Collective Pitch Stick Electrical Wiring – Replacement Datap. 580

Fig. 9-28 Armament Control Panel and Ignition Keylock Switch Locationsp. 581

Fig. 9-29 Armament Central Panel Replacementp. 582

Ch. 10 FUEL SYSTEMp. 584

Section I – Crash-Resistant Fuel Cellsp. 584

Fig. 10-1 CR Fuel Systemp. 586

Fig. 10-2 Folding CR Fuel Cellsp. 589

Table 10-1 Premaintenance Requirements for Pressure Check of CR Fuel Cellsp. 590

Section II – Crash-Resistant Fuel Systemp. 591

Table 10-2 Troubleshooting the CR Fuel Systemp. 593

Fig. 10-3 CR Fuel Cell Access Doorp. 594

Table 10-3 Troubleshooting the Fuel Quantity Indicating Systemp. 595

Fig. 10-4 CR Fuel Quantity Transmitter (Tank Unit 369A4245)p. 596

Table 10-4 Premaintenance Requirements for Testing Tank Unit (369A4245)p. 597

Fig. 10-5 Oil Tank Unit Testing (Transistor Switch Unit)p. 598

Fig. 10-6 CR Fuel Shutoff Valve Control Installationp. 601

Fig. 10-7 CR Fuel Shutoff Valve Installationp. 603

Fig. 10-8 CR Fuel Supply Systemp. 604

Fig. 10-9 CR Crossover Fitting Installationp. 606

Fig. 10-10 CR Vent System Installation (1 of 2)p. 607

Fig. 10-10 CR Vent System Installation (2 of 2)p. 608

Fig. 10-11 CR Closed Circuit Fuel Receiver Installationp. 612

Fig. 10-12 CR Gravity Filter Installationp. 614

Ch. 11 FLIGHT CONTROLSp. 616

Section I – Control Surfacesp. 616

Section II – Flight Controlsp. 616

Table 11-1 Premaintenance Requirements for Rigging Main Rotor Control Systemp. 616

Fig. 11-1 Main Rotor Control Systemp. 617

Table 11-2 Troubleshooting of Cyclic and Collective Controlsp. 619

Table 11-2 Troubleshooting of Cyclic and Collective Controls (con't)p. 620

Fig. 11-2 Main Rotor Control System Rigging (1 of 2)p. 621

Fig. 11-2 Main Rotor Control System Rigging (2 of 2)p. 622

Table 11-3 Isolating Cyclic and Collective Control System Troublesp. 623

Table 11-3 Isolating Cyclic and Collective Control System Troubles (con't)p. 624

Fig. 11-3 Pitch Control Rods and Swashplate Scissors Assemblyp. 625

Fig. 11-4 Main Rotor Swashplate Assemblyp. 629

Table 11-3A Swashplate Bearing Inspection Requirementsp. 634

Table 11-3A Swashplate Bearing Inspection Requirements (con't)p. 635

Fig. 11-5 Mixer Controls Assemblyp. 636

Table 11-4 Premaintenance Requirements for Removal of Collective Pitch Control Rodp. 638

Table 11-5 Mixer Control Component Rework and Wear Limitsp. 639

Fig. 11-6 Tunnel-Routed Control Rodsp. 641

Fig. 11-7 Controls Support Bracket, Idler Bellcranks, and Cyclic Trim Actuatorsp. 642

Fig. 11-8 Controls Support Bracket Critical Inspection Areap. 643

Fig. 11-8A Installation of Collective Stick Support Bracket Reinforcement Strapp. 644

Fig. 11-9 Collective Controls and Bungee Systemp. 647

Fig. 11-10 Pilot's Collective Friction and Throttle Linkagep. 648

Table 11-6 Premaintenance Requirements for Removal of Pilot's Collective Pitch Stickp. 649

Fig. 11-11 Pilot's Collective Stick, Switch, Throttle and Friction Controlsp. 650

Fig. 11-12 Collective Torque Tube, Gas Producer Torque Tube, and Collective Bungeep. 651

Fig. 11-13 Assembly of Pilot's Collective Stick, Gas Producer Linkagep. 652

Fig. 11-14 Adjustment of Gas Producer Drive Mounting Distance and Backlash (Pilot's Collective Stick)p. 654

Fig. 11-15 Adjustment of Collective Pitch Stick Frictionp. 655

Table 11-7 Premaintenance Requirements for Installation of Pilot's Collective Pitch Stickp. 656

Table 11-8 Premaintenance Requirements for Removal of Collective Bungeep. 659

Table 11-9 Premaintenance Requirements for Disassembly of Collective Bungeep. 660

Table 11-10 Premaintenance Requirements for Reassembly and Installation of Collective Bungeep. 660

Fig. 11-16 Assmbly of Copilot's Collective Pitch Stickp. 663

Fig. 11-17 Adjustment of Gas Producer Drive Mounting Distance and Backlash (Copilot's Collective Stick)p. 664

Fig. 11-18 Cyclic Controls and One-Way Lockp. 666

Fig. 11-19 Cyclic Grip and Friction Mechanismp. 668

Fig. 11-20 Cyclic Stick Lateral Control Linkagep. 670

Fig. 11-21 Cyclic Torque Tube and One-Way Lockp. 672

Fig. 11-22 One-Way Lock Installation Adjustmentp. 674

Fig. 11-23 Cyclic Trim Actuator, Test Hookupp. 678

Fig. 11-24 Tail Rotor Control Systemp. 681

Table 11-11 Isolating Tail Rotor Control System Troublesp. 682

Table 11-12 Premaintenance Requirements for Rigging Tail Rotor Control Systemp. 682

Fig. 11-25 Tail Rotor Control System Riggingp. 683

Fig. 11-26 Pilot's Compartment and Intermediate Tail Rotor Controlsp. 685

Fig. 11-27 Upper Fuselage and Boom Tail Rotor Control Linkage (1 of 2)p. 689

Fig. 11-27 Upper Fuselage and Boom Tail Rotor Control Linkage (2 of 2)p. 690

Table 11-13 Tail Rotor Control Component Rework and Wear Limitsp. 690

Ch. 12 UTILITY SYSTEMSp. 694

Ch. 13 ENVIRONMENTAL CONTROL SYSTEMp. 695

Section I – Heating Systemp. 695

Fig. 13-1 Heating Systemp. 696

Fig. 13-2 Heat Control Valve and Distribution Ductsp. 697

Table 13-1 Troubleshooting the Heating Systemp. 698

Fig. 13-3 Heat Control Valve Assemblyp. 701

Section II – Air Cooling Systemsp. 703

Fig. 13-4 Ventilating Systemp. 704

Ch. 14 HOISTS AND WINCHESp. 706

Ch. 15 AUXILIARY POWER PLANTSp. 707

Ch. 16 MISSION EQUIPMENTp. 708

Ch. 17 EMERGENCY EQUIPMENTp. 709

Fig. 17-1 Emergency Equipment Locationsp. 710

Appendix A – Referencesp. 711

Appendix B – Maintenance Allocation Chartp. 715

Appendix C – Aircraft Inventory Master Guidep. 733

Appendix D – Illustrated Field Manufacture Items Listp. 737

Part Number Indexp. 737

Fig. D-1p. 739

Fig. D-2p. 740

Fig. D-3 Part Number 369A4122 Wiring Harnessp. 741

Fig. D-4 Part Number 369A4156 Wiring Harness, Instrumentp. 742

Fig. D-5p. 743

Fig. D-6 Part Number 369A3060 Bracket Assemblyp. 744

Fig. D-7 Part Number 369A4120-3 Receptacle Cap Diskp. 744

Fig. D-8 Part Number 369A4143-15 Harnessp. 745

Fig. D-9 Pin, Headlessp. 745

Fig. D-10 Part Number 369A5370 Plate, IDp. 746

Fig. D-11 Part Number 369A5140 Plate, IDp. 746

Fig. D-12 Part Number 369A5424 Plate, IDp. 747

Fig. D-13 Part Number 369A5369 Plate, IDp. 747

Fig. D-14 Part Number 369A4250-3p. 748

Fig. D-15 Part Number 369A1133 Padp. 748

Fig. D-16 Part Number 369A5430 Plate, IDp. 749

Fig. D-17 Part Number 369A2001-11 Seal, Strut Assemblyp. 750

Fig. D-18 Leaf, Butt Hingep. 750

Fig. D-19p. 751

Fig. D-20 Terminal Boardp. 751

Fig. D-21p. 752

Fig. D-22 Strip, Receptaclep. 752

Fig. D-23p. 753

Fig. D-24p. 754

Fig. D-25p. 755

Fig. D-26p. 755

Fig. D-27p. 756

Fig. D-28p. 757

Fig. D-29p. 757

Fig. D-30p. 758

Appendix E – Storage of Aircraftp. 759

Section I – General Informationp. 759

Section II – Flyable Storagep. 760

Table E-1 Premaintenance Requirements for Flyable Storagep. 760

Table E-2 Premaintenance Requirements for Depreservation after Flyable Storagep. 761

Section III – Premaintenance Requirements for Short Term Storagep. 762

Table E-3 Premaintenance Requirements for Short Term Storagep. 762

Table E-4 Premaintenance Requirements for Depreservation after Short Term Storagep. 764

Table E-5 Premaintenance Requirements for Intermediate Storagep. 765

Table E-6 Premaintenance Requirements for Primary Method of Fuel System Preservationp. 766

Table E-7 Premaintenance Requirements for Alternate Method of Fuel System Preservationp. 767

Table E-8 Premaintenance Requirements for Depreservation after Intermediate Storagep. 769

Section IV – Intermediate Storagep. 765

Appendix F – Wiring Diagrams and Load Chartsp. 771

Wiring Diagram Indexp. 772

Wiring Diagramsp. 800

Fig. FO-1 Series 1 Aircraft Power Supplyp. 800

Fig. FO-2 Series 1 Aircraft Engine Starting and Re-ignition Wiring Diagramp. 801

Fig. FO-3 Series 1 Aircraft Trim Controls Wiring Diagramp. 802

Fig. FO-4 Series 1 Aircraft Instruments and Indicators Wiring Diagramp. 803

Fig. FO-5 Series 1 Aircraft Armament Control System Wiring Diagramp. 804

Fig. FO-6 Series 1 Aircraft Caution and Warning System Wiring Diagramp. 805

Fig. FO-7 Series 1 Aircraft Lighting Systems Wiring Diagramp. 806

Fig. FO-8 Series 1 Aircraft Major Connectors Wiring Diagramp. 807

Fig. FO-9 Series 2 Aircraft Power Supply Wiring Diagramp. 808

Fig. FO-10 Series 2 Aircraft Engine Starting and Re-ignition Wiring Diagramp. 809

Fig. FO-11 Series 2 Aircraft Trim Controls Wiring Diagramp. 810

Fig. FO-12 Series 2 Aircraft Instruments and Indicators Wiring Diagramp. 811

Fig. FO-13 Series 2 Aircraft Armament Control System Wiring Diagramp. 812

Fig. FO-14 Series 2 Aircraft Caution and Warning System Wiring Diagramp. 813

Fig. FO-15 Series 2 Aircraft Lighting Systems Wiring Diagramp. 814

Fig. FO-16 Series 2 Aircraft Major Connectors Wiring Diagramp. 815

Fig. FO-17 Series 3 Aircraft Power Supply Wiring Diagramp. 816

Fig. FO-18 Series 3 Aircraft Engine Starting and Re-ignition Wiring Diagramp. 817

Fig. FO-19 Series 3 Aircraft Trim Controls Wiring Diagramp. 818

Fig. FO-20 Series 3 Aircraft instruments and Indicators Wiring Diagramp. 819

Fig. FO-21 Series 3 Aircraft Armament Control System Wiring Diagramp. 820

Fig. FO-22 Series 3 Aircraft Caution and Warning System Wiring Diagramp. 821

Fig. FO-23 Series 3 Aircraft Lighting Systems Wiring Diagramp. 822

Fig. FO-24 Series 3 Aircraft Major Connectors Wiring Diagramp. 823

Fig. FO-25 NVG Position Light Wiring Diagramp. 824

Fig. FO-26 Searchlight Wiring Diagramp. 825

Fig. F-1 Wire Identification and Circuit Designatorsp. 773

Fig. F-2 Electrical Symbolsp. 774

Table F-1 Equipment List (Series 1 and 2 Aircraft)p. 775

Table F-1 Equipment List (Series 1 and 2 Aircraft) (con't)p. 776

Table F-2 Equipment List (Series 3 Aircraft)p. 785

Table F-2 Equipment List (Series 3 Aircraft) (con't)p. 786

Fig. F-3 Electrical Component Locator (Series 1 and 2 Aircraft)p. 795

Fig. F-4 Electrical Component Locator (Series 3 Aircraft)p. 796

Table F-3 Electrical Power Loading Chartp. 797

Table F-3 Electrical Power Loading Chart (con't)p. 798

Indexp. 826

Specialized inspection routines are provided for post-incident troubleshooting, including heavy landing inspections, sudden engine stoppage checks, main rotor overspeed conditions up to and exceeding 540 RPM, tail rotor strikes, and lightning strike magnetic trace verification. Airframe sheet metal technicians benefit from comprehensive skin plating diagrams, alloy callouts (such as 2024-T3, 2024-T42, and unalloyed titanium), rivet spacing standards, non-stressed fiberglass panel repair methods, and optical scratch polishing criteria for the pilot compartment bubble canopy.

Chapters Covered

Preface: General Information, Quality Assurance/Quality Control (QA/QC), Series Identification, Destruction to Prevent Enemy Use, and Support Equipment Provisions
Chapter 1 – Aircraft General: Servicing, Consumable Maintenance Supplies, Handling, Jacking, Mooring, Hoisting, Ground Handling Wheels, Sling Loading, Special Inspections, and Overhaul & Retirement Schedules
Chapter 2 – Airframe: Fuselage Forward, Lower, and Aft Sections; Non-Stressed Access Doors and Covers; Crew & Cargo Doors; Armament Doors; Jettison Assemblies; Pilot Seats & Armor Installations; Canopy & Cabin Transparency Replacement; and Structural Repairs
Chapter 3 – Alighting Gear: Skids, Struts, Hydraulic Dampers, and Landing Gear Fairings
Chapter 4 – Power Plant: Allison Turboshaft Installation, Engine Mounts, Cooling Air Plenum, Air Induction, Exhaust Systems, Oil Tank & Cooler, Power Controls, and Quick Change Assemblies
Chapter 5 – Rotors: Main Rotor Hub, Offset Flapping Hinges, Lead-Lag Dampers, Main Rotor Blades, Swashplate Controls, and Tail Rotor Assembly
Chapter 6 – Drive Train System: Main Drive Shaft, Overrunning Clutch, Main Transmission, Tail Rotor Drive Shaft, and Tail Rotor 90-Degree Gearbox
Chapter 8 – Instruments: Engine Performance Gauges, Flight Instruments, Remote & Standby Compass Systems, Instrument Panels, and Pitot-Static Lines
Chapter 9 – Electrical Systems: DC Power Distribution, AC Inverters, Starter-Generator, Ignition Circuitry, Caution & Warning Panels, and External Lighting
Chapter 10 – Fuel System: Crash-Resistant Fuel Cells, Vent Networks, Sump Drain Valves, Gravity & Closed-Circuit Refueling Systems, and Non-Crash-Resistant Configurations
Chapter 11 – Flight Controls: Cyclic, Collective, Tail Rotor Directional Pedals, Mixing Linkage, Collective Friction Lock, and Rigging Fixtures
Chapter 13 – Environmental Control System: Cockpit Bleed Air Heating and Defogging Systems, Cabin Air Ventilation Ducts, and Outlets
Chapter 17 – Emergency Equipment: Hand Fire Extinguishers, First Aid Provisions, and Emergency Egress
Appendices: References (Appendix A), Maintenance Allocation Chart (Appendix B MAC), Aircraft Inventory Master Guide (Appendix C), Illustrated Manufacture Items (Appendix D), Flyable & Intermediate Storage Standards (Appendix E), and Electrical Wiring Diagrams & Schematic Load Charts (Appendix F)

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Together, these technical divisions provide an exhaustive resource enabling intermediate repair facilities and flight line maintainers to perform everything from routine 25-hour/30-day battery checks and 150-hour transmission fluid changes to complete teardown and replacement of dynamic flight assemblies.

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Working with authentic maintenance procedures ensures airworthiness, operational reliability, and maximum safety for both flight crew and ground personnel. The Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23 gives technicians the exact engineering tolerances, torque limits (such as chip detector tightening torques of 40 to 50 in-lb and self-closing valves at 50 to 60 in-lb), and structural guidelines needed to keep this historic observation helicopter flight-ready.

This manual is supplied as an instant PDF download immediately upon checkout, allowing rapid viewing on laptops, tablets, or shop desktop workstations without shipping wait times. The high-clarity digital pages are fully printable, letting you print specific wiring foldouts, inspection checksheets, or mechanical overhaul diagrams directly for use in the hangar or flight line.

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Hughes OH-6A Cayuse Helicopter Aviation Unit and Intermediate Maintenance Manual TM 55-1520-214-23

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