As you approach the aircraft, check for:

1. FOD
2. Puddles from leaks
3. Listing of the mast
4. Ties removed
5. Unsecured panels
6. Smiling Helo (bent cross tube for the skids indicating a hard landing)
7. General condition.

NOSE AND CHIN BUBBLE AREA: *NATOPS has you check the battery compartment before moving on to the cabin area, then come back to the rest of the nose area after the port fuselage.  During the Fam 0 brief, the instructor demonstrated inspecting the whole nose and chin bubble area first.  BE FLEXIBLE TO YOUR ONWING'S PREFERENCES..

A. Check for un-repaired cracks, general condition and cleanliness
B. OAT gauge - condition and security
Located atop the windshield and a 2-3 inch silver cylinder is visible just to the pilot's side of center.
This is a bimetal, free-air temperature indicator that displays temperature reading in Celsius and Fahrenheit (n 2-36).
C. Divider - integrity
Riveted metal strip separating the left/right windscreens
D. Battery compartment - 
  1. Battery counter and circuit breaker - condition and ensure the breaker is in
Located on the back wall of the battery compartment.
  2. Battery vent (air in) and drain (air out) - connected
The two tubes on the top of the battery.
  3. Battery - condition, security and connection
This is a 24-volt, 17-amp hour nickel-cadmium battery the use a potassium hydroxide electrolyte.  There are two sensors located under the battery that connect to the caution panel.  Sensing of a temperature 54?3?C will illuminate the BATTERY TEMP light and temperature 60?3?C will illuminate the BATTERY HOT light.  Lights will extinguish in the event that temp falls below warning level (n 2-22).
  4. Relays - connection and condition
The two identical, oval shaped objects in front of the battery.
The one closest to the battery is the battery relay and the other is the APU relay.  Switching the battery on energizes the BATTERY relay thereby connecting the battery to the DC common bus.  The same logic is applied to a connected APU w/power applied.  Ensure that the battery is off when using an APU (n 2-17, s 8-4).
  5. General-purpose diode - condition
In the front of compartment, on the service deck, there is a small (about 1.5 inches) protruding object.
This is a for polarization protection (maintenance personnel).
E. Battery door - security
F. Louvered ram air ducts - FOD, security
Grills in the nose on either side of the battery access panel
Two push/pull cables on either side of the center console control the ventilation system.  These intakes direct air to a manifold assembly that in turn provides air to the defog system or direct cabin air ventilation.  Unused air is dumped overboard through the vent hoses (n 2-38, s 7-2).
G. Pitot tube - security, obstructions
-Ensure the word "TOP" is in fact on top.
H. APU door - proper closure
Located directly below the battery access panel
I. Ram air drains (one on each side) - condition
These drains protrude from the chin bubble and tubing connecting the drains and the ram air vents is visible through the chin bubble.  These drains provide an outlet for water taken in ram air vents during inclimate weather.  Note the starboard drain tube has an additional connection, this is a condensation drain.
J. Anti-torque pedals - condition and FOD
Since you are looking at these through the chin bubble, I will make a point to note that you are looking for cotterkeys as well.
K. Searchlight - cleanliness, security
Located under the fuselage, just aft of the nose.  The on/off/stow switch controls the searchlight as well as a directional control switch located on the pilot's collective.  The searchlight system is protected by two circuit breakers located on the overhead panel, one for the power and one for the control.
L. Battery vent/drain - for/aft installation, obstructions
Located on the port side of the searchlight.  Remember that vents face fore and drains face aft.  These connect to the top of the battery.
M. Pitot and static drains - security
Located on the starboard side of the searchlight.  Pitot is on the port side and static is on the starboard side (they are labeled).
N. Instrument screen vent - obstructions
Located under fuselage in aft of the searchlight.

A. FOD, General condition of cabin area
B. Switches - off (in the aft position)
C. Circuit breakers - In
Do not forget ENC and TQ on the lower consul.  ENC corresponds to the mode C function of the transponder and TQ is for the digital display on the torquemeter
D. Twist grip - Check and close
Twist the grip to the full open position, stiffly bring back to flight idle to ensure the idle dent prevents securing the engine, then, by pressing the idle release button, fully close the twist grip.
E. Battery on:
1. 24-volts minimum
2. Fuel quantity
76 gallons max for old bravo models (161xxx) and 91 gallons max for all others.  These are maximums, you will be checking for an indication in line with your weight and balance sheet requirements/limitations.
3. Caution lights (T.H.E.R.G.)
The caution panel is powered by the essential No. 2 bus and is protected by the CAUTION LT circuit breaker
a. Transmission oil pressure
b. Hydraulic pressure
c. Engine out
d. Rotor low RPM
e. Generator failure
4. Torquemeter and TOT - overtorque/overtemp
This is ultimately the instructor's responsibility, but it is good to know.  The digital display will read as such: _O_E flashing twice per second followed by the previous Max torque reading and duration in seconds.  Information on the digital displays of the torquemeter and TOT gauge can be found in NATOPS 2-4.
5.  A/F fuel filter caution light - illumination
The A/F fuel filter button is at the 7 o'clock position on top of the fuel filter (inside starboard engine cowling)
F. Battery - Off
G. Fire extinguisher:
This is a 2-pound BCP (bromochloridfluoromethane) fire extinguisher (n 2-40).
a. Security
b. monthly inspection
c. pressure in the green
d. sealed - cotterkey
H. Shoulder harness, lap belts, and inertial locks - Condition and function
Inertial locks are located behind each seat and are activated by a 2g-3g decelerating force.  You are checking the locking of the harnesses and not the locking mechanism itself.
I. Right rudder - Forward position
This exposes the pitch change rod in the tail rotor for later inspection
J. Pilot's door and window - Cleanliness, damage, and proper function of hinges
Ensure the front door is cotterkeyed.
K. Passenger compartment - FOD and leaks
Fluid in the cabin will most likely collect in the "ditch" on the floor directly in front of the rear seats.
There is an access panel behind the starboard passenger’s set that leads to the avionics’ shelf. (you don't have to touch this)
Behind the port passenger’s seat, there is a black screen.  Warm, cabin air is drawn through the screen by the evaporator fan and passes over the evaporator coils where the expanding Freon, absorbing the heat, cools it.  The cool air is then passed back to cabin (through the cooling air vents) and the warm, gaseous Freon is passed on to the compressor where the cooling cycle begins (s 7-3).
L. Shoulder harness and lap belts - Security (i.e. stowed if not being used)
M. First aid kit - Expiration date and security
Located behind the pilot's seat.
N. Crew comm box - Condition and position
Comm 1 and 2 switches on, hot mike off
O. Passenger door - Cleanliness, damage, and proper function of hinges
Note: it is not essential that passenger doors be cotterkeyed.

A. Starboard static port - obstructions and the baffles are not bent
Static air is used for the altimeter, encoding altimeter, airspeed indicator, and vertical speed indicator.  An alternate static vent is located beneath the copilots seat and is selected by pulling the alternate static source knob on the lower left of the instrument panel (n 2-30)
B. UHF and transponder antennas - Condition and security
The UH10-76 UHF antenna is the large, black blade antenna located below the copilot's seat.  The KA-60 transponder antenna is the small, white antenna located below the pilot's seat.
C. Landing gear:
1. Tow ring - retracted position (forward end of each landing skid)
2. Skid tube - general condition and clamped
At least 6 Mormon clamps on skid tube (7 if aft portion of tube is curved upward)
3. Skid tube/cross tube connection joint - rivets
3,2,1 - any three rivets missing, no two rivets in a row missing, no corner rivets missing
4. Ground handling wheels - removed
5. Cross tubes - cracking and signs of stressing (bowing)
6. Metal strap assemblies - Condition, deterioration, rubber bumpers for cracking, and no metal to metal contact
7. Cross tube well - no metal bowing or cracking
D. Fuel cap - Security
Maximum refueling pressure is 40psi (NATOPS change).  Ensure that cap lock is in a position such that the wind could not lift it up
The panel above the fuel cap is the location for the fuel pressure transducer and fuel shut-off valve.  The fuel pressure transducer is positioned between the boost pumps and the shut-off valve and senses boost pump pressure, it then sends a signal to the fuel pressure gauge.  The fuel pressure gauge is protected by a 1/2-amp circuit breaker located on the overhead panel.  The fuel shut-off valve is a motor-operated shut-off valve installed in the main fuel supply line.  The valve is controlled by an ON/OFF switch located in the instrument panel and is protected by a circuit breaker located on overhead panel.  In the event of an electrical failure, the valve will remain in the last position selected before failure (s 3-8).
E. DM N4-4 VOR nav (pull-up bar) antenna - security
F. Drains and vents - obstructions
Vents face forward and drains face aft.  The following six drains and vents are (and can be remembered) as follows:
Helo - Hydraulics
Flyers - Fuel ram air vent
Get - Gang drain
Evil - a/c Evaporator
Chicks - a/c Condenser
Often - Oil cooler
There is an additional drain, the fuel drain, located in the middle of the under fuselage, about where you would expect the fuel blatter to be. The large access just aft of the a/c condenser drain and the oil cooler drain goes to the evaporator blower.  The hot, pressurized Freon from the compressor is sent to the condenser where the blower cools it as it passes through the condenser coils (visible from the condenser air vent on the port fuselage).  The, still pressurized but now cool, Freon is then stored in the receiver dryer until needed.  Now, when the a/c is turned on (and becomes functional) a low pressure is created between the compressor and the evaporator, which in turn opens an expansion valve.  The expansion valve meters the Freon to the evaporator (s 7-4).
G. KA-54 radar-altimeter antennas - security
These are the two, flat, disc shipped antennas located on the bottom of the helo by the condenser and oil cooler drains. If you did not find them, look again.  They look like circular panels.  The front antenna is for transmitting and the aft antenna is for receiving
H. Lower anti-collision light - condition and security

A. Hydraulic fluid level sight gauge - check
This is a round fluid sight window located toward the top of the Hydraulic Power Pack.  The Power Pack is the large finned assembly toward the rear of the compartment.  Fluid level can be determined by visually inspecting a floating "BB".  This will have the appearance of a light reflection on the window and should appear toward the top of the sight gauge. The Power Pack assembly consists of the hydraulic reservoir, pump, pressure regulator and Nr tach-generator mounting pad and is itself mounted to the transmission and driven by the transmission accessory drive shaft.  The Power Pack houses the hydraulic fluid reservoir and the system uses 2.25 pints (about 1 pint in the reservoir) of MIL-H-83282 (alt MIL-H-5606) fluid.  The filler cap is located on top of the Power Pack and can be inspected from the main rotor hub (n 2-22, n 3-4/6).
The Nr tach-generator is driven by the transmission accessory gear shaft and powers the Nr tachometer.  The normal operational range of the Nr turbine is 90% - 107%; 107% maximum.  If the turbine slows to 90??3%, the ROTOR LOW RPM caution light is illuminated.  Since it is a generator, it creates its own power as long as the gear shaft is turning
B. Hydraulic filter - no popped, red warning indicator, security and leaks
The micronic metal filter is located directly to the left of the starboard access panel.  Check the warning indicator by feeling the top of the filter.  If there is contamination, a red warning button extends upward; otherwise you will feel a dimple where the button is recessed.  Remember that there is no bypass for the hydraulic filter.  Hydraulic fluid is fed to the filter by the hydraulic pump (gear-driven, pressure-loaded; located at the base of the power pack) at 600 ? 50psi.
C. Hydraulic low pressure switch - condition, security, and safety wiring
Vertical metal cylinder just forward of filter.  The low-pressure switch monitors system pressure.  If pressure falls below 300psi, a circuit is closed and the HYDRAULIC PRESSURE light illuminates.  The light will self-extinguish if pressure rises above 400psi.
D. Solenoid valve - leakage and safety wiring
The solenoid is located in the center of the compartment on the service deck and is easily identified by multiple fluid lines connecting to it.  This is a spring-loaded, "fail-safe" valve controlled by a ON/OFF toggle switch located on the pedestal and protected by the HYD BOOST circuit breaker in the overhead panel.  Selecting the OFF position on the switch terminates hydraulic boost to the flight controls.  It is a "fail-safe" system because it is spring loaded open and will automatically return to the open position in the event of power loss (or a pulled circuit) even if OFF is selected (s 6-4).
E. Control tube - condition and security
Tubes located above the solenoid, not directly connected to the hydraulics.
F. Hydraulic servo actuators - condition, security and leaks
Forward portions of the compartment - 3 silver tubes, side by side, oriented fore to aft.  The center actuator assembly is for collective control and the others are for cyclic control (n 2-24).

A. Oil cooling air duct - condition
Thick, coil-hose that blocks the view of everything else.
It provides cooling air from the squirrel-cage fan to the transmission oil cooler.  In the top left corner of the access door, you will see a connector for the engine wash system.  This system cleans the compressor blades only.
B. A-shaped pylon support mount - condition and security
Large yellow mounting bracket between the air duct and transmission casing.  After checking general condition, grip it with your hand such that your thumb is on the washer at the top, sound off "Rocking Rotors" and give the A-frame a firm shake.  You are checking that:
1. You do not feel a pinching movement under your thumb.
2. See a visible and independent movement of the main rotor shaft from the fuselage (most obvious while looking toward the main rotor).
3. You observe movement of the transmission spike within the surrounding well.
C. Transmission casing - damage and leakage
The transmission is lubricated by a wet sump system with pressure provided by a self-contained oil pump immersed in the sump.  The pump delivers oil through the system at a rate of 4.5-5.0 GPM and an operational range of 30-50psi; 70psi maximum.  The transmission oil casing has a capacity of 5 qt. and uses MIL-L-23699/EXXON 2380 (If any other MIL-L-23699 is added flight time is limited to 5hrs due to potential bearing failure because other oils tend to create sludge; n 3-4).  It has no system capacity because, with the exception of the freewheeling unit, the oil does not go anywhere..  This system also provides oil to the free wheeling unit via plumbing visible from the port side.  The transmission has a gear reduction of 15.22:1 from the output shaft (394 RPM from 6000 RPM)(n 2-12, s ch 4).
D. Transmission oil level sight gauge - check
For the first flight of the day, oil level should be at or below centerline; oil level shall be above centerline on subsequent flights.
E. Cannon type chip detectors (2) and drain plug -  security and leakage
Located at the bottom of transmission casing at the one o'clock position (should have rubber boots covering them).  One of the chip detectors doubles as a drain plug. (s 4-5)
F. Transmission spike well area - condition
Spike protrudes from the bottom of transmission at the six o'clock position and penetrates the service deck.  The spike actually ends right there and is surrounded by the by the spike well which provides space for the normal movement of the spike.  The well is secured to the service deck by rivets; sheared rivets, warped or loose well plate, or the spike itself being sheared off are indications of excessive transmission movement or a hard landing.
G. Drag link and isolation mount - condition
Square box to the left of the spike-well area.  The box (isolation mount is constructed of layered "elastomer" and metal which will move under the load of the transmission, then return to its original position when the load is removed.  The drag link connects it to the transmission.  Inspect the drag link connection and the surface of the isolation mount for unpainted scratches or gauges created by barbell shaft contact indicating excessive transmission movement or a hard landing (s 4-12).
H. Drive shaft and coupling - condition and slinging grease
Located directly above the isolation mount and goes through the firewall. The drive shaft has flexible couplings at each end and allows for momentary misalignment of the shaft between the engine and the transmission due to transmission movement.  There two types that you might encounter.  The first type, and most common type, is the K-flex coupling that has the appearance of a leaf-spring construction.  The second, an older style that is being phased out, is cylinder with internal coupling construction and gave the shaft the appearance of a barbell (hence the nickname).  This older style used to have zinc-chromate stripes painted on it to indicated an overtemp situation.  Maintenance then went to a sticker-type tape indicating that has small, white circles that would turn black if overheated.  There are still some of these old barbell shafts around and I encourage you to find one so you are familiar with its appearance (maintenance personnel).  Furthermore, there are (4) locknuts (with painted slip marks) just for ward of the coupling (locknuts are positioned 90 degrees from each other requiring you to reach around and feel for those that cannot be seen or by an inspection from the other side).
I. Service deck - puddles of transmission fluid
It is common for water to collect in the spike-well.

A. Air intake duct plugs - Remove as necessary
B. Air intake ducts - FOD/obstructions
C. FOD screen - obstructions
D. Exhaust stack covers - Remove as necessary
E. Exhaust stacks - bluing, signs of overtemp or overstress
 Ensure there is no contact with the engine cowling

A.  Exhaust stacks - bluing, signs of overtemp or overstress
Ensure there is no contact with the engine cowling.  Check the mormon clamp for security and safety wiring
B. Fuel, oil, and ECS lines - condition, security
This is on going.  Make sure that all hoses and lines are in good condition and that they are properly secured at their connection points.
C. Internal oil filter housing - double safety wiring
Large gray assembly between the diffuser scroll and the exhaust stack.  The housing contains the internal oil filter, associated bypass valve and a pressure-regulating valve.  As you look at it, the regulating valve is closest and the filter and bypass are directly behind it (i.e. behind being closer to the port side).  If you cannot see the safety wiring, rub you hand across the top and feel for two distinct wires.
FYI - The main oil pump, mounted within the accessory gearbox, is run by the Ng turbine, therefore, it provides more oil as Ng and its demand increase. The oil is then sent to the regulating valve, which maintains oil pressure between 50psi minimum and 130psi maximum, with a normal operational range of 90psi to 115psi.  This high-pressured oil is needed to balance high axial gear thrust in the torquemeter, which is needed to minimize friction effects and provide and accurate measurement of torque (n 2-5).
D. Diffuser scrolls, air transfer tubes and combustion section - condition
Aside from the obvious dents and cracks that you are looking for, keep an eye out for bluing on the combustion chamber.  This would indicate an overtemp or an internal problem with the combustion chamber (e.g. improper flow of cooling air).  Physically check transfer tubes for security (i.e. clamps) if engine not hot.
E. Engine mounts - security of engine
Placing hand on aft end of combustion section and attempt to rock fore and aft.  Again, if engine not hot.
F. Heat shield drain for fuel - oil leakage and security
Square aluminum plate just below the air transfer tube that separates the main engine from other components directly below.
G. Compressor bleed air control valve - open position
Located to the right of the diffuser scroll.  There should be a visible gap (about 1”).
The bleed air valve is located on the compressor and bleeds 5th stage air during starting, accelerating and low compressor pressure ratio operations via the control valve which is connected by the required plumbing.
H. Fire detection control box - security
The control box is located at the top of the engine compartment at the very front.  It is about the size of a “C” battery and lies on its side port-to-starboard.  If you are unable to locate it, there is a thin wire that encircles the engine compartment that can lead you to it.
The thin wire is filled with argon gas which, when heated, creates a pressure differential.  The pressure then trips a switch in the control box that illuminates the ENG FIRE caution light.  The fire detection system is protected by the FIRE DET circuit breaker and can be test by a press-to-test button located on the caution panel (n 2-34).
I. Air frame fuel filter - security, leakage
Mounted on the forward firewall (right-hand side as you are looking at it).  Press the manual test button and verify the caution light in the cockpit.  Ensure the drain valve switch is in the horizontal position.
The filter assembly consists of a filter bowl, a replaceable filter element, a drain valve, a bypass valve, an impending bypass switch and a manual test button.  All of the components are internally located except the manual test button (on top of the filter at the 7 o’clock position) and the drain valve (directly below the filter)(n 2-14).
J. ECS muffler - safety wiring
Located just to the left of the fuel filter.
K. Ng tach-generator - security, safety wiring of plug
Black cylinder, located at 5 o’clock position on the front of the accessory gearbox, just behind the orange oil lines. The Ng tach-generator is driven by the gas power turbine and powers the Ng tachometer.  The normal operational range of the Ng turbine is 60% - 105%; 105% maximum (at 100%, Ng rotates at 51,989 rpm).  If the turbine slows to 55??3%, the ENG OUT caution light is illuminated.  Since it is a generator, it creates its own power as long as the Ng turbine is turning
L. Chip detector/plugs - condition
1. Accessory gearbox chip detector
Located at the accessory gearbox’s 6 o’clock position.
2. Freewheeling unit chip monitor
The freewheeling unit is mounted to the lower, front portion of the accessory gearbox.  The chip monitor is located on its lower starboard side, in the area behind the ECS line.  This monitor is not connected to the caution light system (hence the lack of wires) and is only inspected if one of the other detectors illuminate a caution light or during routine servicing (n 2-11).
3. Scavenge oil chip detector
Located on the lower, front of the accessory gearbox in the same vicinity as the freewheeling chip monitor.
M. Twist grip throttle linkage - proper seating, security
The linkage runs horizontally from the forward firewall to about mid-engine, where it is connected to vertical control rod, which connects to the FCU.
N. FCU - security, safety wiring
If you found the throttle linkage, you have found the FCU.  Ensure FCU fuel lever stop arm makes contact with minimum speed stop and that the corresponding indicator is between 0-5.  The fuel lever stop arm is located at the 1 o’clock position as you look at the FCU and the indicator is on the face of the FCU.  Both are easily identified if someone moves the twist grip while you are watching.
O. Starter-generator - signs of arcing, security
Large black cylinder located about mid-engine at the engine’s 5 o’clock position. Ensure the (2) Mormon clamps are secure and safety wired.
This is a 30v, 150amp generator, but regulated to 28v, 105amps.  When the starter is energized, a circuit is opened between the regulator and the generator, isolating the generator from the electrical system (n 2-20).
P. Generator air duct - condition, security
Yellow tube connected to the aft end of the starter-generator.  Transfers cooling air from the vent located on the engine access panel.
Q. Service deck - condition, leakage, potting compound
R. A/C compressor - condition, security
Located near the aft firewall, directly below the tail rotor driveshaft.
Though the compressor is connected (through the belt) to the tail rotor driveshaft and therefore constantly turning, it is not functioning unless AIR COND is selected on the environmental control switch panel.  Then the compressor relay closes, completing a circuit through the temperature control relay to the compressor.  An electrical clutch is then engaged, allowing the routing of compressed Freon gas to the condenser(s 7-4).
S. Fire detection element - proper seating in tracks
Routed around the aft area of the engine section directly above the compressor.

A. Engine oil - check level
The oil system has a capacity of 5.5 qt; .5 qt in the system and 5.0 qt in the tank (maintenance personnel) and uses MIL-L-23699/EXXON 2380.  If any other MIL-L-23699 is added, flight time is limited to 5hrs due to potential bearing failure because other oils tend to create sludge.  An overfull reading is an indication of a ruptured seal between the freewheeling system and the engine oil system (this is the only indication)(s 2-15).
B. Cap - replace and double check security
On top of the oil tank, at the 12 o'clock position, there is some plumbing and a large, gray box. The smaller tubing is an oil vent line, the larger tubing is the oil cooler and associated bypass plumbing.  The gray box is the radiator-type oil cooler.  Directly below the cooler is the squirrel cage fan (it is visible from the other side).  If return oil is approximately 160 degrees Fahrenheit (71 Celsius) or above, it is routed through the cooler before entering the oil tank (s 2-17).

A. Tailboom - security
Place finger on seam between aft fuselage and tailboom, rock tailboom and feel for any movement.
Behind the panel just forward of seam is the location of the KMT-112 Flux Valve Transmitter for the HSI and RMI)
B. VHF antenna - security
The DMC70-1A VHF antenna is the spear-type antenna located on the underside of the tailboom.
C. Tail rotor driveshaft cover - security
All DZUS fasteners shall be 45 degrees from vertical except last one, which is vertical (n 7-7).
D. Horizontal stabilizer - condition
Inspect for cracks, dents, loose or missing rivets; tail boom connections not touching stabilizer; no galvonic corrosion; security of  position light and (4) condensation drains free of obstructions.  Do not mistake drains for the (4) maintenance holes.  Note the negative camber to assist with pitch control in forward flight
E. Main rotor tiedown lanyard - remove at IP's discretion
F. Vertical fin - condition
1. Vertical fin bolts (4) - slipmarks
2. Anti-collision light - condition
3. Tail skid and cover hole - condition
The tailskid acts as a warning in the event of a tail-low landing and serves to protect the vertical fin in such cases.  The skid is rated for 200 lb. downward and 400 lb. upward loads.  The cover hole, located at the base of the tailskid, is inspected by looking through the hole.  A bent hole is an indication of an excessive tailskid load.  Not all of the helos have this hole, some simply have a bolt running through where the hole should be.
The vertical fin is a semi-monocoque construction made of aluminum honeycomb and covered with aluminum skin.  The fin is offset 5.5 degrees from the longitudinal axis creating a horizontal lift component to assist in countering main rotor torque during forward flight
G. Tail position light - condition and security
H. Check/inspect port side of tail boom for same criteria as starboard side after completing tail rotor check

A. Tail rotor gearbox fairing - damage and security
B. Tail rotor gearbox oil level, oil cap installation and chip detector - check
Inspect by looking in the portside grill.  The yellow oil cap will be hard to see; look toward the rear and top of compartment.  The oil level sight window is just to the left of the chip detector. The tail rotor gearbox provides a 90-degree change in direction of drive shaft as well as 2.35:1 gear reduction (2554 RPM from 6000 RPM). The magnesium gearbox uses 3/8 pint of oil and is splash lubricated. The gearbox uses the same oil as the engine and transmission and should be 1/8" above centerline. The chip detector also serves as a drain plug (n 2-14).
C. Crosshead retaining nut - position
Located furthest from the tail boom in the tailrotor assembly.  Look for slip mark and at least on full thread extending through nut
D. Crosshead and pitch change links - condition and security
The links are horizontal and dumbbell shaped. They connect the crosshead and the pitch change horns.  They should move freely about their spherical bearings, but there should not be excessive movement.  Inspect nuts, disc-shaped washers and spherical bearings for condition and security
E. Pitch-change shaft - condition
Located between the crosshead and the knurled nut.  This shaft will not be exposed if the right pedal is not pushed full forward.  Inspection is accomplished by scraping your fingernail along the shaft.  If you are able to "snag" your fingernail, ground personnel shall be notified immediately.
F. Knurled nut and balance wheel - security and safety wiring
The knurled nut is safety wired to the balance wheel, which provides "dynamic balance" to the tail rotor (the wheel, not the wiring).
G. Rubber bumper between yoke and static stop - deterioration
Only one is required, but there are usually two present.
H. Output shaft hub nut and safety washer - security
Located in the same area as the rubber bumper. The washer is not easy to see and will require moving the rubber bumper.  Inspect for safety wiring and the washer for (2) bends outward and (1) bend inward about the static stop
I. Check trunnion grease fitting - security and safety wiring
Blue caps located on both sides of the yoke assembly.  Inspect for balance weights and ensure that the nuts are safety wired.  The washers below the nuts are actually the balance weights that provide chord-wise balance for the tail rotor.
J. Check pith change horns and tail rotor creep bolts - security and safety wiring
The creep bolts are located at the root end of each blade.  Ensure condition and safety wiring.
K. Blade retaining nuts and spherical bearings - condition and security
This is the connecting point between the yoke and the blades.  Inspect nuts and bearings for condition and bolt slip mark.  The washers beneath the nuts provide span-wise balance for the tail rotor.
L. Blade condition and end blade weight balance screws - security
The blades are all metal and have a diameter of 5'5".  They are constructed of aluminum honeycomb and covered by a stainless steel skin. Stainless steel doublers (the layered effect) have been added at the root end for strength and a stainless steel strip has been added to the leading end to reduce erosion.  Each end of the blades have ballast stations for mass balancing and additional weights are added, as required, to balance the blade (i.e. blade weight balance screws at the blade tip) at the time manufacturing.  Chord, span and dynamic balance is set at time of assembly.
M. Output shaft - condition
Located between yoke and tailboom.  Scoring and scraping is acceptable, but excessive damage shall be reported immediately.
N. Garloc seal - leakage
Located at base of output shaft, just inside of the gearbox fairing.  It forms the seal between the output shaft and the gearbox.
O. Flapping and trunnion - clearance and binding
The trunnion is located inside of the hub (under the blue caps, see Systems pg. 5-9) and cannot be seen, but you are checking for binding in the flapping axis.  Blade cannot come within 1" of tail boom.

A.  Scavenge oil filter - Security and impending bypass indication
This filter has a 10-micron rating.  Scavenge oil comes in from behind the filter, is filtered, then sent to the oil cooler through the line visible front access panel.
B. Tail rotor driveshaft safety pin - binding
This pin looks like a small knurled nut and is located just aft of the Thomas coupling on the driveshaft.  It should be loose and free to twist.  If not, it is an indication that the tail rotor driveshaft has be overstressed.
C. Check Thomas coupling - shearing wear
Looks like a bunch of washers bolted together.  Ensure there is no excessive gaping between the discs.
D. Oil drain valve - Position
Located just to the left of the filter and below the oil tank.  Ensure it is in the horizontal/closed position
E. Squirrel cage - FOD, condition
Located at the front of the access area.  The fan is driven by the tail rotor driveshaft and provides cooling air to the oil, transmission and hydraulic systems.
F. Oil sight gauge - Check
Visible through screen just forward of the access panel.  Ensure that oil is above the half way mark.

A. Air intake duct plugs - Remove as necessary
B. Air intake ducts - FOD/obstructions
C. FOD screen - obstructions
D. Exhaust stack covers - Remove as necessary
E. Exhaust stacks - bluing, signs of overtemp or overstress

A. Exhaust stacks - bluing, signs of overtemp or overstress
Ensure there is no contact with the engine cowling.  Check the mormon clamp for security and safety wiring
B. Thermocouples - security
Located on top of the turbine section on the right (FYI - the plumbing on the left is engine oil for turbine lubrication and cooling).  There are four bayonet-type thermocouples that sense the temperature between the Ng and Nf turbines.  The readings are averaged and then relayed to the TOT gauge in the cockpit.  This portion of the system does not give any indications to the pilot, rather the diamond J, TOT gauge displays the temp and signals the TOT caution light if 927 degrees Celsius is exceeded or a time/temp situation occurs for the time limited ranges (s 2-8)
C. Fire detection element - proper seating in tracks
D. Fuel manifold plug and igniter plug - security
Located on the very back of the combustion chamber.  The fuel manifold plug is on the starboard side and has an orange fuel line running to it.  The igniter plug is on the port side and silver connection goes directly to the exciter box.
The igniter only operates when the starter is energized and the generator is isolated.
E. Burner drain valve and drain plug - safety wiring
Located at the lowest part of the combustion chamber.  The plug directly aft of the drain valve is an alternate location for the valve when this engine is used in different aircraft (maintenance personnel).
F. Combustion section, air transfer tubes and diffuser scroll - condition and security
Same as starboard side
G. Heat shield drain for fuel - oil leakage and security
Same as starboard side
H. Pc air filter - hexagonal nut facing aft
Filters air before it is passed on to the Nf governor.  Reverse installation is possible with the filter; nut facing aft is the correct way
I. Diffuser vent and stand pipe - security wiring, no oil leakage from top
A 2"-3" protrusion just to the left of center on the diffuser scroll.  This vents air in the event of an overpressure in the diffuser.  Oil leakage will be an indicator that this has happened.
J. Anti-ice lever - forward position
There is a small motor just aft of the lever, which takes about 10-15 seconds to open/close the valve
K. Drive shaft and coupling - condition and slinging grease
Same as starboard side
L. Nf tach-generator - security, safety wiring of plug
Black cylinder, located behind the linear actuator.  Driven by the free power turbine and powers the Nf tachometer.  The normal operational range of the Nf turbine is 97% - 100%; 100% maximum (at 100%, Nf rotates at 33,956 rpm).  Since it is a generator, it creates its own power as long as the Nf turbine is turning
M. Exciter box - condition, security
Located on the front of the accessory gearbox at the 7 o'clock position.  It does the same thing it did in the T-34.
N. Start counter - lock nuts, security
Small (~1.5"x5"), mostly hidden, located under the accessory gearbox.  Numbers can be read from the back of the counter.  This counter is for maintenance and does not effect the helo.
O. Engine driven fuel pump, filter and drain - condition and security
Mounted below the forward end of the tail rotor driveshaft.  The pump is a gear-driven, pressure fed pump that delivers fuel at 700?50psi.
P. Linear actuator (motor), and governor throttle linkage - condition and security
The whole system is for "droop compensating" (s 2-22).  The linear actuator is for fine adjustments and the throttle linkage is for collective pitch change adjustments.
Q. Nf governor - security and safety wiring
Located behind the accessory gearbox at the 9 o'clock position, just above the tailrotor driveshaft..
Varies the air pressure signals to the fuel control unit in order to prevent lag time between Ng and Nf.  The system has no effect unless the twist grip is in the full open position. (s 2-21)
R. Accumulators - cracks
Two identical cylinders connected at a 90-degree angle, just above the governor.
These dampen transient surges of air pressure.
S. Double check valve - safety wiring
Located between the accumulators.
Prevents a reverse flow of air between the accumulators.
T. Tail rotor driveshaft - excess movement
U. Check Thomas coupling - shearing wear
V. A/C compressor - integrity and condition of belt

A. Drive shaft and coupling - condition and slinging grease
Same as starboard side
B. Transmission oil filter - leakage
The large visible portion is the filter housing; Inside of the housing is the filter.  Mounted to the front is the oil filter head, which houses:
1. The oil monitor - hexagonal nut mounted at an angle.  This is a magnetic chip monitor, but is not wired to caution light system.  It is only checked during routine servicing or if the pilots are alerted through the a caution light.
2. Drain valve - drains oil from the filter for maintenance purposes.
3. Temp bulb - transmits oil temp to gauge in cockpit.  Normal operating range is 15 - 110 degrees Celsius; 110 degrees maximum.
4. Filter bypass valve - in case of a clogged filter
5. High temperature switch - exceeding 110 degrees will close the switch, which illuminates the TRANS OIL TEMP caution light (s 4-4).
C. Transmission casing - damage and leakage
Same as starboard side
The T-fitting sends oil forward for a direct, wet-line reading of transmission oil pressure.  There is a low pressure switch connected to this line that illuminates the TRANS OIL PRESS caution light if it senses a pressure of 30 ? 2psi.  The other line enters the freewheeling unit at the back of the accessory gearbox and the oil is returned in the line directly above the T-fitting (s 4-5).  The thin cylinder sticking out about halfway up the transmission casing at the 7 o'clock position is the system's pressure regulating valve.  It is a spring-type valve that bleeds off internal pressure by allowing oil directly back into the sump, bypassing the jets (n 2-12).
D. A-shaped pylon support mount - condition and security
Same as starboard side
E. Oil cooler and fins - condition
Located on top of the transmission at the 6 o'clock position.  The oil cooler receives its oil directly from the filter and its air from the squirrel cage, cooling fan.  It has a thermal bypass, which closes when oil temperatures rise, forcing the oil to be cooled by the radiator-type cooler.  The regulated air then is passed to either transmission jets or the freewheeling unit.

A. Engine oil cooler - condition and free of obstructions
Located at the rear in the aft fairing.
B. Aft fairing and Engine fairing - condition and security
Ensure the air vents, directly in front of the exhaust stacks, secure and free of obstructions.  The aft fairing is onstructed of aluminum honeycomb with a fiberglass skin.  The engine fairing is made of a heavy aluminum allow.
C. Exhaust stacks - Cracks, dents, burned spots, contact with cowling
D. Induction fairing - condition
Constructed of fiberglass for weight saving and to channel air to the engine.
E. Forward fairing - condition
Constructed of aluminum honeycomb with a fiberglass skin.
F. Transmission compartment - FOD, security
1.  Hydraulic fluid filler cap - Security and safety pin properly installed
This is the top of the Power Pack located at the transmission's 11 o'clock position
2. Transmission oil filler cap - Security
Located on to of the transmission at the 1 o'clock position.  Ensure security by physically twisting the cap.
3. Check security of chip detector continuity sensor
Located at the 12 o'clock position on transmission.
4. Cooling air ducts - Security
There is an orange and black tube that is used by the transmission oil cooler.
5. Control rods - Condition and security
Visually inspect the Actuator Control Tubes and their connections to the Main Rotor controls

PORT HYDRAULIC ACCESS AREA:

A. Solenoid valve - leakage and safety wiring
Same as starboard side
B. Hydraulic control servo actuators - Condition, security and leakage
Same as starboard side
C. Control tube actuator assemblies - Condition and Security
Same as starboard side

ROTOR SYSTEM:

A. Collective lever - Condition and security
This is a yoke-type lever that connects the collective control tube to the pivot sleeve.  Verify the word "TOP" is in fact on the top.
B. Swashplates and lower end of pitch change control rods - Condition, security and freedom of movement
The swashplate and support assembly consists of rotating and stationary swashplates, pivot sleeve, swashplate support and drive link.  The drive link is connected to the connected to the mast (via a lever and a spline mounted collar set) at the top and to the rotating swashplate at the bottom.  The rotating swashplate is connected to the stationary swashplate by a set of bearings and bearing cap.  The stationary swashplate is connected to the top of the pivot sleeve, which is of a uniball construction.  The pivot sleeve is mounted to the swashplate support, which in turn is mounted to the transmission (s 5-12).
Cyclic controls tilt the stationary swashplate about the uniball, subsequently tilting the rotating swashplate.  This tilting will cause the blades to change their plane of rotation.
Collective controls lower the front of the collective lever, causing the back to rise, which lifts the whole pivot sleeve. This lifting will cause the pitch angle to increase and vice versa.
Have plane captain raise and lower collective to ensure freedom of movement within the whole system.
C. Drivelink, lever and collar set - Condition and security
These will cause the rotating swashplate to rotate at the same speed as the rotor system.  The drive link is vertical and the lever is horizontal.
D. Collective boot - Condition, safety wiring on bottom and after clamp on top
This is the black, rubber boot at the base of the mast.
E. Mast and Pitch change rods - Condition and security (nicks, cracks, etc)
Ensure proper installation of the pitch change rods by verifying the course threads are on the bottom and fine threads on top.
F. Rotor hub, internal -
1. Static stops (2) - Condition and security.
Mounted to the bottom of the rotor hub
2. Potting compound on the butt end of tension torsion straps.
The yoke is mounted to the mast by a splined trunnion that is held in place by pillow blocks.  The pillow blocks have bearings inside, allowing the blades to flap about trunnion.  The yoke has 2.25 degrees of preconing to relieve bending stress on the yoke, blade grips and the root ends of the rotor blades.
G. Flap restraint kit - proper operation
Designed to prevent excessive flapping at low rotor RPM.  At low RPMs (32-25% Nr), the springs will pull the restraint arms (flyweight design) in which places the restraint (not visible).
H. Mast nut and Locking device - security and at least one tooth meshed Jesus Nut.
I. Pillow blocks and reservoir - damage and leakage
These are the rounded caps toward the top of the yoke.  They have grease gun fittings on top to allow for lubrication of the inner assemblies (e.g. flap bearings).
J. Pitch-change horns - Condition and safety wiring
K. Blade grip assembly and reservoir - for condition, security, leakage and (3) retaining bolts
They have grease gun fittings on the side to allow for lubrication of the inner assemblies (e.g. pitch change bearings).
L. Blade latch bolt - Security
(a.k.a. horizontal latch bolt)
M. Blade retention bolt and nut - Security and Plastic balance weight caps for security
(a.k.a. vertical through bolt)
N. Rotor blades - Condition and integrity
1. Drag plates - Located at root on the trailing edge
These are mounted on the blades at the time manufacturing and are balance
2. Steel bonding doublers - The layering at the root of the blade
3. Trim tabs - One in the middle and one toward the tip
4. General, overall condition
The blades are of a nonsymmetrical droop design composed of an extended aluminum alloy nose block and stainless steel skin over honeycomb filler.  The main rotor blades have a diameter of 33'4" with a 13" chord and weigh approximately 94 pounds each.  Like the tailrotor, stainless steel doublers (the layered effect) have been added at the root end for strength.
O. From hub, turn blades backwards (i.e. clockwise) to the 90/270 position.
Do not force rotation - this is an indication of carbon lock and could damage Nf turbine.  Carbon lock is a buildup of carbon (soot from combustion) in the turbine section.  The carbon causes the turbine rotors to jam.

A. DM N4-4 VOR nav (pull-up bar) antenna - security
B. A/C condenser air vent - FOD, security
Aft of the baggage compartment.
C. Baggage compartment - for security
Ensure that all gear in the compartment is properly stowed before flight.
TH-57C :  Ensure the circuit breaker is not popped.
D. Passenger door - Cleanliness, damage, and proper function of hinges
Same as starboard
P. Co-pilot's door and window - Cleanliness, damage, and proper function of hinges
Same as starboard
E. Landing gear - condition
Same as starboard
F. Cargo hook and release cable - condition, security
G. Vertical landing light - security
H. Static port - obstructions and that baffles are not bent

» Back to the Advanced Gouge list
» Contact the webmaster, Bryan Weatherup

DISCLAIMER: The information provided on this page is to be used only to assist Student Naval, Marine, Coast Guard Aviators and U.S. Air Force Student Pilots. It is by no means meant to replace or supercede the knowledge presented in NATOPS, OPNAV 3710.7T, Flight Training Instructions, FLIPS, or any other official Navy, Marine, Coast Guard or U.S. Air Force publication. Knowledge of these documents is considered paramount to flight safety. Any unauthorized use of the information on this page in an actual flight (without reference to the official publication) is strictly prohibited. Viewing web pages listed above constitutes acceptance of all responsibility for flight safety by you, the user. The author of this page assumes no responsibility for the completeness of these documents or their use in Aviation training.

If you find discrepencies in the information here, please contact me. This is NOT an official Navy web site. All opinions and statements are exclusively those of the authors and do not reflect the views of the Department of Defense, The United States Navy, The United States Marine Corps, The United States Coast Guard or the The United States Air Force.