TH-73A Systems Test Prep 1

A comprehensive set of vocabulary flashcards covering TH-73A helicopter systems, performance limits, and emergency equipment based on NATOPS and Systems Exam ELOs.

Maximum gross weight

The maximum gross weight of the TH-73A for flight is $6,283\,lbs$.

Main rotor diameter

The main rotor diameter of the TH-73A is $35.53\,feet$.

Main rotor assembly

An assembly made up of four blades.

TH-73A rotor head

A fully articulated type of rotor head.

PT6B-37A

The specific turboshaft engine design that powers the TH-73A.

Cockpit seats

Two seats that are crash attenuated or stroking.

Instrument panel console

The console where the PFDs, MFDs, and ESIS are located.

Master Warning and Caution Lights

Located outboard of the PFDs; each pilot has their own set.

ESSENTIAL mode

A mode that allows the MFD to mimic a PFD in the event of a PFD failure or malfunction.

Display Units (DU)

Four units that integrate all helicopter data for display via the central display system.

Primary Flight Information area (PFI)

The name for the upper part of the PFD.

Navigation Data (ND)

The name for the lower part of the PFD.

Electronic Standby Instrument System (ESIS)

An instrument located on the forward instrument panel powered by the battery bus that provides Attitude, Heading, Slip, Skid, Altitude, and Airspeed.

Crew Alerting System (CAS)

A system consisting of Warnings, Cautions, and Advisories shown in chronological sequence with the most recent message on top.

Acknowledging Alert Messages

Pilots must press the master reset pushbutton on the left side of either cyclic or the appropriate Push Button Annunciator (PBA).

Forward engine mount

Located on the bottom side of the engine, it contains two parallel rods that connect the AGB section to the airframe.

Engine architecture

Features an annular combustion chamber, single-stage compressor turbine, and single-stage power turbine.

Engine fuel nozzles

Fourteen nozzles used within the combustion section.

Reduction Gearbox (RGB)

Reduces the power turbine speed and transmits power to the main transmission and tail rotor.

Compressor section

Consists of a three-stage axial and single-stage centrifugal compressor.

Centrifugal impeller

A component in the engine that compresses airflow.

Freewheeling unit

Located outside the AGB section, it contains a sprag clutch (inner race, outer race, and sprags) to allow the transmission and rotors to spin independently of the engine during autorotation.

Engine Accessory Gearbox (AGB)

The section of the engine that acts as the engine oil reservoir.

Engine oil pumps

A system consisting of one gear-type pressure pump and four gear-type scavenge pumps.

Engine chip detectors

Two detectors that identify ferrous metal particles within the oil system; they do not contain a burn-off feature.

Starter motor dropout

The starter motor automatically drops out at $43\,\%$ N1.

Starter sequence

When depressed, the starter drives the compressor / gas generator turbine.

Ignition system

Utilizes two ignitors.

ITT abort threshold

A start should be aborted if ITT rapidly accelerates through $870\,^\circ C$.

Ignition failure

Defined by no rise in ITT or N1 within ten seconds of rotating the twist grip to IDLE.

Fuel Control Unit (FCU)

Establishes proper fuel scheduling based on inputs from P3 air, twist grip position, and N2 governor input.

EEC

Electronic Engine Control; the normal engine control mode setting for flight.

Pneumatic fire detector

The type of fire detection system utilized in the TH-73A engine compartment.

ITT source sensing

Generated by eight thermocouples located between the gas generator turbine and the power turbine.

Compressor Stall

A malfunction characterized by fluctuating N1, abnormal ITT, reduction in torque, and popping or loud bangs.

Fuel tank configuration

Consists of one upper cell and two lower cells.

Anti-surge baffle

A component in each fuel cell designed to restrict fuel from shifting during flight.

Upper fuel cell capacity

Contains a total fuel capacity of $538\,pounds$.

Fuel transfer pump

Moves fuel from the forward portion of the No. 2 cell to the aft portion of the No. 1 cell.

X-FER PUMP caution

Illuminates if the transfer pump has failed or the No. 2 cell is empty.

Fuel quantity probes

Five variable capacitance probes located in the upper and lower cells.

FUEL LOW caution

Illuminates at $100\,pounds$ of fuel, representing approximately $10\,minutes$ of flight time at MCP.

Transmission sections

The Accessory Gearbox (AGB), Reduction Gearbox (main case), and Mast and Bell Housing (upper case).

Transmission Reduction Gearbox

A two-stage gearbox that reduces main driveshaft RPM and changes the direction of drive.

Transmission oil reservoir

The upper case (bell housing) serves as the reservoir for the transmission oil system.

Thomas couplings

Comprised of flexible, stacked stainless steel discs on both ends to provide flexibility and maintain driveshaft alignment.

Main driveshaft

Connects the output shaft of the engine reduction gearbox to the input of the main transmission accessory gearbox.

Tail rotor driveshaft

A two-section shaft connecting the engine RGB to the tail rotor gearbox.

Tail rotor gearbox

Provides a $90$-degree change in direction and reduces RPM.

Rotor brake system

Powered by a dedicated reservoir and pump; operated by a lever on the right side of the overhead console connected via cable.

Rotor brake operating limit

Must only be operated below $40\,\%$ Nr.

Main rotor head inertia

The TH-73A features a low-inertia rotor head.

Main rotor motions

Includes lead-lag, flapping, and feathering (pitching).

Swashplate

Converts linear flight control commands into rotational control input for main rotor pitch.

Mixing unit

Receives and integrates all pilot inputs from the cyclic and collective to provide common output to the main servo actuators.

Cyclic inputs

Controls the pitch and roll axes.

Tail rotor design

A semi-rigid flapping design that uses a Delta hinge to counteract dissymmetry of lift.

Anti-torque pedals

Mechanically designed to control the yaw axis and tail rotor thrust.

Hydraulic pump mounting

The hydraulic pumps are mounted to the transmission main case.

Hydraulic filter group shutoff valve

Controlled by the cockpit servo switch.

Main rotor servo actuators

Three tandem servo actuators powered by both the No. 1 and No. 2 hydraulic systems.

Tail rotor servo actuator

Powered specifically by the No. 1 hydraulic system.

Inner loop functions

AFCS functions primarily concerned with rate dampening and stabilization that do not move the flight controls.

Outer loop functions

AFCS functions that maintain parameters (airspeed, heading, altitude) by moving flight controls to adjust trim.

Helipilot computers

The TH-73A has two of these computers for basic stabilization and autopilot functions.

Force Trim Actuators

Utilizes a torsion spring to provide artificial feel as flight controls move from the trimmed position.

SAS mode

Provides rate stabilization and short-term attitude stabilization.

ATT HOLD mode

Provides long-term stabilization to maintain helicopter attitude indefinitely.

Electrical system specs

Includes a $28\,V$ DC system and a $115/26\,V$, $400\,Hz$ single-phase AC system.

DC power sources

Two generators (Primary/Starter and Auxiliary) and one battery.

AC inverters

Two inverters that supply power for SAS actuators and gyros; sensing relays handle load transfer if one fails.

EXT PWR ON advisory

Indicates the helicopter is connected to an external power source (does not necessarily mean power is being received).

External communication suite

Includes two NAV/COM transceivers, two VHF antennas, and two UHF antennas.

BK-UP mode ICS

In this mode, passengers and crew in the back will lose ICS communications.

Alternate static source switch

Provides an alternate source of static pressure to ADC/ADU 2.

AHRS 1 and 2

Provide heading, pitch and roll angles, and angular rates.

TH-73 Navigation suite

Includes Tacan/DME, VOR, ADF, WAAS enabled GPS, and ADS-B IN/OUT.

Heating system

Mixes fresh ambient air with hot engine compressor discharge air.

Air conditioner inop condition

The compressor is inoperative when the auxiliary generator is the primary power source.

CVDR preflight check

Press and hold the TEST button for $5\,seconds$ and verify the green TEST lamp illuminates.

CVDR impact switch

Stops recording if it senses rapid acceleration/deceleration, high G levels, hard landing, or impact.

ELT switch

Normally set to the ARM position; transmits on $121.5$ and $243.0\,MHz$.

LDG/TAXI LIGHTS

Controlled by the pilot-side collective and an overhead panel; the landing light is angled down.

Inlet Barrier Filter (IBF)

Consists of three filters to prevent particles from entering the engine; the bypass door is opened manually by pressing the IBF filter PBA.

Pitot heat requirements

Powered by the $28\,VDC$ bus; shall be turned on any time the aircraft enters visible moisture regardless of temperature.