Instruments

Basic instruments consist of those instruments that are not related to radio navigation or communication functions, but rather provide information about the basic dynamic state of the aircraft and engine as it moves through the air, i.e. speed, altitude, direction, temperatures, engine states, etc. The basic instruments consist of the following as illustrated below and described further (in no particular order):

Attitude Director Indicator

The Attitude Director Indicator (ADI) is driven electrically and integrates many systems into one display unit. It contains gyroscopic attitude information for pitch, roll and yaw, radio navigational information for localizer and glideslope and flight director (FD) information for pitch and roll commands as well as a relative radar altitude indicator. Descriptions of each function is below, beginning lower left and working clockwise.

The Attitude Test Button is used to test the gyroscopic functionality when powered on. When pressed and operating correctly, the following indications can be observed:

pitch indication will go to 10º
roll indication will show 20º right bank.
localizer and GS indications will center
ATT warning flag will display

The Radar Altimeter Bar is used to indicate the proximity of the ground to the aircraft during final approach and will be active whenever there is a valid ILS signal being received. It is normally out of sight at the bottom of the ADI and when active, will begin coming into view at 200' AGL and rise to meet the aircraft symbol at 0' AGL.

The Go-Around Annunciator will illuminate whenever the Go-Around mode is activated via the button on the left side of the left power lever. See Autopilot Go-Around Operations for more detail regarding Go Arounds.

The Unreliable Flight Director Flag displays whever there is no power or a malfunction in the Flight Director Computer. When the flag is visible while the unit has power, then the pitch and roll FD bars should be regarded as inaccurate.

The Bank Markings show bank angles of 10º, 20º, 30º, 45º and 60º

The Attitude Flag (ATT) will display whenever the gyroscopes are not fully up to speed and aligned properly. The attitude display should be regarded as inaccurate whenever the ATT flag is visible.

The Decision Height Annunciator is activated whenever a decision height is entered into the radar altimeter preselector and you are descending through the preselected altitude.

The Glideslope Deviation Indicator will indicate GS deviation whenever a valid Glideslope signal is being received.

The FD Pitch Bank Bars will move in response to commands from the flight director, and indicate the pitch and bank angles required for the selected autopilot (AP) lateral and roll modes. When the autopilot is active, it will track the flight director bars.

The Localizer Deviation Indicator will indicate Localizer deviations whenever a valid Localizer signal is being received.

The Sideslip Indicator Ball indicates side slip. Go figure.

Horizontal Situation Indicator

The horizontal situation indicator (HSI) is an electrically driven, gyroscopic instrument and like the ADI above, also combines several functionalities into one unit in order to provide a comprehensive presentation of the aircraft's horizontal situation. The HSI integrates with the gyro/Flux-Gate compass system, the radio navigation receivers and the autopilot.

There are two HSIs, one for the pilot and copilot. The pilot side HSI is coupled to navigation receiver 1 (Nav 1) and the copilot HSI is coupled to navigation receiver 2 (Nav 2). Further, the pilot HSI compass card is coupled to a gyro/flux-gate compass system (compass 1) and the copilot HSI is coupled to the gyro/flux-gate compass system 2 (compass 2). You can read more about the flux gate compass system here. Finally, the pilot side HSI interaces with the flight director / autopilot via the HDG bug knob. The copilot side HSI has a heading bug, but for reference only. A description of each element is given below.

The Omni Bearing Selector (OBS) is used in conjunction with a radio navaid. It is used to select a magnetic courseline from the tuned radio navaid, and the lateral deviation from that courseline can be displayed on the Course Deviation Indicator (CDI). The course selected can be read off of the compass rose, but it is also displayed in the upper left hand corner of the HSI in a digial readout labled COURSE. More about the CDI can be found in the section on Navigation

The Navigation Flag is displayed whenever the HSI is unpowered, or a radio navaid is "tuned into" BUT the signal is not reliable for navigation.

The Heading (HDG) Flag is displayed whenever the HSI is unpowered, or the heading shown on the compass rose does not match the magnetic heading of the flux-gate compass, which normally drives the compass card. The HSI compass card can wander when the unit is unpowered and the aircraft is towed, moved, etc. The section on Navigation discusses the flux-gate compass and HSI coupling in more detail.

The Heading Bug is used in conjunction with the Autopilot when it is in Heading (HDG) mode. This bug is adjusted via the Heading Bug Knob on the unit and sets the magnetic heading for the Autopilot to follow.

The Course Deviation Indicator (CDI) is used in conjunction with a radio navaid in general, but can also be used in conjunction with a GPS in some cases. The CDI needled indicates how far off course you are from the magnetic courseline tuned to via the OBS. It also indicates whether the courseline is to your left or right.

The DME Distance (Distance Measuring Equipment) readout is used in conjunction with radio navaids that have DME capability. When DME equipment is installed along with the navaid equipment, then the distance to the navaid, in nautical miles, is displayed in this window.

The Glideslope Deviation Indicator is used in conjunction with glideslope equipment installed on a runway. When your navigation radio is tuned to a glideslope frequency, then this indicator will show your position above or below the glideslope.

The Vertical Guidance flag is displayed whenever the HSI in unpowered, or is receiving a Glideslope signal that is unreliable.

The TO/FROM indicator always points TOWARDS the navaid that is tuned into. The pilot side HSI uses Navigation Receiver #1 (NAV1) and the copilot side HSI uses navigation receiver #2 (NAV2)

Peripheral Instruments

Airspeed Indicator
The airspeed indicator (ASI) indicates the airspeed in Knots. The face is color coded to indicate notable airspeeds and ranges. The upper redline speed is marked at 250 knots, the lower at 99. The normal operating speed range is contained within the green arc (106-250) and the full flap (40º) operating range is shown within the white arc (81-120). The blue line (best single engine rate of climb) is marked at 152. The ASI relies on the pitot-static system and requires no electricity to indicate airspeed, but does have internal lighting.

Radio Magnetic Indicator (RMI)
The RMI is primarily used with navigation radios and those navigation functions are discussed in more detail in the Navigation section; however, like the HSI, the RMI also has a compass card that is coupled to the flux-gate compass system and so provides basic heading information. Whereas the pilot HSI utilizes the flux-gate compass 1 system, the pilot RMI uses the flux-gate compass 2 system. Similarly, the copilot HSI uses compass 2 and copilot RMI, compass 1. This configuration allows for the convenience cross-check of the two flux-gate compass systems, in that they should agree on the heading displayed by all four instruments (2 HSIs, 2 RMIs)

Turn and Slip Indicator
The turn and slip indicator are two instruments in one. The turn indicator is a gyroscope instrument and indicates the rate of turn/heading. When the indicator is fully aligned with a hash marks either side of the center hash mark, then the aircraft is in a 3º per second, 2-minute, standard rate turn. The spacing between the two outer hash marks and the center hash mark is equal in width to the needle, such that when the need is aligned between the hash marks as shown at left, then the aircraft is in a half standard rate turn.

Altimeter
The altimeter is electrically powered and of the encoding type, receiving altitude information from an air data computer (ADC). (The copilot side altimeter operates from the pitot-static system only and serves as a backup. The altitude is displayed with a combination of scrolling digits and dial indication. The dial indication only shows 100s of feet. 1000s of feet, along with 100s also, is indicated in the scrolling digits window. The barometric pressure setting is displayed in both HG and MB and can be adjusted via the BARO knob on the lower left of the unit. An altitude bug is also provided, and adjusted via the knob on the lower right of the unit. The altitude bug is for pilot reference only and is not coupled to any other equipment such as the autopilot. The altimeter contains internal lighting

Vertical Velocity Indicator (VVI)
The VVI operates from the pitot-static system and indicates the vertical velocity of the aircraft. It requires no power for indication, but does utilize power for internal lighting.

Engine Instruments / Markings

TORQUE METERS
The torque meters indicate torque measured between the turbine and propeller. The torque meters indicate 100% torque at the engine's flat-rating of 715 shaft horsepower. Redline is 100%. Yellow markings provide a visual cue of approaching redline and is not an indication of restricted operating range. The torque meters are powered by the AC inverter system and when unpowered, will indicate 100%.

EXHAUST TEMP The exhaust temperature gauges indicate measured EGT, in ºC whenever the engine RPM is below 80%. When the engine is above 80%, the EGT indications are driven by the SRL computer and indicate a compensated EGT which is higher than true EGT. Redline is marked at 650ºc and is valid whenever the SRL computer is ON and functioning. With the SRL OFF, the EGT limits shown on the Outside Temperature Gauge should be observed. The EGT gauges are powered through the DC feeder busses.

FUEL FLOW The fuel flow indicators indicate FF in LBS/HR and are powered through the DC feeder busses.

PERCENT RPM RPM gauges indicate engine RPM, in percent, where 100% represents a propeller speed of 1591 RPMs. Colored arcs indicate notable operating ranges. The yellow and green arcs represent the acceptable RPM ranges usable during ground operation. The green arc represents the usable range for airborne operation. The RPM instruments are powered through the DC feeder busses.

OIL TEMPERATURE The Oil temperature gauges indicate operating oil temperatures and are powered through the DC feeder busses.

OIL PRESSURE The Oil Pressure gauge is a single gauge that indicates for both engines. There are two needles, one behind the other, with one labled L and the other labled R. Colored markings / arcs indicates operating ranges and limits. The Oil pressure gauge is powered through the AC inverter bus.

Fuel Indications

Fuel Indicators consist of a fuel pressure gauge and 3 fuel quantity indicators. The fuel pressure indicator and MAIN fuel quantity indicators are powered through the AC inverter bus while the Outer and Tip fuel quantity indicators are powered through the DC feeder busses. The fuel pressure gauge, like the oil pressure, is a single indicator for both engines, with L and R needles.