Attitude Heading Reference System

STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS

CHAPTER TEN

Indicated Airspeed Displays

The MSI provides two IAS displays, one is digital and one is an IAS pointer rotating around a

scale.

IAS Digital Display - The green numeric display indicates current IAS in one-knot

increments. Green dashes appear when IAS drops below 30 knots. Green dashes are displayed

until the current IAS is greater than 35 knots or when IAS data is not received. An IAS

annunciation appears when IAS data is not valid. The IAS display is red and continuously

flashes and the overspeed warning horn is activated when Maximum Operating Speed

(VMO)/Maximum Mach Operating Speed (MMO) is exceeded.

IAS Pointer and Scale Display - The green IAS pointer indicates current indicated

airspeed and rotates around a 60-420 knot white airspeed scale. A red striped VMO pointer

rotates around the IAS scale indicating maximum operating airspeed for existing flight

conditions. The display blanks and a red pointer icon appears in the IAS pointer when the ADC

VMO data is not valid.

Mach Speed Display

The green numeric display indicates current mach speed. The hundredths digit simulates a

rotating mechanical wheel. The mach speed display and legend is visible when mach speed is

0.45 or greater. The mach speed display is red and continuously flashes and the overspeed

warning horn is activated when VMO/MMO is exceeded.

1. IAS/Mach Reference Display - The reference airspeed display will automatically

transition to the mach reference as the aircraft climbs through 29,500 feet. The IAS/mach

reference display is blanked when the IAS or mach reference is not valid.

2. TAS Display - The green numeric display indicates current true airspeed. Green dashes

are displayed when TAS data is not received. Red dashes are displayed when the TAS data is

invalid.

3. Temperature Display - The green display indicates RAT, SAT, or ISA, calculated from

input data sensed by the dual element temperature probe and calculated by the respective ADC

computers. The normal display is RAT.

1009. ATTITUDE HEADING REFERENCE SYSTEM

The AHRS provides attitude gyro, directional gyro (compass), and accelerometer functions. The

AHRS is a dual system (one for each P). Each system functions independently but can supply

data for both positions by using a reversion function. The AHRS consists of two AHCs, two

Flux Detector Units (FDU), EFIS displays, switches and indicators, and a standby battery. If

primary power to the AHRS drops below a preset limit, the AHC automatically switches to

standby power. The standby power supply provides approximately 11 minutes of AHC

operation. During a failure, flags on the EADI, EHSI, and MFD (if composite) are annunciated.

AVIONICS

10-9