Mechanical Standby Attitude Reference Indicator (SARI)

[jrsteensen]

Requirements

• TBD

Reference Material

Simpit A10C - Front Dash - Part 23: Standby Attitude Indicator - Design
Simpit A10C - Front Dash - Part 24: Standby Attitude Indicator - Construction
Simpit A10C - Front Dash - Part 25: Standby Attitude Indicator - Operation Tests and Implementation

MIL Specification

MIL-I-81683A - INDICATOR, ATTITUDE REFERENCE, SELF-CONTAINED, 3-INCH, ID-1791/A

-000 Description

2.12.2 Standby Attitude Reference Indicator. The standby attitude reference indicator (SARI) is a self-contained electrically driven gyro-horizon type instrument. The right 115 volts ac bus normally powers it. If this power fails, an inverter operating off the essential 28 volts dc bus automatically powers it. An OFF flag appears if both power sources fail or the gyro is caged. Ideally the indicator should be in the caged and locked condition prior to application of power. If power has been applied with the indicator in the uncaged condition, wait at least 30 seconds after power application before caging. During caging the gyro initially cages to 4° pitch and 0° roll regardless of aircraft attitude. Caging when the aircraft is in a roll attitude greater than 5° cuts out the roll erection system and the gyro does not erect properly. After 3 to 5 minutes, the indicator reads 0° in pitch and 0° in roll. Both readings assume the aircraft is straight and level. Pitch display is limited by mechanical stops at approximately 90° climb and 80° dive. As the aircraft reaches a near vertical orientation, the roll display experiences large rotations. An aircraft wings level attitude in the vertical orientation may result in large errors in either pitch or roll, or both. This is normal, and is not an indication of damage or improper function of the indicator. After completion of vertical maneuvers the indicator most likely requires caging in the normal cruise attitude, to eliminate the errors. Vertical maneuvers with a wing down condition of 7° or more usually do not develop significant gyro errors. A needle and ball are at the bottom of the instrument. A one-needle width turn is 90° per minute.