L-1011 Flight Instruments: Barometric Altitude Indicator (ALT) (31-8)

The most typically installed Altitude Indicator on the L-1011has two fail flags:

• SSC - the Static Source Correction feature of the Air Data Computer (ADC) altitude computing has failed. When this flag is displayed, the ADC is still providing altitude data, however, the data is uncorrected. 
• OFF - there has been an ADC input failure or loss of power to the instrument.

Pressing the ALT ALTN Switch on the pilots panel (located below the HSI) will provide the opposite side data to be the affected altimeter and vertical speed unless the actual indicator has failed.