Primary barometric altitude display

This case study will consider only the functional requirements for providing barometric altitude readings in the upgraded system. Barometric (or pressure) altitude is used to determine Fhght Level and is based on a standard air-pressure datum. As detailed in Chapter 1, altitude is displayed on the pilot and co-pilot Primary Flight Display (PFD) and on the standby flight instrument. We will consider here only those requirements for display of primary barometric altitude display on each PFD. 

Reliability Fault Tree Analysis for loss of primary barometric altitude display (annunciated)... 

Each of these events represents a separate OR branch for loss of primary barometric altitude display. The FTA in Fig. 4.2 is proposed to represent the way these three events contribute to the top-level functional failure condition. Within the scope (see Step 1) of this assessment, each event was developed further by considering the LRUs involved and their data and power inputs, where applicable. 

Event 1 Loss of primary barometric altitude display (annunciated) FDAL B Event 2 Loss of DCU1 and DCU2 FDALB Event 3 Loss of ADC1 and ADC2... 

System FHA ID4.1.1a Loss of Primary Barometric Altitude Display (annunciated) Hazardous Extremely Remote None... 

To have an annunciated (known) loss of barometric altitude from the primary displays, at least one of the following events must have occurred to the architecture of Fig. 1.8 ... 

VDC -Main DC Bus Loss of power 1x10- / flthr A recognised assumption , refer Lloyd and Tye (p76) IFR conditions Minor DCUl or DCU2 will output error flag to primary displays Barometric altitude available off PFDl, NDl and Stdby FI... 

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