Giusto x info, tratto dal manuale operativo B767:
----------------------------
AIR DATA SYSTEM
General
The air data system consists of a pitot static system (see Pitot Static Schematic), one temperature and two angle of attack probes, two air data computers and electric flight instruments.
Sensed air data is provided to the air data computers. Processed pressure and temperature from each computer provide input signals to certain flight instruments (Electric Mach/Airspeed Indicator, Electric Altimeter) and other using systems (IRS, AFCS, FMC, FDR, EEC, TMC, GPWS, ATC and others). The Captain's instruments use the L ADC and the F/O's instruments use the R ADC. The opposite ADC is available as an alternate source.
Unreliable air data signals cause warning flags to appear on the air data instruments. When a malfunction occurs in instruments with failure monitors warning flags will appear. On some airplanes the IAS/ALT DIFF advisory message appears on EICAS when there is a significant difference between the Captain's and the F/O's air data sources. This message is inhibited at low altitudes or when both pilots have the same air data source selected.
Two test switches on the accessory panel are provided for ground air data computer testing. They are inoperative inflight. For further information on this test, see Supplementary Normal Procedures.
Mach/Airspeed Indicator
Each Mach/Airspeed Indicator displays airspeed, Mach and Vmo from the selected air data computer. The command airspeed bug on each Mach/Airspeed Indicator can be automatically positioned from the FMC CDU or manually from the MCP IAS/MACH selector.
[...]
Standby Airspeed Indicator
A Standby Airspeed Indicator is installed on the center panel. The instrument is connected directly to the R AUX pitot and the alternate static ports.
Altimeter
Each pitot is provided with a Primary (electric) Altimeter that receives altitude signals from the selected air data computer. An Altimeter Altitude Light and an Altitude Alert Light are provided for altitude alerting. [...]
Standby Altimeter
The Standby Altimeter (penumatic) provides standby altitude information. Input for the indicator is from the alternate static ports.