|Object Name:||Standby Altimeter|
|Year of Manufacture:||1971|
|Location:||Triple Shelf Unit R (indicators) [Main Store]|
Type No. 81-22-22
Ser. No. 074/71
A barometric altimeter consists of a barometric capsule linked to a pointer by a suitable mechanical or electronic system. The pointer moves across the dial in response to changes in barometric pressure. The dial is calibrated in feet x 1000 or (less commonly) in metres.
Barometric altimeters are provided with a pressure setting control and sub-scale so that the altimeter may be calibrated according to the appropriate pressure setting to indicate flight level, altitude above mean sea level, or altitude above ground level. It has been found that the displays of this type altimeters are capable of being mis-read and several accidents have been attributed to this cause. Accordingly, counter drum-pointer altimeters are the the only type currently approved for use in commercial aircraft. In the BAC1-11 this Altimeter is used as a standby instrument.
Also marked: "EBLR.9.80"
This altimeter acts as a standby to the main altimeter in case of failure. The main altimeter relies on aircraft power to work, so can be compromised by electrical issues. The standby altimeter is purely mechanically / pneumatically operated so will survive a power issue.