These adjusted values are then applied in accordance with the requirements of the applicable operating regulations and operations specifications. On approach, 31.00 inches will remain set. Although visibility is normally the limiting factor on an approach, pilots should be aware that when reaching DH the aircraft will be higher than indicated. Using the example above the aircraft would be approximately 300 feet higher. These restrictions do not apply to authorized Category II and III ILS operations nor do they apply to certificate holders using approved QFE altimetry systems.
Most pressure altimeters are subject to mechanical, elastic, temperature, and installation errors.
Set the current reported altimeter setting on the altimeter setting scale. Altimeter should now read field elevation if you are located on the same reference level used to establish the altimeter setting. Note the variation between the known field elevation and the altimeter indication. If this variation is in the order of plus or minus 75 feet, the accuracy of the altimeter is questionable and the problem should be referred to an appropriately rated repair station for evaluation and possible correction. Once in flight, it is very important to obtain frequently current altimeter settings en route.