• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Flight Mechanic

Aircraft Mechanic School Study Supplement for Future Aviation Maintenance Technicians




  • Home
  • AMT Training
    • Basic Aviation Maintenance
    • Airframes
    • Powerplants
  • AMT Schools
  • AMT Books
You are here: Home / Flight Instruments / Pitot-Static Flight Instruments – Altimeter Part Two

Pitot-Static Flight Instruments – Altimeter Part Two

Filed Under: Flight Instruments

Effect of Nonstandard Pressure and Temperature

It is easy to maintain a consistent height above ground if the barometric pressure and temperature remain constant, but this is rarely the case. The pressure temperature can change between takeoff and landing even on a local flight. If these changes are not taken into consideration, flight becomes dangerous.

If altimeters could not be adjusted for nonstandard pressure, a hazardous situation could occur. For example, if an aircraft is flown from a high pressure area to a low pressure area without adjusting the altimeter, a constant altitude will be displayed, but the actual height of the aircraft above the ground would be lower then the indicated altitude. There is an old aviation axiom: “GOING FROM A HIGH TO A LOW, LOOK OUT BELOW.” Conversely, if an aircraft is flown from a low pressure area to a high pressure area without an adjustment of the altimeter, the actual altitude of the aircraft is higher than the indicated altitude. Once in flight, it is important to frequently obtain current altimeter settings en route to ensure terrain and obstruction clearance.

Many altimeters do not have an accurate means of being adjusted for barometric pressures in excess of 31.00 inches of mercury (“Hg). When the altimeter cannot be set to the higher pressure setting, the aircraft actual altitude will be higher than the altimeter indicates. When low barometric pressure conditions occur (below 28.00), flight operations by aircraft unable to set the actual altimeter setting are not recommended.

Adjustments to compensate for nonstandard pressure do not compensate for nonstandard temperature. Since cold air is denser than warm air, when operating in temperatures that are colder than standard, the altitude is lower than the altimeter indication. [Figure 7-3]

Figure 7-3. Effects of nonstandard temperature on an altimeter.
Figure 7-3. Effects of nonstandard temperature on an altimeter.

It is the magnitude of this “difference” that determines the magnitude of the error. It is the difference due to colder temperatures that concerns the pilot. When flying into a cooler air mass while maintaining a constant indicated altitude, true altitude is lower. If terrain or obstacle clearance is a factor in selecting a cruising altitude, particularly in mountainous terrain, remember to anticipate that a colder-than-standard temperature places the aircraft lower than the altimeter indicates. Therefore, a higher indicated altitude may be required to provide adequate terrain clearance. A variation of the memory aid used for pressure can be employed: “FROM HOT TO COLD, LOOK OUT BELOW.” When the air is warmer than standard, the aircraft is higher than the altimeter indicates. Altitude corrections for temperature can be computed on the navigation computer.

Extremely cold temperatures will also affect altimeter indications. Figure 7-4, which was derived from ICAO formulas, indicates how much error can exist when the temperature is extremely cold.

Figure 7-4. Look at the chart using a temperature of –10 °C and the aircraft altitude is 1,000 feet above the airport elevation. The chart shows that the reported current altimeter setting may place the aircraft as much as 100 feet below the altitude indicated by the altimeter.
Figure 7-4. Look at the chart using a temperature of –10 °C and the aircraft altitude is 1,000 feet above the airport elevation. The chart shows that the reported current altimeter setting may place the aircraft as much as 100 feet below the altitude indicated by the altimeter.

Flight Mechanic Recommends

Rod Machado's Private Pilot Handbook -Flight Literacy recommends Rod Machado's products because he takes what is normally dry and tedious and transforms it with his characteristic humor, helping to keep you engaged and to retain the information longer. (see all of Rod Machado's Products).
   

Primary Sidebar

SEARCH FLIGHT MECHANIC

SEARCH FLIGHT MECHANIC

Aircraft Mechanic Training

Basic Aviation Maintenance

Powerplants

Airframes

Popular Posts

Aircraft Mechanic Salary

Aircraft Mechanic Schools

Aircraft Mechanic Requirements

Aircraft Flight Training

Contact Us | Terms of Use | Privacy Policy
Easy Campfire Recipes | Recipe Workbook



Copyright © 2021 Flight-Mechanic.com