Common Aircraft Altimeters and How They Work
To properly maintain and regulate aircraft elevation, altimeters are used to measure aircraft altitude. Constructed to calculate the height, or altimetry, from aircraft to the surface below, there are varying types of altimeters that can be used to achieve this specific reading. Having this in mind, although not all altimeters are used solely for flight, four primary altimeter types are commonly seen amongst aircraft. These include barometric altimeters, radio altimeters, GNSS (GPS, Galileo, etc.), and laser altimeters. Of these four instruments, we will discuss each and their uses below, which are most commonly used today, and why each is practical for different types of aircraft.
Barometric Altimeters
Barometric altimeters calculate altitude by comparing sea level pressure to the atmospheric pressure currently found at the aircraft's position within the sky. Coming in two main displays, a conventional analogue display or electronic display, the component responds to changes in barometric pressure, projecting the reading upon the display unit. This unit consists of a barometric capsule with an affixed pointer which shifts along a dial within the display. Most often calibrated in feet, the display reading reflects the altimeter's response to changes in barometric pressure.
Radio Altimeters
Radio altimeters are capable of providing an aircraft with an immediate altitude reading. In comparison to older models, modern radio altimeters utilize the measurement of change between a transmitted and reflected signal that is sent towards the ground. Meanwhile, previous generations determined altitude by measuring the time it took for a radio signal to reach the ground and be reflected back towards the aircraft.
Global Navigation Satellite Systems
With the main function of altimeters being used to measure altitude, Global Navigation Satellite Systems, or GNSS, calculate an aircraft's height through the use of trilateration between four or more satellites. Through this method, radio signals are periodically sent from an aircraft and received through receiver components within a satellite, depicting it’s last known location within the atmosphere. However, GNSS are not accurate nor reliable, commonly being used alongside a barometric altimeter to improve reliability or in the case of a faulty device or reading.
Laser Altimeter
Unlike the aforementioned altimeters, laser altimeters rely on electromagnetic waves to determine and calculate altitude. These components generate laser pulses that are sent from the aircraft and downwards towards the earth's surface. The time it takes for these signals to be sent and received then determines the aircraft's altitude, as well as the vertical surface structure of the ground.
Common faults
Not always dependable, altimeters have their fair share of drawbacks which can lead to Altimetry System Error (ASE). Common faults occurring amongst these components generally involve inaccurate variations in aircraft altitude brought on by pressure leaks in pilot or static pipes, faulty Air Data Computers, lack of proper RVSM inspection, and more. Only recently have altimeter monitoring requirements become a criteria for all aircraft systems, having been implemented after the discovery of reduced vertical separation minima (RVSM) to mitigate issues associated with ASE.
If your altimeter is potentially giving you an inaccurate reading and needs to be replaced, look no further than NSN Sphere, your trusted supplier of altimeters and various other aircraft parts and components. For ease of mind, we provide qualifying certifications or manufacturing trace documentation for every purchase as applicable. Furthermore, we are the only independent distributor with a strict no-China sourcing pledge, meaning that all of our offered parts come from reliable sources. Due to our quality control and export compliance, we operate with AS9120B, ISO 9001:2015, and FAA AC 00-56B certification and accreditation. If you would like to request a quote for your comparisons, you can submit an RFQ form as provided on our website. Upon receipt, a dedicated account manager will quickly review and respond with a personalized solution to your needs in just 15 minutes or less, 24/7x365.
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