Pilot: Aviation Altimeter

"Used this app last weekend. Was within +/-40 feet of my Garmin for the 2.5 hours flight. (FAA standard: +/-75 feet)"--- Xploring Alaska, bush pilot.
"Very Impressive. It was pretty much spot on with my indicated altitude. According to the FAA refs, since the reading is within 75 feet of my altimeter, it pretty much IS spot on. This app would make a great emergency backup in case of an altimeter/ pitot-static system failure." --- Brian, private pilot and owner of a Piper Cherokee.
"That's why I was surprised. At 35,000 feet, it was measuring the cabin altitude, which is what a real altimeter would measure inside the plane [...] Tonight it worked just perfect, I recorded it as we were climbing and the cabin altitude as well." --- David, Airbus captain.
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1. Just Like Professional Aviation
It is a real pressure altimeter using the built-in air pressure sensor (barometer) in your iPhone. Pressure altimeters, also used in professional aviation, are among the most accurate types of altimeters. Here is simple way to test out the app--- open it in an elevator to see how fast and accurately it responses!
2. Why a Pressure Altimeter?
A pressure altimeter is incomparable to some apps that determine your altitude by using only ASTER and/or GPS. GPS is not accurate in determining true altitude, which often results in ~100m (~300ft) error; while ASTER is a library of elevation maps of the Earth. It is a map rather than a true altitude-measuring device. Being a map library, ASTER is problematic when you are not on the ground surface of the Earth— for example in an underground cave, inside a high-rise building, on a hot-air balloon…etc.
3. A True Altitude-Measuring Device
It uses your iPhone’s barometer (air pressure sensor) to detect the surrounding air pressure hence determine your altitude. The principle is that the higher the altitude, the lower the air pressure (in other words: the higher the altitude, the thinner the air which makes it hard to breathe; the lower the altitude, the more “abundant the air is”). That’s how air pressure is used to determine altitude.
4. Accurate Like the Real Thing
Since air pressure at the same location with the same altitude varies everyday due to different weather conditions, the variation would cause a small error in altitude reading. It is negligible for leisure users but crucial for pilots (and serious nerds). Therefore, in real airplanes as well as in our app, there is a feature for you to adjust the air pressure compensation. You may find more instructions inside the app.
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*Disclaimer*
This app is only for leisure entertainment purpose. Although it is designed and engineered for best accuracy, this is NOT a FAA certified flying instrument hence it should NEVER be used for flying or other high-risk activities such as skydiving, hang gliding, hot-air-ballooning etc… Always use certified instruments for the high-risk activities, do not use this app as a replacement. Meanwhile, we hope you enjoy the pocket-sized aviation altimeter!