Register

The 5G Brouhaha

We use MSL altitudes in normal flight as read on our pressure altimeters. Radar and Radio Altimeters measure our height above the ground—absolute altitude.
Gemini Sparkle

Key Takeaways:

  • Absolute altimeters (rad alts) directly measure an aircraft's height above the ground, making them critical for many safety-sensitive systems like autoland, enhanced ground proximity warning, and collision avoidance.
  • These altimeters come in two main types—radio (FMCW) and radar (pulsed)—but both perform the essential function of providing accurate height-above-ground data.
  • The primary concern is that older rad alt designs, operating in the 4.2-4.4 GHz C-band, are susceptible to interference and signal overload from the adjacent, powerful 5G cellular transmissions (3.7-3.98 GHz).
  • To resolve this, existing rad alts will likely need to be retrofitted with improved front-end filtering to prevent 5G signals from disrupting their accuracy, as reallocating 5G frequencies is improbable.
See a mistake? Contact us.

Before we dig into this topic, we need to define some terms. Recall your private ground school where they talked about the different types of altitude measurement? Absolute altitude was one, and it’s the actual distance the aircraft is above the ground at any point, as if you stopped midair and extended a tape measure out the window. Once a popular retrofit in piston singles like Bonanzas and Mooneys, these are now typically only found in far more complex aircraft.

There are two techniques used to measure that absolute altitude. One is properly called a radio altimeter and the other is a radar altimeter. (More below.) The terms are often conflated, so we’ll just use the generic term rad alt when talking about the hardware, and abs alt when talking about the measurement they report.

Ready to Sell Your Aircraft?

List your airplane on AircraftForSale.com and reach qualified buyers.

List Your Aircraft
AircraftForSale Logo | FLYING Logo
Pilot in aircraft
Sign-up for newsletters & special offers!

Get the latest stories & special offers delivered directly to your inbox.

SUBSCRIBE