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Ep 29 – 5G Radio Altimeter Interference

Podcast, Regs | November 26, 2021

What’s The Potential Impact of A Radio Altimeter Failure on Aircraft Systems?

If your radio altimeter failed or started to provide erroneous or conflicting information, which systems in your aircraft could be affected? This could occur in a critical phase of flight as radio altimeters are generally only active below 2,500 feet.

For the airplane I fly, the Radio Altimeter (RA) has the following importance:

  • The Electronic Flight Instrument System (EFIS) control panels supply radio minimums values to the Display Processing Computer, which calculates radio minimums alerts that show on the display units.
  • Each Flight Control Computer (FCC) uses radio altitude from its on-side Radio Altimeter Receiver transmitter unit.
  • Each Flight Control Computer uses RA in the approach control and low-altitude flight calculations.
  • The Autothrottle (A/T) uses Radio Altitude in the Takeoff/Go Around (TO/GA) calculations and A/T flare calculations.
  • The Ground Proximity Warning System (GPWS) uses Radio Altitude in its ground proximity alert and warning logic calculations.
  • The Traffic Collision Avoidance System (TCAS) computer uses RA to set the sensitivity levels for intruder advisory calculations and to determine if an intruder aircraft is on the ground.
  • The Digital Flight Data Acquisition Unit (FDAU) records RA values.
  • The Weather Radar uses RA to turn on or off the Predictive Wind Shear (PWS) function.

There are many systems that are affected by a Radio Altimeter failure; therefore, there are some decisions to be made when an RA fails. Shown below are portions my aircraft’s Radio Altimeter failure checklist:

Why Talk about Radio Altimeters?

Virtually everyone uses a smartphone and, as customers, we would like faster and faster service. 5G will provide that faster service; however, the frequency range that 5G networks use is very close to those used by aircraft radio altimeters.

Transport Canada issued a Civil Aviation Safety Alert (CASA) 2021-08 in June of 2021, which states in part:

“Innovation, Science and Economic Development Canada (ISED) is the spectrum regulator in Canada. ISED will allow 5G networks and technology in the frequency band 3450-3650 MHz following its auction in June 2021. Additionally, ISED… [will also] allow mobile wireless systems to operate in the frequency band 3650-4000 MHz for 2023. The frequency bandwidth allocated to 5G is close to one used by aircraft radio altimeters (4200-4400 MHz).”

5G is already live in 284 cities in the U.S. and over 380 in China. Many countries in Europe are also live. There are over 1,600 cities in 65 countries with 5G today. Canada has 5G in most major cities.

What Are The Risks to Aviation Safety?

The Canadian Radio Technical Commission for Aeronautics (RCTA) produced a report which concluded that there is a likelihood that 5G radio waves will interfere with radio altimeters. That’s quite a statement. The greatest threat is undetected wrong height information given by the radio altimeter to the aircraft systems. Erroneous or no warnings at all could result in a loss of situational awareness of the cockpit crew.

What Can We Do as An Industry to Protect and Prepare Ourselves?

Many countries already have regulations or advisories for Portable Electronic Device (PED) use. As a crew and an operator, make sure these preventative measures are followed. Educating your clients to the rules is crucial. In Canada, the following rules apply:

  • All 5G PEDs in the cabin should be set to airplane mode or off completely.
  • 5G-capable PEDs should not be allowed to connect to a 5G network.
  • If 5G PEDs are stowed in checked luggage, they should be off and protected from accidental activation.
  • If there is an emergency situation onboard and a smartphone is required, then the PED being used should only connect to a 3G or 4G network.
  • If the flight crew encounters a radio altimeter disturbance, the crew must report it to Air Traffic Services as soon as possible.

If you operate internationally, then make sure to research any country-specific 5G mitigation measures.

Canada Plans to Restrict 5G Service around Airports

So, I wrote this podcast a few weeks ago and, since then, there has been an update to this story in Canada. An online aviation news source, AVweb, is reporting that the Canadian government has proposed restrictions on 5G tower construction or exclusion zones near airport runways. To say this is a big deal to the smartphone industry is an understatement. In the U.S., the Federal Communications Commission (FCC) auctioned the 5G frequencies for $81 billion. The stakes are high, but so is the safety of the travelling public. It appears that the governments are listening to the industry. AVweb also reports that the White House in the U.S. is active in this debate and has scheduled high-level meetings to determine the best course of action.

In Canada, Advisory Circular 700-005 states, “the onus for determining if passenger-operated electronic devices will cause interference is placed on the operator of the aircraft, as there are no airworthiness standards for the manufacture of passenger-operated devices, no maintenance standards and no performance standards in relation to their use on an aircraft.”

The FAA states in InFO 13010, “By regulation, an operator needs to determine that PEDs ‘…will not cause interference with the navigation or communication system of the aircraft on which it is to be used’”. content states that it is solely the aircraft operator’s responsibility to determine whether or not passenger-operated electronic devices will interfere with the aircraft systems for each make and model of aircraft, and then report any interferences. Furthermore, the operator’s documentation should explain the various types or classes of technologies that may be encountered by flight and cabin crew, alongside how they relate to company PED policies.

Refer to your Operations Manual to ensure you understand your company’s specific procedures.

Check out Operations Review training for Personal Electronic Device training.

In The News

OK, let’s change gears for a moment. In The News is a segment of the podcast where I talk about other happenings in aviation.

A Wheelchair’s Overheated Lithium Battery Causes El Al to Cancel Flight

Another lithium battery fire has occurred on an airplane, but, thankfully, it happened on the ground. (If you didn’t listen to my previous podcast on lithium battery fires, then check it out here.) This event occurred in Paris on a 737-900 operated by El Al. The aircraft was about to taxi when a cargo compartment fire warning was annunciated. The flight crew asked the cabin crew if there were any indications of a fire, and there were not. The Captain decided to deplane the guests as a precaution. Once everyone was off, the cargo hold was opened and a burnt lithium battery was found disconnected from a wheelchair. The battery was supposed to be disconnected from the powered chair, but the battery is supposed to be carried in the passenger cabin by the owner, according to Dangerous Goods procedures. The timing of the lithium battery overheat was right, as it happened before takeoff and a well-trained and professional crew dealt with the situation.

Thanks for listening, and have a great day!


AVweb. Canada Puts The Brakes On 5G Cellular Networks Around Airports.

SKYbrary. B739, Paris CDG France, 2019.

Transport Canada. Potential Risk of Interference of 5G Signals on Radio Altimeter – Civil Aviation Safety Alert (CASA) No. 2021-08.

Brent Fishlock, Technical Advisor Team Lead,

aviation professional

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