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After clearing most aircraft radio altimeters in service in the US for use near 5G masts, now the FAA wants to deal with the rest of them.

We haven’t heard of this problem for a while, but it didn’t go away. For several months last year (and before), we saw a slowly-brewing disagreement between the FAA, the FCC (that oversees telecommunications) and US cellphone carriers. The sticking point was 5G and its deployment near and around airports.

5G: FAA Pushes Airlines To Replace Radio Altimeters

Photo: Bene Riobó, CC BY-SA 4.0

We have discussed the issue at length – look for a Mentour NOW video at the end of the article. But the point here is that 5G can potentially interfere with aircraft radio altimeters – something the FAA and everyone else in the industry found unacceptable.

 

Radio Altimeters, 5G and the FAA

Aircraft radio altimeters typically work in the 4.2-4.4 GHz range. The frequencies that US telecom companies (Verizon, AT&T) got in an FCC auction are in the 3.7-3.98 GHz range. But this is higher (and therefore closer to radio altimeter frequencies) than 5G in other countries. The European Union has set standards in the 3.4-3.8 GHz range. South Korea has an even lower maximum, having set a 3.42-3.7 GHz range.

In many countries around the world, the aviation regulators and the telecom stakeholders reached some workable agreements – early. However, in the United States, the FAA and the FCC could not do the same. In January, the FAA started publishing NOTAMs relating to how certain aircraft use their radio altimeters. Rather than being an isolated system, a radio altimeter, along with weight-on-wheels (WOW) sensors, can seriously affect the behaviour of other aircraft systems.

Towards the end of January, we saw that the situation de-escalated. American telecom companies agreed to postpone the activation of 500 5G towers near airports, for some more time. Meanwhile, the FAA progressively cleared the radio altimeters of about 90% of the US fleet, for normal use. But over the whole country, the remaining 10% is not an inconsiderable number.

5G: FAA Pushes Airlines To Replace Radio Altimeters

Photo: Kyle Fritz

 

The Clock Is Still Ticking

With the telecom companies looking on, the FAA wants to engage airline industry stakeholders to solve the issue. The reason 90% of existing radio altimeters are OK for use, is because they incorporate frequency filters, protecting them from interference. The FAA now wants to set “an achievable timeframe” to replace the remaining radio altimeters.

Delta 767-300ER. Photo: Alf van Beem

That January agreement meant that AT&T and Verizon will delay the activation of those 500 5G towers until the 5th of July. US Transport Secretary Pete Buttigieg has stated that the issue “won’t be completely resolved by this summer.” But note that replacing radio altimeters doesn’t necessarily involve certifying new ones.

The FAA appears to suggest that it could be possible to retrofit frequency filters to existing radio altimeters. The agency has been testing devices and holding “daily meetings” with telecoms and others, since January. However, there are few official statements on the matter, as we get closer to July.

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