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... Airlines operating in the US may have to upgrade their aircraft radio altimeters again at a cost of billions of dollars, to avoid potential interference with cell networks following the Trump administration's decision last year to auction off additional spectrum to bidders.

On Wednesday, the US Federal Aviation Administration (FAA) issued a notice of proposed new regulations. If implemented, these will require all radio altimeters to meet specific minimum performance requirements.

Those requirements are for altimeters to able to withstand interference from wireless signals in neighboring spectrum bands, while continuing to provide accurate altitude readings to both pilots and integrated aircraft safety systems.

And the cost for all this? The FAA estimates the total bill to retrofit aircraft with interference-tolerant altimeters will be $4.49 billion, or $424 million annualized at a 7 percent discount rate over 20 years.

According to the FAA, the blame for this move lies with the Trump administration and its US budget bill signed into law last year that directed the Federal Communications Commission (FCC) to open up more radio frequencies to be auctioned off for commercial use. ...