Three of every four of the General Electric CF34-3 engines that power 50-seat regional jets will need to be overhauled within the next three years at a total expected cost of more than $1 billion, according to data compiled with Aviation Week Intelligence Network’s MRO Prospector tool.

The CF34-3 powers Bombardier CRJ100 and CRJ200 aircraft, and more than 1,300 of the engines are in service.

The biggest impact will be at U.S.-based SkyWest Airlines, where essentially all of the 284 engines currently listed as in-service are projected to require overhauls within the next three years at an expected cost of nearly $300 million.

Such maintenance costs do not fall solely on regional carriers as their major-airline partners often cover those costs directly or indirectly. That explains why Delta Air Lines—one of SkyWest’s affiliates—is so eager to speed up reduction of the 50-seater fleet operated by its regional airline partners.

It also explains why some friction has developed among U.S. major carriers and their regional airline partners about maintenance payments or fixed-fee adjustments.

Pinnacle Airlines, which operates its CRJ100/200 fleet only for Delta, is approaching overhauls on nearly 75% of its CF34-3 engines at a projected cost of $180 million. Delta subsidiary Comair also faces overhauls on slightly more than 50% of its 50-seaters’ engines at a projected cost of $50 million.

Air Wisconsin Airlines, which operates its CRJ200s for US Airways, is projected to spend $114 million to overhaul 82% of the engines.

Outside of the U.S., Canada-based Jazz Air is approaching overhauls on 75% of its CF34-3 engines at a cost of more than $75 million, and Spain’s Air Nostrum may need to spend more than $62 million to overhaul nearly all of its CRJ200 engines.