Why wouldn't they? Engines are by far the most expensive and critical parts of an airliner. So airlines issue RFPs to engine makers to extract the best possible

Why wouldn't they? Engines are by far the most expensive and critical parts of an airliner. So airlines issue RFPs to engine makers to extract the best possible price/conditions. The result of these RFPs is usually a matter of public announcement, see for instance the choice of CFM (a joint venture between GE and Safran) to power IndiGo A320NEO: https://www.ft.com/content/d1c20f9e-9119-11e9-aea1-2b1d33ac3271 https://www.ft.com/content/d1c20f9e-9119-11e9-aea1-2b1d33ac3.... The contract is signed directly between the airline and the engine maker. Of course the engines are installed by the OEM (Boeing, Airbus, etc.), as otherwise delivering the plane would be problematic to say the least... EDIT: another, more relevant example: Norwegian ordered 19 Boeing 787-9 in October 2015, and selected Rolls-Royce to power them in February 2016 (https://atwonline.com/engines/norwegian-selects-rolls-royce-engines-787s https://atwonline.com/engines/norwegian-selects-rolls-royce-...)