Latvian carrier Air Baltic has started restoring services with Bombardier CS300s, following a suspension of the fleet for engine checks.
Air Baltic has not given much insight into the nature of the checks relating to the type's Pratt & Whitney PW1500G powerplants.
But it points out that it was a launch customer for the twinjet, and states that it had "envisaged" a need to undertake upgrades to the aircraft as part of the fleet introduction strategy.
"There are certain technical nuances that are characteristic to new equipment that require additional attention and upgrades during the initial stages of exploitation," it says.
"Similarly to all new aircraft their introduction requires additional attention concerning the harmonisation between different manufacturer parts and systems."
All seven CS300s were temporarily grounded on 11 October while the checks were carried out.
Air Baltic adds that it is co-operating with Bombardier and Pratt & Whitney to "ensure the safety" of the CS300s and "perform the necessary upgrades to the aircraft".
It says the aircraft which have been returned to service are in "full order".
Air Baltic adds that operational results from the CS300s have been "very good", with 21% savings in fuel compared with other aircraft in its fleet.