Mountain Aviation (Denver Rocky Mountain) ceased Citation X operations under its Part 135 certificate, according to ch-aviation research. The carrier is a subsidiary of Wheels Up and operates on its behalf.

The four remaining aircraft, averaging 23 years of age - N908UP (msn 750-0144), N938TX (msn 750-0183), N975TX (msn 750-175), and N988TX (msn 750-0203) - were removed from Mountain Aviation's Part 135-certified fleet in November. Of these, N908UP and N938TX have since transitioned to Wheels Up's Part 135 fleet, while N975TX and N988TX are no longer listed under any certified operator.

Between May and September this year, these Citation X jets ceased operations with Mountain Aviation. N908UP and N938TX have been active under the 'WUP' code since November, while N975TX and N988TX remain parked at Statesville.

Following the retirement of the Citation X type, Mountain Aviation's charter fleet now comprises fourteen Citation Jet 3s, two Citation Jet 3+, and one GIV-SP. As of January, Mountain Aviation's Part 135 certificate included fourty-five Citation X jets. Over the year, these were either retired or transferred to Wheels Up, with the first units joining the latter's certified fleet in July.

Recently, Wheels Up announced a fleet modernisation strategy which will see the company phase out older types, including the Citation Excel, Citation Jet 3, Citation X, and Hawker 400XP, in favour of newer models such as the Phenom 300, Phenom 300E, Challenger 300, and Challenger 350.

ch-aviation reached out to Wheels Up regarding future plans for Mountain Aviation's Part 135 certificate and the fleet operated under it. The company stated that no definitive decisions have been made at this time.