United Airlines continues to evaluate its fleet needs and orderbook, following decisions to defer 61 Boeing 737 deliveries and park its Boeing 747 fleet.

“Our fleet review is a work in progress and we will update you later this year,” says Andrew Levy, chief financial officer of the Chicago-based carrier, during a quarterly earnings call today.

His comments did little to quell questions about the future of United’s order for 35 Airbus A350-1000s, as well as the possibility of additional Boeing 777-300ER orders.

The fleet review, which covers United’s narrowbody, widebody and regional fleets, was launched last year following the restructuring of its senior leadership team that August.

The first move was to defer indefinitely 61 of 65 737-700 deliveries and convert them to the Max in November. The remaining four aircraft were converted to the 737-800 due this year.

The conversion and deferral raised questions on how United will fill the gap in its fleet between 76-seat regional jets and 118-seat 737-700s, especially with the former fleet capped at 255 aircraft under the scope clause with its pilots.

However, the pilots accord allows United to add up to 35 more 76-seat regional jets to its feeder fleet if it adds a new narrowbody, including either the Bombardier CSeries or Embraer 190, to its mainline fleet.

Executives have said previously that improved operational reliability and the restructuring the carrier's domestic schedules will allow it to increase utilisation of existing aircraft.

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This month, United announced that it would retire its 20 remaining 747-400s by the fourth quarter, up to a year earlier than planned.

The carrier will “essentially backfill” the 747s with the 14 777-300ERs, two of which are already in its fleet, it expects by the middle of the year, says Levy. System capacity and routes will remain unchanged, despite the six aircraft net reduction.

“Other than the 747 plans, we have no retirement plans for the rest of the [mainline] fleet,” he says but adds that this could change when the fleet review is complete.

In terms of regional aircraft, United is working on what the “optimal number” of up to 50-seat regional jets is for its fleet, says Levy. Its latest fleet plan shows 207 Bombardier CRJ200s, and Embraer ERJ-135s and ERJ-145s by the end of 2017.

Executives have previously outlined plans for a 50-seat regional jet fleet of as few as 100 aircraft by 2019.

United has firm orders for four 737-800s, one 737-900ER, 104 737 Max 8 and 9s, four Boeing 787-9s and 14 787-10s, in addition to the A350 and 777 orders, the Flight Fleets Analyzer shows.