On October 27, 2019, United Airlines put the latest aircraft type in its fleet, the CRJ-550 into service. The new aircraft is a 50-seat variant of CRJ-700 which can normally accommodate around 70 passengers.
Initially, the “premium” regional jet will be used on flights out of Chicago. In the coming weeks, its also expected to be put on routes out of Newark and Washington Dulles.

CRJ-550: Why Put 50 Seats on a 70-Seater
Just like other major airlines in the United States, United Airlines is limited by scope clauses in their contracts with pilots. Those specify the number and capacity of aircraft that the mainline airlines can outsource to their regional partners.
With United having maxed out the numbers of larger (up to 76-seat) aircraft in operation with its regional affiliates and its 50-seaters aging, the airline for an unusual move in the day and age where the use of 50-seat jets is in decline and airlines try to cram as many seats into aircraft as possible.
It decided to fit CRJ-700s with 50 seats in a move that Ankit Gupta, United’s domestic network vice president, described as:
It’s kind of an out-of-the-box project. Your immediate gut reaction is ‘it’s going to be difficult but you say let’s go through and give it a fair shot.’
The airline partnered with the aircraft’s manufacturer, Bombardier, for this project to “develop” the CRJ-550. In other words, to re-certify the CRJ-700 at a lower maximum take-off weight.
At this point, no airline other than United has plans to introduce the type into its fleet.
United Airlines CRJ-550 Cabin & Service
Introducing the aircraft as CRJ-550 also gave United a chance to market the new 50-seat configuration heavily as “the world’s only 50-seat regional aircraft to offer true first-class seating and other premium amenities.”
Compared the CRJ-700, the CRJ-550 first class seats offer 5 extra inches of legroom. The new aircraft are also equipped with luggage cabinets which – in combination with the overhead bins – will largely eliminate the need for having to gate check bags.

One other interesting thing about the CRJ-550 is that flights operated by the type only have one flight attendant onboard. In other words, there is no dedicated flight attendant in the first class.
At the same time, first class passengers will be able to get a variety of drinks and snacks from a self-serve area at the front of the plane.

Routes Served by the CRJ-550
Initially, United will deploy the CRJ-550 on flights between Chicago O’Hare and Allentown, Pennsylvania; Bentonville, Arkansas; Cedar Rapids, Iowa; Cincinnati, Ohio; Columbus, Ohio; Des Moines, Iowa; Grand Rapids, Michigan; Greensboro, North Carolina; Harrisburg, Pennsylvania; Indianapolis, Indiana; Madison, Wisconsin; Oklahoma City, Oklahoma; Richmond, Virginia; St. Louis, Missouri; and Tulsa, Oklahoma.
It gradually plans to roll out the aircraft on other routes out of Chicago as well.
Separately, it will also use the CRJ-550 on flights out of Newark and Washington Dulles.
The destinations out of Newark that are currently scheduled to switch over to the new aircraft in 2020 include Cincinnati and Columbus in Ohio, Greensboro in North Carolina, and Richmond in Virginia.

Summary
While the CRJ-550 is technically a new aircraft type, in practice, it is essentially a CRJ-700 with limited capacity. In fact, none of the CRJ-550s will be factory-fresh – all will be conversions of existing CRJ-700s.
With the scope clauses in effect, it is understandable why United took this “out-of-the-box” move. However, I wonder what the underlying economics behind the “world’s only 50-seat regional aircraft to offer true first-class” marketing ploy are.