Are there any commonly used passenger aircraft larger than regional jets (100+ seats) that aren't Boeing or Airbus?
If so, what are they and where are they used?
Yes. Ignoring companies that used to exist but are now bankrupt/merged into Airbus or Boeing, you have companies from countries that aren't historically too friendly with the US and Western Europe. For instance, Tupolev makes the Tu-204, which is currently in production and seats over 175 passengers. The Ilyushin-designed Il-96 is a widebody in current use some places (Russia, Cuba). Before the Cold War ended, Russia had more indigenous airliners; Aeroflot now largely uses Boeings and Airbuses, but there are still Russian aircraft that see use.
In addition, you have newer manufacturers starting to enter the market: Bombardier with their CSeries, Comac (in China) with their C919 (in development), and Irkut with their MC-21 (in development). Embraer makes planes of more than 100 seats (although they're shorter-range, and you might consider them regional jets).
Being used but out of production:
Boeing = Historic Boeing, not McDonnell Douglas, or plain Douglas
Airbus = Historic Airbus.
Commonly used= ?
A reputable source would be http://www.airliners.net/aircraft-data/ From there and comments here, I have edited the following list of manufacturers, for a concise answer, and below that, a list of the aircraft which I believe have more than 100 seats, or can be configured with 100 or more seats, and are in revenue service today, 2015:
Antonov An-124 Ruslan Heavylift freighter
Antonov An-140 New! Turboprop regional airliner
Antonov An-225 Mriya Extra-Large cargo aircraft
Bombardier CRJ-1000 (& C-100, C-300, when deliveries start)
BAE Systems Avro RJX100 Regional airliner
British Aerospace Avro RJ85/100 Regional airliner
British Aerospace BAe-146-200 &-300 Regional jet airliner
Douglas DC-7 Piston engine airliner and freighter
Douglas DC-8-60/70 Long range medium capacity airliner and freighter
Embraer ERJ-195 108 seat regional airliner
Fokker 100 100 seat regional jet
Ilyushin Il-18 Medium range turboprop airliner
Ilyushin Il-62 Medium to long range medium capacity airliner
Ilyushin Il-76 Medium to long range freighter
Ilyushin Il-86 Medium range widebody airliner
Ilyushin Il-96-300 Long range widebody airliner
Ilyushin Il-96M & Il-96T Long range widebody airliner and freighter
McDonnell Douglas DC-10 & Boeing MD-10 Medium to long range widebody airliner
McDonnell Douglas DC-9-40/50 Short to medium range airliners
McDonnell Douglas MD-11 Long range widebody airliner
McDonnell Douglas MD-81/82/83/88 Short to medium range airliner
McDonnell Douglas MD-87 Short to medium range airliner
McDonnell Douglas MD-90 Short to medium range airliner
Sukhoi Superjet SSJ-100 Regional jet airliner
Tupolev Tu-154 Medium range airliner
Tupolev Tu-204 & Tu-214 Medium range airliner
Yakovlev Yak-42 Short range airliner
Once common, now mostly or all retired:
Aerospatiale-British Aerospace Concorde Medium range supersonic airliner
Antonov An-22 Antei Large capacity turboprop freighter
Avions Marcel Dassault (AMD) Mercure
BAC 111 One-Eleven -500. Short haul airliner
Canadair CL-44 & Yukon Medium to long range airliner and freighter
Convair 880 and 990
De Havilland Comet Medium range airliner
Douglas DC-6 Piston engined airliner and freighter
Douglas DC-8-10/20/30/40/50 Medium to long range airliner and freighter
Hawker Siddley Trident
Lockheed 1049 Super Constellation & 1649 Starliner
Lockheed L-100 Hercules Medium range freighter
Lockheed L-1011 TriStar 1/50/100/150/200/250 Medium to long range widebody airliner
Lockheed L-1011 TriStar 500 Long range widebody airliner
Lockheed L-188 Electra Turboprop airliner and freighter
McDonnell Douglas DC-9-30 Short range airliners
Sud SE-210 Caravelle Short range airliner
Tupolev Tu-104A Medium to long range airliner
Tupolev TU-114 long range airliner
Tupolev Tu-334 Short to medium range airliner prototype
Vickers VC10 Medium to long range airliner
These are the Boeing and Airbus planes excluded:
Airbus A300-600 Medium range widebody airliner
Airbus A300B2/B4 Medium range widebody airliner
Airbus A310 Medium to long range widebody airliner
Airbus A318 100 seat regional airliner
Airbus A319 Medium range airliner
Airbus A320 Short to medium range airliner
Airbus A321 Short to medium range narrowbody airliner
Airbus A330-200 Long range widebody airliner
Airbus A330-300 Large capacity medium to long range airliner
Airbus A340-200/300 Long range widebody airliner
Airbus A340-500/600 Long range widebody airliners
Airbus A380 High capacity, long range, twindeck, widebody airliner
Boeing 707 Medium to long range airliner and freighter
Boeing 717 Short to medium range airliner
Boeing 720 Medium range narrowbody airliner
Boeing 727 Short to medium range narrowbody airliner
Boeing 737 Short to medium range narrowbody airliner
Boeing 747 Long range high capacity widebody airliner
Boeing 747SP Long range high capacity widebody airliner
Boeing 757 Medium range narrowbody airliner
Boeing 767 Medium to long range widebody airliner
Boeing 777 Long range high capacity widebody airliner
Boeing 787-8 Dreamliner Long range widebody airliner
Boeing C-97 Stratofreighter Freighter
The MD-80 series is still in fairly widespread use, and it wasn't made by Boeing or Airbus either. The MD-11 is getting harder to find in passenger service, although it's still used for cargo.
Bombardier make regional jets but their new C series is a 737/A320 class 80-120 seat aircraft
Yes , of course.
Tupolev, Antonov, Douglas(I thinks at least they made earlier) and Ilyushin have made many.
While Boeing and Airbus are the most common, Russia, China , India etc. do use (or may be used) other airlines.
Thank you for your interest in this question.
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