The Avro 691 Lancastrian was a passenger and mail transport aircraft of the 1940s.

In 1943 Avro converted a Lancaster bomber for civil transport duties with Trans-Canada Airlines. This was a success, and further 6 Lancaster X were converted with a lengthened streamlined nose and tailcone, and long-range fuel tanks in the place on the Lancaster's bomb-bay. The conversions were carried out by Victory Aircraft of Toronto, Canada. The power-plants were Packard_built Merlin 38 engines, and these Lancastrians were used by TCA on its Montreal_Prestwick route.

In 1945 deliveries commenced of 30 British-built Lancastrians for BOAC. On a demonstration flight on April 23, 1945 G-AGLF flew from England to Auckland, New Zealand in 3days 14 hours - 13,500 miles (21,700 km) at an average 220 mph (354 km/h).

The Lancastrian had rather limited cubic capcity and was most suited for transport of mail and VIP passengers. BOAC used it on England to Australia flights from May 31, 1945. It also served with the RAF, one of their planes named Aries completing the first airborne circumnavigation of the globe, and with Argentina.

Lancastrians were used for tests of various turboprop and jet engines. One powered with Rolls_Royce Nene turbojets is credited with the first international passenger jet flight. from London to Paris on November 23 1946. The flight time was just 41 minutes.

On August 2, 1947 Lancastrian G-AGWH Stardust of British South American Airways crashed in the Argentinean Andes after sending an apparently cryptic radio message, in what became known as the "Stendec incident". The wreckage was found 50 years later but the radio message remains a puzzle.