In 1934, MacGill started work at
Fairchild Aircraft's operations in
Longueuil as an assistant aeronautical engineer. She contributed to various aviation projects including the
Fairchild Super 71 (the first aircraft designed and built in Canada featuring a metal fuselage), the
Fairchild 82 (a bush plane), and the
Fairchild Sekani (twin-engined transport aircraft). She presented a paper, "Simplified Performance Calculations for Aeroplanes", to the Royal Aeronautical Society in Ottawa, on March 22, 1938, to high praise. It was later published in
The Engineering Journal. She also participated in the Canadian Broadcasting Corporation's six-part series,
The Engineer in War Time; her segment was called "Aircraft Engineering in Wartime Canada". In 1942, she was elected to the position of chairman of the EIC, Lakehead Branch, after having also served as their vice-chairman. Later that year MacGill was hired as Chief Aeronautical Engineer at Canadian Car and Foundry (CanCar). There she designed and tested a new
training aircraft, the
Maple Leaf Trainer II. The Maple Leaf Trainer was designed and first built in CanCar's Fort William (now
Thunder Bay) factories, where MacGill had moved. Although the Maple Leaf II did not enter service with any Commonwealth forces, ten (two were completed, but eight had to be assembled in Mexico) were sold to
Mexico where its high-altitude performance was important, given the many airfields from which it had to operate. Her role in the company changed when the factory was selected to build the
Hawker Hurricane fighter aircraft for the
Royal Air Force (RAF). The factory had to be quickly expanded from about 500 workers to 4,500 by war's end, half of them women. McGill was responsible for tooling up production for more than 25,000 precision parts; the parts had to be interchangeable with Hurricanes manufactured in the U.K. Numerous popular stories were published about her in the media as well, reflecting the public's fascination with this woman engineer. After Hurricane production ended, CanCar looked for new work and secured a contract from the
United States Navy to build
Curtiss SB2C Helldivers. Again MacGill was responsible for all engineering and production work, and the plant ultimately produced 835 aircraft, significantly contributing to Allied air power. This production did not go nearly as smoothly, and a continual stream of minor changes from
Curtiss-Wright (in turn demanded by the U.S. Navy) meant that full-scale production took a long time to get started. MacGill moved to
Toronto, where she set up an aeronautical engineering consulting business with Bill Soulsby in 1943. In 1946, she became a Technical Adviser for
International Civil Aviation Organization (ICAO), where she helped to draft International Air Worthiness regulations for the design and production of commercial aircraft. In 1947 she became the chairman of the
United Nations Stress Analysis Committee, the first woman ever to chair a U.N. committee. In 1952, MacGill presented a paper to the Society of Women Engineers (SWE) conference, "The Initiative in Airliner Design", that was subsequently published in
The Engineering Journal. A year later SWE awarded her their annual Achievement Award. ==Advocacy==