After the marriage to Wyndham was annulled she returned to her family and developed a career as an interior decorator, creating lavish interiors, state rooms and public spaces for her father's shipping line, the Peninsular and Oriental Steam Navigation Company. In 1923 she launched the, and went on to design much of the interiors for the four P&O "R" class ships of 1925: SS Rawalpindi,, and, plus the in 1927.
Flying
In 1923 she took up flying, gaining her pilot's licence at the De Havilland Flying School, probably the second woman since World War I after 'Mrs Atkey', bought a plane, and expressed a determination to be the first woman to fly the Atlantic. She was regarded as a contemporary role model amongst women, with dark looks, graceful manner, and a habitually well-dressed and bejewelled appearance. She was noted for driving her Rolls-Royce at great speed and was a familiar sight in her Avrobiplane in the skies over South Ayrshire and Wigtownshire. She even participated in an "outside loop", the most dangerous of all stunts in air, with Capt. E. C. D. Herne as her pilot. During this manoeuvre her safety-strap broke but she clung to bracing wires while her body swung outside the plane like a stone twirled on the end of a piece of string. She was one of the first women in Britain to gain her Royal Aero Club pilot's licence and was later elected to the advisory committee of pilots to the British EmpireAir League.
Transatlantic flight
To achieve her transatlantic ambition Mackay bought a Stinson Detroiter, having been impressed by the aircraft during Ruth Elder's failed 1927 transatlantic attempt. It was shipped from the US to Britain and delivered to the Brooklandsmotor racing track, which at the time was also used as an airfield. She named it Endeavour. It was a monoplane with gold tipped wings and a black fuselage, powered by a nine-cylinder, Wright Whirlwind J-6-9 engine, with a cruising speed of. In early March 1928 the Daily Express discovered that Captain Hinchliffe and Mackay were preparing for a transatlantic attempt by carrying out test flights at RAF Cranwell and were staying at the George Hotel in Leadenham near Grantham. The story was silenced by Mackay's threatened legal action as she intended to depart in secret while her father was in Egypt, having promised her family she would not make the attempt. At 8:35 am on 13March 1928 Endeavour took off from RAF Cranwell, Lincolnshire, with minimal fuss as Hinchliffe had told only two friends he was going and Elsie registered under the pseudonym of 'Gordon Sinclair'.' Approximately five hours later, at 1.30 pm the chief lighthouse keeper at Mizen Head on the south west coast of Cork, Ireland saw the monoplane over the village of Crookhaven, on the great circle course for Newfoundland. A French steamer later reported seeing them still on course, but nothing else is known. A crowd of 5,000 is reputed to have waited for them at Mitchel Field, Long Island. In December 1928, eight months later, a single piece of identifiable undercarriage washed ashore in north west Ireland.
Commemoration
Elsie Mackay is commemorated by a stained glass window in the chancel of Glenapp Church in the parish of Ballantrae, Ayrshire. Rhododendrons, now somewhat overgrown, spell out "Elsie" on the opposite side of the glen. A street is named after her in Gander, Newfoundland and Labrador. Her financial legacy was the Elsie Mackay Fund, a £500,000 trust bequeathed by her father that was left to the British nation on 12 December 1928, for 50 years and used to help pay off the national debt.
