To achieve her transatlantic ambition Mackay bought a Stinson Detroiter, having been impressed by the aircraft during Ruth Elder's failed 1927 transatlantic attempt (despite an oil leak causing the failure 300 miles (480 km) over the Atlantic).
It was shipped from the US to Britain and delivered to the Brooklands motor 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, 300 horsepower (220 kW) Wright Whirlwind J-6-9 (R-975) engine, with a cruising speed of 84 miles per hour (135 km/h).

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 13 March 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 (a wheel with a serial number on it) washed ashore in north west Ireland.
To achieve her transatlantic ambition Mackay bought a Stinson Detroiter, having been impressed by the aircraft during Ruth Elder's failed 1927 transatlantic attempt (despite an oil leak causing the failure 300 miles (480 km) over the Atlantic). It was shipped from the US to Britain and delivered to the Brooklands motor 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, 300 horsepower (220 kW) Wright Whirlwind J-6-9 (R-975) engine, with a cruising speed of 84 miles per hour (135 km/h).
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 13 March 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 (a wheel with a serial number on it) washed ashore in north west Ireland.
Elsie Mackay