In 1918, Lieuteant Macready was assigned to McCook Field, the Army Signal Corps' new experimental test field in Dayton, Ohio.
On 3 August 1921, Lieutenant Macready became the first person to test fly an experimental aerial application system for spraying pesticides from an aircraft, flying the world's first "crop duster".

In 1921, he set an altitude record of 34,509 feet for which he was awarded the first of three consecutive Mackay trophies.
 On 28 September 1921 he had climbed to
34,508 feet in an experimental Le Pere biplane designed and modified at McCook Field and souped up with an engine turbo-supercharger.

October 5, 1922 Macready and Lieutenant Oakley G. Kelly set a world endurance record of 35 hours, 18 minutes and 30 seconds.

On 2–3 May 1923 with Kelly, Macready made the first non-stop coast-to-coast flight, from Roosevelt Field, formerly Mitchell Field, 2.3 miles south-east of Mineola, Long Island, New York to Rockwell Field, North Island, San Diego, California, with a total flight time of 26 hours, 50 minutes and 48 seconds.
En route, he made the first in-flight aircraft engine repair in Air Service history, replacing a defective voltage regulator switch while the single engine, high wing Fokker T-2 Liberty mono-plane churned westward.
The flight also set a new distance record for a single cross-country flight, 2,625 miles.

At McCook, he also became the first pilot to bail out of a stricken aircraft at night.
On 13 June 1924, while he was making a night airways flight from McCook Field to Columbus, Ohio and back, his engine died just as he was approaching Dayton.
His first idea was to make an emergency landing, but the two flares he released failed to ignite.
Even though no one had ever made an emergency jump at night, he decided to trust to his parachute and came down safely, though his parachute tangled in a tree and he required help to get to the ground.
In 1918, Lieuteant Macready was assigned to McCook Field, the Army Signal Corps' new experimental test field in Dayton, Ohio. On 3 August 1921, Lieutenant Macready became the first person to test fly an experimental aerial application system for spraying pesticides from an aircraft, flying the world's first "crop duster".
In 1921, he set an altitude record of 34,509 feet for which he was awarded the first of three consecutive Mackay trophies.  On 28 September 1921 he had climbed to
34,508 feet in an experimental Le Pere biplane designed and modified at McCook Field and souped up with an engine turbo-supercharger.
October 5, 1922 Macready and Lieutenant Oakley G. Kelly set a world endurance record of 35 hours, 18 minutes and 30 seconds.
On 2–3 May 1923 with Kelly, Macready made the first non-stop coast-to-coast flight, from Roosevelt Field, formerly Mitchell Field, 2.3 miles south-east of Mineola, Long Island, New York to Rockwell Field, North Island, San Diego, California, with a total flight time of 26 hours, 50 minutes and 48 seconds. En route, he made the first in-flight aircraft engine repair in Air Service history, replacing a defective voltage regulator switch while the single engine, high wing Fokker T-2 Liberty mono-plane churned westward. The flight also set a new distance record for a single cross-country flight, 2,625 miles.
At McCook, he also became the first pilot to bail out of a stricken aircraft at night. On 13 June 1924, while he was making a night airways flight from McCook Field to Columbus, Ohio and back, his engine died just as he was approaching Dayton. His first idea was to make an emergency landing, but the two flares he released failed to ignite. Even though no one had ever made an emergency jump at night, he decided to trust to his parachute and came down safely, though his parachute tangled in a tree and he required help to get to the ground.
John A. Macready