Приведенный ниже код даст вам массив с уникальным 'Id_plane', сохранив данные первого объекта.
let data = [
{
DateCreated: "2020-10-10",
Ends: 15.5,
Id_plane: 1,
Id_sale: 4,
Id_scheduler: 6,
Starts: 7,
__isset_bitfield: 31
},
{
DateCreated: "2020-10-11",
Ends: 17,
Id_plane: 1,
Id_sale: 4,
Id_scheduler: 6,
Starts: 7,
__isset_bitfield: 31
},
{
DateCreated: "2020-10-12",
Ends: 17,
Id_plane: 2,
Id_sale: 4,
Id_scheduler: 6,
Starts: 4.2,
__isset_bitfield: 40
},
{
DateCreated: "2020-10-11",
Ends: 17,
Id_plane: 2,
Id_sale: 4,
Id_scheduler: 6,
Starts: 7,
__isset_bitfield: 31
},
];
data.map((item, index) => {
let matchingItems = data.filter(el => el.Id_plane === item.Id_plane);
matchingItems.map(matchingItem => {
let key = data.indexOf(matchingItem)
if (key !== index) {
data.splice(key, 1);
}
});
});
console.log(data);