In Biggles in the Orient, it is stated that the Vickers Wellington carrying 666 Squadron refuelled at Hinaidi Airfield, Baghdad, on its way to India. Although Hinaidi Airfield certainly existed, and continues to exist today, it is extremely unlikely that Biggles' aircraft would have used it.
Located about 6 miles from Baghdad, Hinaidi was established after World War 1 by the British Army. In 1922 the Royal Air Force took it over and expanded it into the major RAF base in Iraq, with maintenance units, civil cantonments and a hospital. However, by the terms of the Anglo-Iraqi tray of 1930, the base was to be handed over to the Iraqi government within 5 years of the treaty coming into force. In 1936, the RAF units began moving to a new base, RAF Habbaniya, about 50 miles away. Hinaidi was handed over to the Iraqi government in 1938 and it became the main airbase of the Royal Iraqi Air Force.
During the Anglo-Iraqi war in May 1941, forces loyal to the pro-German Iraqi regime which had taken over in a coup-de-etat launched attacks from Hinaidi against British forces. The air base was bombed by RAF Wellingtons operating out of Habbaniya. The war ended by the end of May 1941 with the restoration of the previous pro-British government.
Given that by 1944 (the date of the events of Biggles in the Orient) a pro-British government was in place, British aircraft might have had access to Hinaidi if needed. However it is extremely unlikely that an RAF ferry flight like Biggles' would have used Hinaidi when the RAF had two large and well equipped bases of its own in Iraq: RAF Habbaniya and RAF Shaibah which was near Basrah.
The use of Habbaniya as a staging post is well documented. Indeed, the Empire Flying boats of Imperial Airways (same as the one which carried Biggles to Alexandria) actually transited at Habbaniya, which was built by a large lake, on their way to destinations in the Far East.
Hinaidi was renamed Rashid Airfield by the Iraqis in 1941. Also spelled Rasheed, this remains the name of the airbase to this day.